LANs to WANs Management guide

wlilakiatsakunText book

LANs to WANs The complete management guide

Topics

Local Area Networks (Revisited) LAN administration LAN restoration Planning Storage Network Management Managing Bridges Routers Gateways Managing the Wireless Infrastructure Managing Network Security WAN Restoration Planning

LAN (revisited)

Protocol ndashEthernetIEEE 8023 Define physical layer and MAC layer Media Access Control ndash CSMACD Contention-based meaning that station

compete with each other Addressing scheme

Devices HubSwitchRouter

Ethernetldquodominantrdquo wired LAN technology cheap $20 for 100Mbs first widely used LAN technology Simpler cheaper than token LANs and ATM Kept up with speed race 10 Mbps ndash 10 Gbps

Metcalfersquos Ethernetsketch

CSMA (Carrier Sense Multiple Access)

CSMA listen before transmitIf channel sensed idle transmit entire frame If channel sensed busy defer transmission

Human analogy donrsquot interrupt others

CSMA collisions

collisions can still occurpropagation delay means two nodes may not heareach otherrsquos transmissioncollisionentire packet transmission time wasted

spatial layout of nodes

noterole of distance amp propagation delay in determining collision probability

CSMACD (Collision Detection)

CSMACD carrier sensing deferral as in CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CSMACD collision detection

Addressing Scheme 32-bit IP address

network-layer address used to get datagram to destination IP subnet

MAC (or LAN or physical or Ethernet) address used to get datagram from one interface to

another physically-connected interface (same network)

48 bit MAC address (for most LANs) burned in the adapter ROM

LAN Addresses

Each adapter on LAN has unique LAN address

Broadcast address =FF-FF-FF-FF-FF-FF

= adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN(wired orwireless)

LAN Address (more)

MAC address allocation administered by IEEE MAC address is divided as following

First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices

manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E

MAC flat address portability can move LAN card from one LAN to another

IP hierarchical address NOT portable Sometimes it is called Physical address

Question how to determineMAC address of a hostknowing hostrsquos IP address

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

ARP protocol Same LAN (network)

A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table

A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query

B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)

A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes

away) unless refreshed ARP is ldquoplug-and-playrdquo

nodes create their ARP tables without intervention from net administrator

Routing to another LAN

walkthrough send datagram from A to B via R assume A knowrsquos B IP address

A

RB

A creates datagram with source A destination B

A uses ARP to get Rrsquos MAC address for 111111111110

A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram

Arsquos adapter sends frame Rrsquos adapter receives frame

R removes IP datagram from Ethernet frame sees its destined to B

R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram

sends to B

A

RB

LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more

later)

hub orswitch

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Topics

Local Area Networks (Revisited) LAN administration LAN restoration Planning Storage Network Management Managing Bridges Routers Gateways Managing the Wireless Infrastructure Managing Network Security WAN Restoration Planning

LAN (revisited)

Protocol ndashEthernetIEEE 8023 Define physical layer and MAC layer Media Access Control ndash CSMACD Contention-based meaning that station

compete with each other Addressing scheme

Devices HubSwitchRouter

Ethernetldquodominantrdquo wired LAN technology cheap $20 for 100Mbs first widely used LAN technology Simpler cheaper than token LANs and ATM Kept up with speed race 10 Mbps ndash 10 Gbps

Metcalfersquos Ethernetsketch

CSMA (Carrier Sense Multiple Access)

CSMA listen before transmitIf channel sensed idle transmit entire frame If channel sensed busy defer transmission

Human analogy donrsquot interrupt others

CSMA collisions

collisions can still occurpropagation delay means two nodes may not heareach otherrsquos transmissioncollisionentire packet transmission time wasted

spatial layout of nodes

noterole of distance amp propagation delay in determining collision probability

CSMACD (Collision Detection)

CSMACD carrier sensing deferral as in CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CSMACD collision detection

Addressing Scheme 32-bit IP address

network-layer address used to get datagram to destination IP subnet

MAC (or LAN or physical or Ethernet) address used to get datagram from one interface to

another physically-connected interface (same network)

48 bit MAC address (for most LANs) burned in the adapter ROM

LAN Addresses

Each adapter on LAN has unique LAN address

Broadcast address =FF-FF-FF-FF-FF-FF

= adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN(wired orwireless)

LAN Address (more)

