A Review of Evolving Network Technology Ethernet & IP J.J. Ekstrom March 2008.
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Transcript of A Review of Evolving Network Technology Ethernet & IP J.J. Ekstrom March 2008.
A Review of Evolving Network Technology
Ethernet & IP
J.J. EkstromMarch 2008
Who is winning? Ethernet has won the LAN wars Ethernet is winning the MAN wars
– IProvo, Utopia… 10X bandwidth same price. Ethernet is contending for part of the WAN… PPOE (Point to Point
over Ethernet) IP has won all best-effort wars wars…
– Most ATM traffic is IP– A large portion of Sonet Traffic is IP– MPLS is taking over the core to optimize IP
IETF and Vendors making IP transport of choice for future– Voice over IP – IP Multicast Streaming
Why?
Simple transports Work faster and cheaper Put the smarts where it can work for more
transports Not as much advantage to smarter
transports
Historical View: Ethernet Characteristics
Ethernet shared media cable Cable access method (CSMA/CD) Unreliable Packet Delivery Assumes higher layers do most of the work Simple and Relatively fast on whatever
physical transport with any generation of hardware.
Ethernet Shared Media Cable 1
Physics determined the maximum length of the Ethernet cable– signal strength– cable characteristics
Ethernet Shared Media Cable 2
All stations (nodes) hook to, and share a single cable
Ethernet Shared Media Cable 3
Each station “listens” as it transmits
Ethernet Shared Media Cable 4
Each station must transmit a minimum of 64 bytes to “fill” the cable before it stops listening
64 bytes min.
Ethernet Shared Media Cable 5
If a 2nd node transmits before the 1st node finishes, the two transmissions collide and they must retransmit
64 bytes min. 64 bytes min.
Ethernet Cable Access Method (CSMA/CD)
CSMA/CD is a media-access method used by Ethernet and 802.3 networks
CSMA/CD stands for Carrier Sense, Multiple Access / Collision Detection
How CSMA/CD Works - 1
A station wishing to transmit first listens for traffic on the cable indicated by a carrier signal (CSMA/CD-Carrier Sense)
Network Cable Carrier Signal
How CSMA/CD Works - 2
If the carrier signal is detected, the station waits a period of time and tries again
Network Cable Carrier Signal
How CSMA/CD Works - 3
If NO carrier signal is detected, the station starts transmitting its packet (min. of 64 bytes) and simultaneously listening
Network CableM
IN. O
F 6
4 B
YTE
S
How CSMA/CD Works - 4
TWO stations can start transmitting at the same time (CSMA/CD - Multiple Access)
Network Cable
MIN
. O
F 6
4 B
YTE
S
MIN
. O
F 6
4 B
YTE
S
How CSMA/CD Works - 5
If this happens, both stations hear garbage (CSMA/CD - Collision Detection)
Network Cable
MIN
. O
F 6
4 B
YTES
MIN
. O
F 6
4 B
YTES@&*!
How CSMA/CD Works - 6
When collisons are detected, both stations :– cancel transmissions by sending a jam signal– wait a random amount of time before trying to
transmit again
Network Cable
JAM
SIG
NA
L
JAM
SIG
NA
L
PROBLEM #1
Physics doesn’t allow you to have LAN wires as long as you would like.
SOLUTION #1
Repeater extended wire length, broadcast domain, and collision domain
Repeater
PROBLEM #2
Too many collisions. LAN wouldn’t carry enough traffic.
SOLUTION #2
Bridging segments extends broadcast domain without collisions: Bigger LANs
BRIDGE
PROBLEM #3 Broadcast storms - result from multi-port
bridges “flooding” all ports when packet destination is unknown and a loop exists.
BRIDGE 1
BRIDGE 3 BRIDGE 2
64 bytes min.
Packet returningto original bridge
PROBLEM #3– when the original packet returns to a previous
bridge, new packets are generated and a “storm” is generated.
BRIDGE
BRIDGE BRIDGE
Cycle Repeats
SOLUTION #3
3.1 - 802.1D (spanning tree) installed on bridges.
