CISCO NETWORKING ACADEMY Chabot College ELEC 99.05 Ethernet Switches.

CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY

Chabot CollegeChabot College

ELEC 99.05ELEC 99.05Ethernet Switches


Ethernet Switch BasicsEthernet Switch Basics• Layer 2 device• Uses MAC addressing to control traffic flow• Supports multiple simultaneous

conversations• Reduces needless LAN traffic


Basics: Layer 2 DeviceBasics: Layer 2 Device• Switch understands layer 2 addresses

(MAC addresses):

00-C0-F0-56-BD-98


Basics: MAC Address UseBasics: MAC Address Use• Switch does not act like hub!• Switch forwards frames based on

MAC address tables.

I

H

G

FEDA B C

MAC AddressTable


Basics: MAC Address UseBasics: MAC Address Use• Switch “learns” MAC addresses of hosts

connected to switch ports as it receives frames from those ports:

I

H

G

FEDA B C

AC E

G H

MAC AddressTable


Basics: Multiple Data PathsBasics: Multiple Data Paths• Switch can create several simultaneous data

paths or “conversations”:

B C D E F G I

A


Switches Reduce Needless Switches Reduce Needless LAN TrafficLAN Traffic

• Each switch port defines a collision domain.

• Users on hub Aonly see trafficfrom/to theirworkgroup.

Hub Hub

Switch - 1 port per hub


Advanced FeaturesAdvanced Features• Switching matrix• Addressing• Multiple data rates• Full duplex• Port trunking• VLANs• Inter-switch communications• Modular Chassis


Switching Matrix (Fabric)Switching Matrix (Fabric)• Store & Forward

– stores entire incoming frame in memory buffer– performs error detection– drops bad frames– forwards good frames to destination port

based on MAC address– takes time - “high latency”


Switching Matrix (Fabric)Switching Matrix (Fabric)• Cut-through (cross-point)

– reads frame only as far as destination address field

– immediately forwards all frames to destination port based on MAC address

– no error checking; forwards bad frames(usually not a serious problem)

– fast - “low latency” (“wire speed”)


Addressing CapabilityAddressing Capability• 1 MAC address per port

– used with “port switching”

– microsegmentation

Switch - 1 port per PC


Addressing CapabilityAddressing Capability• 1 MAC address per port

– used with “port switching”– microsegmentation

• Multiple MAC addresses per port– used with “segment

switching”

Switch - 1 port per PC

Hub Hub

Switch - 1 port per hub


Multiple Data Transfer RatesMultiple Data Transfer Rates• Ports at 10mb/s and 100 mb/s• Requires “flow control”

B C D E F G I

Server

100

10 10 10 10 10 10 10

Otherwise, a fast server on a 100 mb portcould overflow the buffer of a 10 mb port.


Full Duplex PortsFull Duplex Ports• Ports can transmit & receive simultaneously.• Useful mainly for servers.• Possible only when there is one host per port

(no collisions).• Modern NICs “auto-sense” a full-duplex

switch port& turn on FD.


Port TrunkingPort Trunking• Ports can “trunked” (linked together) to form a

high bandwidth channel between switches:

300

CampusCore

Switch

BuildingSwitch


Tiered BandwidthTiered Bandwidth• Bandwidth can be placed where it is needed

most:

Workgroup Switch

D E F G I

100

10 10 10 10 10

Workgroup Switch

J K L M N

100

10 10 10 10 10

300

CampusCore

Switch

BuildingSwitch


VLANsVLANs• Switch ports can be separated into groups

called VLANs (virtual LANs)

VLAN1 VLAN2

D E F G I J

LAN2

D E F G I J

LAN1 sameas


VLANsVLANs• Each VLAN forms a broadcast domain.• Each VLAN is a separate Local Area Network

VLAN1 VLAN2

D E F G I J

LAN2

D E F G I J

LAN1 sameas


VLANsVLANs• VLAN can be cross-connected by routers.

(just like LANs)

VLAN1 VLAN2

D E F G I J

LAN2

D E F G I J

LAN1 sameas


Inter-Switch CommunicationInter-Switch Communication• Vendor-specific frame technologies allow

switches to communicate.• Cisco’s version is ISL (Inter Switch Link)• Allows VLANs to span several switches.• Hosts G, I, J, K are all part of VLAN 2:

D E F G I J K L M N

VLAN1 VLAN2 VLAN2 VLAN3

ISL


Modular ChassisModular Chassis• Large switches often use a modular chassis

that accepts various:– “switching engines”– interface modules– power supplies

• The Cisco Catalyst 5000 and 5505 are examples used on the Chabot campus


Catalyst 5000 ChassisCatalyst 5000 ChassisSD

POWER115/230 VAC9.8/4.9 A60/50Hz

POWER115/230 VAC9.8/4.9 A60/50Hz

1

1

1

1

1STATUS

SUPERVISOR ENGINE

FAN

PS2

PS1 RESET 100%SWITCH

LOAD1%

100Mbps

LINK

MDI X

100Mbps

LINK

MDI X

STATUS

ETHERNET SWITCHING MODULE

TXRX TX

RX TXRX TX

RX TXRX TX

RX TXRX TX

RX TXRX TX

RX TXRX TX

RX

1 2 3 4 5 6 7 8 9 10 11 12

ETHERNET SWITCHING

STATUS 1-4 5-8 9-1213-16

17-2021-24

ETHERNET SWITCHING

STATUS 1-4 5-8 9-1213-16

17-2021-24

STATUS

ETHERNET SWITCHING MODULE

TXRX TX

RX TXRX TX

RX TXRX TX

RX TXRX TX

RX TXRX TX

RX TXRX TX

RX

1 2 3 4 5 6 7 8 9 10 11 12

CISCO NETWORKING ACADEMY Chabot College ELEC 99.05 Ethernet Switches.

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