MAC address allocation administered by IEEE MAC address is divided as following

First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices

manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E

MAC flat address portability can move LAN card from one LAN to another

IP hierarchical address NOT portable Sometimes it is called Physical address

Question how to determineMAC address of a hostknowing hostrsquos IP address

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

ARP protocol Same LAN (network)

A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table

A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query

B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)

A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes

away) unless refreshed ARP is ldquoplug-and-playrdquo

nodes create their ARP tables without intervention from net administrator

Routing to another LAN

walkthrough send datagram from A to B via R assume A knowrsquos B IP address

A

RB

A creates datagram with source A destination B

A uses ARP to get Rrsquos MAC address for 111111111110

A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram

Arsquos adapter sends frame Rrsquos adapter receives frame

R removes IP datagram from Ethernet frame sees its destined to B

R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram

sends to B

A

RB

LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more

later)

hub orswitch

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

LAN (revisited)

Protocol ndashEthernetIEEE 8023 Define physical layer and MAC layer Media Access Control ndash CSMACD Contention-based meaning that station

compete with each other Addressing scheme

Devices HubSwitchRouter

Ethernetldquodominantrdquo wired LAN technology cheap $20 for 100Mbs first widely used LAN technology Simpler cheaper than token LANs and ATM Kept up with speed race 10 Mbps ndash 10 Gbps

Metcalfersquos Ethernetsketch

CSMA (Carrier Sense Multiple Access)

CSMA listen before transmitIf channel sensed idle transmit entire frame If channel sensed busy defer transmission

Human analogy donrsquot interrupt others

CSMA collisions

collisions can still occurpropagation delay means two nodes may not heareach otherrsquos transmissioncollisionentire packet transmission time wasted

spatial layout of nodes

noterole of distance amp propagation delay in determining collision probability

CSMACD (Collision Detection)

CSMACD carrier sensing deferral as in CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CSMACD collision detection

Addressing Scheme 32-bit IP address

network-layer address used to get datagram to destination IP subnet

MAC (or LAN or physical or Ethernet) address used to get datagram from one interface to

another physically-connected interface (same network)

48 bit MAC address (for most LANs) burned in the adapter ROM

LAN Addresses

Each adapter on LAN has unique LAN address

Broadcast address =FF-FF-FF-FF-FF-FF

= adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN(wired orwireless)

LAN Address (more)

MAC address allocation administered by IEEE MAC address is divided as following

First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices

manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E

MAC flat address portability can move LAN card from one LAN to another

IP hierarchical address NOT portable Sometimes it is called Physical address

Question how to determineMAC address of a hostknowing hostrsquos IP address

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

ARP protocol Same LAN (network)

A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table

A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query

B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)

A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes

away) unless refreshed ARP is ldquoplug-and-playrdquo

nodes create their ARP tables without intervention from net administrator

Routing to another LAN

walkthrough send datagram from A to B via R assume A knowrsquos B IP address

A

RB

A creates datagram with source A destination B

A uses ARP to get Rrsquos MAC address for 111111111110

A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram

Arsquos adapter sends frame Rrsquos adapter receives frame

R removes IP datagram from Ethernet frame sees its destined to B

R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram

sends to B

A

RB

LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more

later)

hub orswitch

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Ethernetldquodominantrdquo wired LAN technology cheap $20 for 100Mbs first widely used LAN technology Simpler cheaper than token LANs and ATM Kept up with speed race 10 Mbps ndash 10 Gbps

Metcalfersquos Ethernetsketch

CSMA (Carrier Sense Multiple Access)

CSMA listen before transmitIf channel sensed idle transmit entire frame If channel sensed busy defer transmission

Human analogy donrsquot interrupt others

CSMA collisions

collisions can still occurpropagation delay means two nodes may not heareach otherrsquos transmissioncollisionentire packet transmission time wasted

spatial layout of nodes

noterole of distance amp propagation delay in determining collision probability

CSMACD (Collision Detection)

CSMACD carrier sensing deferral as in CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CSMACD collision detection

Addressing Scheme 32-bit IP address

network-layer address used to get datagram to destination IP subnet

MAC (or LAN or physical or Ethernet) address used to get datagram from one interface to

another physically-connected interface (same network)

48 bit MAC address (for most LANs) burned in the adapter ROM

LAN Addresses

Each adapter on LAN has unique LAN address

Broadcast address =FF-FF-FF-FF-FF-FF

= adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN(wired orwireless)

LAN Address (more)

MAC address allocation administered by IEEE MAC address is divided as following

First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices

manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E

MAC flat address portability can move LAN card from one LAN to another

IP hierarchical address NOT portable Sometimes it is called Physical address

Question how to determineMAC address of a hostknowing hostrsquos IP address

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

ARP protocol Same LAN (network)

A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table

A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query

B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)

A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes

away) unless refreshed ARP is ldquoplug-and-playrdquo

nodes create their ARP tables without intervention from net administrator

Routing to another LAN

walkthrough send datagram from A to B via R assume A knowrsquos B IP address

A

RB

A creates datagram with source A destination B

A uses ARP to get Rrsquos MAC address for 111111111110

A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram

Arsquos adapter sends frame Rrsquos adapter receives frame

R removes IP datagram from Ethernet frame sees its destined to B

R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram

sends to B

A

RB

LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more

later)

hub orswitch

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

CSMA (Carrier Sense Multiple Access)

CSMA listen before transmitIf channel sensed idle transmit entire frame If channel sensed busy defer transmission

Human analogy donrsquot interrupt others

CSMA collisions

collisions can still occurpropagation delay means two nodes may not heareach otherrsquos transmissioncollisionentire packet transmission time wasted

spatial layout of nodes

noterole of distance amp propagation delay in determining collision probability

CSMACD (Collision Detection)

CSMACD carrier sensing deferral as in CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CSMACD collision detection

Addressing Scheme 32-bit IP address

network-layer address used to get datagram to destination IP subnet

MAC (or LAN or physical or Ethernet) address used to get datagram from one interface to

another physically-connected interface (same network)

48 bit MAC address (for most LANs) burned in the adapter ROM

LAN Addresses

Each adapter on LAN has unique LAN address

Broadcast address =FF-FF-FF-FF-FF-FF

= adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN(wired orwireless)

LAN Address (more)

MAC address allocation administered by IEEE MAC address is divided as following

First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices

manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E

MAC flat address portability can move LAN card from one LAN to another

IP hierarchical address NOT portable Sometimes it is called Physical address

Question how to determineMAC address of a hostknowing hostrsquos IP address

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

ARP protocol Same LAN (network)

A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table

A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query

B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)

A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes

away) unless refreshed ARP is ldquoplug-and-playrdquo

nodes create their ARP tables without intervention from net administrator

Routing to another LAN

walkthrough send datagram from A to B via R assume A knowrsquos B IP address

A

RB

A creates datagram with source A destination B

A uses ARP to get Rrsquos MAC address for 111111111110

A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram

Arsquos adapter sends frame Rrsquos adapter receives frame

R removes IP datagram from Ethernet frame sees its destined to B

R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram

sends to B

A

RB

LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more

later)

hub orswitch

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

CSMA collisions

collisions can still occurpropagation delay means two nodes may not heareach otherrsquos transmissioncollisionentire packet transmission time wasted

spatial layout of nodes

noterole of distance amp propagation delay in determining collision probability

CSMACD (Collision Detection)

CSMACD carrier sensing deferral as in CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CSMACD collision detection

Addressing Scheme 32-bit IP address

network-layer address used to get datagram to destination IP subnet

MAC (or LAN or physical or Ethernet) address used to get datagram from one interface to

another physically-connected interface (same network)

48 bit MAC address (for most LANs) burned in the adapter ROM

LAN Addresses

Each adapter on LAN has unique LAN address

Broadcast address =FF-FF-FF-FF-FF-FF

= adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN(wired orwireless)

LAN Address (more)

MAC address allocation administered by IEEE MAC address is divided as following

First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices

manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E

MAC flat address portability can move LAN card from one LAN to another

IP hierarchical address NOT portable Sometimes it is called Physical address

Question how to determineMAC address of a hostknowing hostrsquos IP address

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

ARP protocol Same LAN (network)

A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table

A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query

B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)

A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes

away) unless refreshed ARP is ldquoplug-and-playrdquo

nodes create their ARP tables without intervention from net administrator

Routing to another LAN

walkthrough send datagram from A to B via R assume A knowrsquos B IP address

A

RB

A creates datagram with source A destination B

A uses ARP to get Rrsquos MAC address for 111111111110

A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram

Arsquos adapter sends frame Rrsquos adapter receives frame

R removes IP datagram from Ethernet frame sees its destined to B

R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram

sends to B

A

RB

LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more

later)

hub orswitch

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

CSMACD (Collision Detection)

CSMACD carrier sensing deferral as in CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CSMACD collision detection

Addressing Scheme 32-bit IP address

network-layer address used to get datagram to destination IP subnet

MAC (or LAN or physical or Ethernet) address used to get datagram from one interface to

another physically-connected interface (same network)

48 bit MAC address (for most LANs) burned in the adapter ROM

LAN Addresses

Each adapter on LAN has unique LAN address

Broadcast address =FF-FF-FF-FF-FF-FF

= adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN(wired orwireless)

LAN Address (more)

MAC address allocation administered by IEEE MAC address is divided as following

First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices

manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E

MAC flat address portability can move LAN card from one LAN to another

IP hierarchical address NOT portable Sometimes it is called Physical address

Question how to determineMAC address of a hostknowing hostrsquos IP address

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

ARP protocol Same LAN (network)

A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table

A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query

B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)

A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes

away) unless refreshed ARP is ldquoplug-and-playrdquo

nodes create their ARP tables without intervention from net administrator

Routing to another LAN

walkthrough send datagram from A to B via R assume A knowrsquos B IP address

A

RB

A creates datagram with source A destination B

A uses ARP to get Rrsquos MAC address for 111111111110

A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram

Arsquos adapter sends frame Rrsquos adapter receives frame

R removes IP datagram from Ethernet frame sees its destined to B

R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram

sends to B

A

RB

LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more

later)

hub orswitch

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

CSMACD collision detection

Addressing Scheme 32-bit IP address

network-layer address used to get datagram to destination IP subnet

MAC (or LAN or physical or Ethernet) address used to get datagram from one interface to

another physically-connected interface (same network)

48 bit MAC address (for most LANs) burned in the adapter ROM

LAN Addresses

Each adapter on LAN has unique LAN address

Broadcast address =FF-FF-FF-FF-FF-FF

= adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN(wired orwireless)

LAN Address (more)

MAC address allocation administered by IEEE MAC address is divided as following

First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices

manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E

MAC flat address portability can move LAN card from one LAN to another

IP hierarchical address NOT portable Sometimes it is called Physical address

Question how to determineMAC address of a hostknowing hostrsquos IP address

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

ARP protocol Same LAN (network)

A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table

A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query

B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)

A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes

away) unless refreshed ARP is ldquoplug-and-playrdquo

nodes create their ARP tables without intervention from net administrator

Routing to another LAN

walkthrough send datagram from A to B via R assume A knowrsquos B IP address

A

RB

A creates datagram with source A destination B

A uses ARP to get Rrsquos MAC address for 111111111110

A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram

Arsquos adapter sends frame Rrsquos adapter receives frame

R removes IP datagram from Ethernet frame sees its destined to B

R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram

sends to B

A

RB

LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more

later)

hub orswitch

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Addressing Scheme 32-bit IP address

network-layer address used to get datagram to destination IP subnet

MAC (or LAN or physical or Ethernet) address used to get datagram from one interface to

another physically-connected interface (same network)

48 bit MAC address (for most LANs) burned in the adapter ROM

LAN Addresses

Each adapter on LAN has unique LAN address

Broadcast address =FF-FF-FF-FF-FF-FF

= adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN(wired orwireless)

LAN Address (more)

MAC address allocation administered by IEEE MAC address is divided as following

First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices

manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E

MAC flat address portability can move LAN card from one LAN to another

IP hierarchical address NOT portable Sometimes it is called Physical address

Question how to determineMAC address of a hostknowing hostrsquos IP address

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

ARP protocol Same LAN (network)

A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table

A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query

B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)

A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes

away) unless refreshed ARP is ldquoplug-and-playrdquo

nodes create their ARP tables without intervention from net administrator

Routing to another LAN

walkthrough send datagram from A to B via R assume A knowrsquos B IP address

A

RB

A creates datagram with source A destination B

A uses ARP to get Rrsquos MAC address for 111111111110

A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram

Arsquos adapter sends frame Rrsquos adapter receives frame

R removes IP datagram from Ethernet frame sees its destined to B

R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram

sends to B

A

RB

LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more

later)

hub orswitch

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

LAN Addresses

Each adapter on LAN has unique LAN address

Broadcast address =FF-FF-FF-FF-FF-FF

= adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN(wired orwireless)

LAN Address (more)

MAC address allocation administered by IEEE MAC address is divided as following

First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices

manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E

MAC flat address portability can move LAN card from one LAN to another

IP hierarchical address NOT portable Sometimes it is called Physical address

Question how to determineMAC address of a hostknowing hostrsquos IP address

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

ARP protocol Same LAN (network)

A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table

A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query

B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)

A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes

away) unless refreshed ARP is ldquoplug-and-playrdquo

nodes create their ARP tables without intervention from net administrator

Routing to another LAN

walkthrough send datagram from A to B via R assume A knowrsquos B IP address

A

RB

A creates datagram with source A destination B

A uses ARP to get Rrsquos MAC address for 111111111110

A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram

Arsquos adapter sends frame Rrsquos adapter receives frame

R removes IP datagram from Ethernet frame sees its destined to B

R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram

sends to B

A

RB

LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more

later)

hub orswitch

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

LAN Address (more)

MAC address allocation administered by IEEE MAC address is divided as following

First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices

manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E

MAC flat address portability can move LAN card from one LAN to another

IP hierarchical address NOT portable Sometimes it is called Physical address

Question how to determineMAC address of a hostknowing hostrsquos IP address

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

ARP protocol Same LAN (network)

A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table

A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query

B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)

A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes

away) unless refreshed ARP is ldquoplug-and-playrdquo

nodes create their ARP tables without intervention from net administrator

Routing to another LAN

walkthrough send datagram from A to B via R assume A knowrsquos B IP address

A

RB

A creates datagram with source A destination B

A uses ARP to get Rrsquos MAC address for 111111111110

A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram

Arsquos adapter sends frame Rrsquos adapter receives frame

R removes IP datagram from Ethernet frame sees its destined to B

R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram

sends to B

A

RB

LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more

later)

hub orswitch

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

MAC flat address portability can move LAN card from one LAN to another

IP hierarchical address NOT portable Sometimes it is called Physical address

Question how to determineMAC address of a hostknowing hostrsquos IP address

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

ARP protocol Same LAN (network)

A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table

A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query

B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)

A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes

away) unless refreshed ARP is ldquoplug-and-playrdquo

nodes create their ARP tables without intervention from net administrator

Routing to another LAN

walkthrough send datagram from A to B via R assume A knowrsquos B IP address

A

RB

A creates datagram with source A destination B

A uses ARP to get Rrsquos MAC address for 111111111110

A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram

Arsquos adapter sends frame Rrsquos adapter receives frame

R removes IP datagram from Ethernet frame sees its destined to B

R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram

sends to B

A

RB

LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more

later)

hub orswitch

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

ARP protocol Same LAN (network)

A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table

A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query

B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)

A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes

away) unless refreshed ARP is ldquoplug-and-playrdquo

nodes create their ARP tables without intervention from net administrator

Routing to another LAN

walkthrough send datagram from A to B via R assume A knowrsquos B IP address

A

RB

A creates datagram with source A destination B

A uses ARP to get Rrsquos MAC address for 111111111110

A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram

Arsquos adapter sends frame Rrsquos adapter receives frame

R removes IP datagram from Ethernet frame sees its destined to B

R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram

sends to B

A

RB

LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more

later)

hub orswitch

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

ARP protocol Same LAN (network)

A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table

A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query

B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)

A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes

away) unless refreshed ARP is ldquoplug-and-playrdquo

nodes create their ARP tables without intervention from net administrator

Routing to another LAN

walkthrough send datagram from A to B via R assume A knowrsquos B IP address

A

RB

A creates datagram with source A destination B

A uses ARP to get Rrsquos MAC address for 111111111110

A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram

Arsquos adapter sends frame Rrsquos adapter receives frame

R removes IP datagram from Ethernet frame sees its destined to B

R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram

sends to B

A

RB

LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more

later)

hub orswitch

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes

away) unless refreshed ARP is ldquoplug-and-playrdquo

nodes create their ARP tables without intervention from net administrator

Routing to another LAN

walkthrough send datagram from A to B via R assume A knowrsquos B IP address

A

RB

A creates datagram with source A destination B

A uses ARP to get Rrsquos MAC address for 111111111110

A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram

Arsquos adapter sends frame Rrsquos adapter receives frame

R removes IP datagram from Ethernet frame sees its destined to B

R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram

sends to B

A

RB

LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more

later)

hub orswitch

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Routing to another LAN

walkthrough send datagram from A to B via R assume A knowrsquos B IP address

A

RB

A creates datagram with source A destination B

A uses ARP to get Rrsquos MAC address for 111111111110

A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram

Arsquos adapter sends frame Rrsquos adapter receives frame

R removes IP datagram from Ethernet frame sees its destined to B

R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram

sends to B

A

RB

LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more

later)

hub orswitch

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

A creates datagram with source A destination B

A uses ARP to get Rrsquos MAC address for 111111111110

A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram

Arsquos adapter sends frame Rrsquos adapter receives frame

R removes IP datagram from Ethernet frame sees its destined to B

R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram

sends to B

A

RB

LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more

later)

hub orswitch

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

R removes IP datagram from Ethernet frame sees its destined to B

R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram

sends to B

A

RB

LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more

later)

hub orswitch

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more

later)

hub orswitch

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock rates

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Ethernet Frame Structure (more)

Addresses 6 bytes if adapter receives frame with matching

destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol

otherwise adapter discards frame

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)

CRC checked at receiver if error is detected the frame is simply dropped

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Unreliable connectionless service

Connectionless No handshaking between sending and receiving adapter

Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can

have gaps gaps will be filled if app is using TCP otherwise app will see the gaps

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Ethernet uses CSMACD No slots adapter doesnrsquot transmit if

it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and

cheap

transprop tt 51

1efficiency

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

10BaseT and 100BaseT 10100 Mbps rate latter

called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub

ldquostar topologyrdquo 100 m max distance between nodes and hub

twisted pair

hub

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

HubsHubs are essentially physical-layer

repeaters bits coming from one link go out all

other links at the same rate no frame buffering no CSMACD at hub adapters detect

collisions provides net management functionality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Interconnecting with hubs

hub

hubhub

hub

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Backbone hub interconnects LAN segments

Extends max distance between nodes But individual segment collision domains

become one large collision domain If a link capacity is 10Mbps the overall

capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively

forwards frame based on MAC dest address when frame is to be forwarded on segment

uses CSMACD to access segment transparent

hosts are unaware of presence of switches plug-and-play self-learning

switches do not need to be configured

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Forwarding

bull How do determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be

60 min) switch learns which hosts can be reached

through which interfaces when frame received switch ldquolearnsrdquo

location of sender incoming LAN segment records senderlocation pair in switch table

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

FilteringForwarding

When switch receives a frameindex switch table using MAC dest addressif entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated else flood

forward on all except the interface on which the frame arrived

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Switch exampleSuppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3 frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Switch exampleSuppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1 frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Switch traffic isolation switch installation breaks subnet into

LAN segments

hub hub hub

switch

collision domain collision domain

collision domain

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

switch filters packets same-LAN-segment frames not

usually forwarded onto other LAN segments

segments become separate collision domains

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Switches dedicated access

Switch with many interfaces

Hosts have direct connection to switch

No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Switches vs Routers

both store-and-forward devices routers network layer devices (examine

network layer headers) switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Summary comparison hubs routers switches

traffi c isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Redundant topology

Networks with redundant paths and devices allow for more network uptime

Redundant topologies eliminate single points of failure

If a path or device fails the redundant path or device can take over the tasks of the failed path or device

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi

tch B Switches learn the MAC addresses of devices on

their ports so that data can be properly forward ed to the destination

Switches flood frames for unknown destinations until they learn the MAC addresses of the device

s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa

dcast storms multiple frame copies and MAC a ddress table instability problems

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Broadcast strom

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Spanning Tree Protocol

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Finally - there is one spanning tree per network On e very switched network

One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports

Root ports and designated ports are used for fo rwarding (F) data traffic

- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por

ts

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

VLAN (Virtual LAN) overview

VLANs allow almost complete independ ence of the physical and logical topologi

es Administrators can use VLANs to define

groupings of workstations even if they are separated by switches and on differ ent LAN segments

O ne VLAN means one collision domain a nd one broadcast domain

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

VLAN A VLAN is a logical group of network stati

ons services and devices that is not rest ricted to a physical LAN segment

VLANs facilitate easy administration of lo gical groups of stations and servers that c

an communicate as if they were on the sa me physical LAN segment

They also facilitate easier administration of moves adds and changes in members of these groups

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

VLAN services VLANs are created to provide segmentation servi

ces traditionally provided by physical routers in L AN configurations

VLANs address scalability security and network management

Routers in VLAN topologies provide broadcast filt ering security and traffic flow management

Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast

domain Traffic should only be routed between VLANs

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Static VLAN

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Dynamic VLAN

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

Port-centric VLAN

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

VLAN Transmission

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

VLANrsquos benefit

VLANs allow network administrators to or ganize LANs logically instead of physically

This allows network administrators to perf orm several tasks

Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality

VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas

ed on several factors Traffic patterns Types of applications Network management needs Group commonality