3.2 - Routers
SOLUTION #3.1
802.1D (Spanning Tree) added to bridges. – Spanning Tree is an algorithm that runs on
bridges to eliminate loops dynamically.
802.1DBRIDGE 1
802.1DBRIDGE 3
802.1DBRIDGE 2
64 bytes min.
802.1D (SpanningTree) determines thatthis link is redundant
and shuts it down
SOLUTION #3.2 Routers - make every segment another
network or subnet by refusing to pass through any packet whose address it does not recognize.
BRIDGE 1
BRIDGE 2
64 bytes min.
RouterBRIDGE 3
SOLUTION #3.2 NOTE:
– in XNS a single broadcast domain is called a “network.”
– in TCP a single broadcast domain is called a “subnet.”
– network personnel often call a collision domain a “segment.”
PROBLEM #4 Topology and failure characteristics -
problems with bus-oriented LANs (i.e., when the wire breaks NONE of the stations can communicate).
SOLUTION #4
Twisted pair LANs.– When any one wire segment fails, the whole
LAN does NOT go down.
Concentrator ConcentratorBridge
Concentrator
PROBLEM #5
Not enough Bandwidth– only 10 MBPS available on each collision
domain
BRIDGE
BRIDGE
BRIDGEConcentrator
Concentrator
Concentrator
SOLUTION #5
Switches (multiport Bridges) - allows more segments (bandwidth) at a lower cost per port.
Concentrator
Concentrator
SWITCH
PROBLEM #6
Controlling User Connectivity– keep groups separate– easily share resources between groups– do adds, moves, and changes without rewiring
SOLUTION #6 VLANs of various forms create isolated
broadcast domains (networks) Connection between Virtual LAN networks
requires a router. People do security in their routers and
firewalls at network boundaries anyway
Problem #7
During roughly the same 20-25 year period Token-Ring LANs, FDDI, ATM, and several other LAN and WAN technologies have been undergoing similar evolutionary tracks as ethernet.
It was not clear that there would be a clear winner. How do you hook them together and protect your
technology investments? Users don’t care how their bits get pushed around,
only that things work.
Solution #7
Internetworking…The real reason IP has won the protocol wars.– Works well on P2P links
– Works well on LANs
– Makes very few demands of participant networks
– “Rough consensus and working code” Motto of the IETF The way to get useful things quickly in a world of confusion…
what works best wins.
Internetworking
Outline Best Effort Service ModelGlobal Addressing Scheme
IP Internet
Concatenation of Networks
Protocol Stack
R2
R1
H4
H5
H3H2H1
Network 2 (Ethernet)
Network 1 (Ethernet)
H6
Network 3 (FDDI)
Network 4(point-to-point)
H7 R3 H8
R1
ETH FDDI
IPIP
ETH
TCP R2
FDDI PPP
IP
R3
PPP ETH
IP
H1
IP
ETH
TCP
H8
Service Model Connectionless (datagram-based) Best-effort delivery (unreliable service)
– packets are lost– packets are delivered out of order– duplicate copies of a packet are delivered– packets can be delayed for a long time– (Sound like Ethernet?)
Datagram format Version HLen TOS Length
Ident Flags Offset
TTL Protocol Checksum
SourceAddr
DestinationAddr
Options (variable) Pad(variable)
0 4 8 16 19 31
Data
Fragmentation and Reassembly
Each network has some MTU Strategy
– fragment when necessary (MTU < Datagram)– try to avoid fragmentation at source host– re-fragmentation is possible – fragments are self-contained datagrams– use CS-PDU (not cells) for ATM– delay reassembly until destination host– do not recover from lost fragments
Example
H1 R1 R2 R3 H8
ETH IP (1400) FDDI IP (1400) PPP IP (512)
PPP IP (376)
PPP IP (512)
ETH IP (512)
ETH IP (376)
ETH IP (512)
Ident = x Offset = 0
Start of header
0
Rest of header
1400 data bytes
Ident = x Offset = 0
Start of header
1
Rest of header
512 data bytes
Ident = x Offset = 512
Start of header
1
Rest of header
512 data bytes
Ident = x Offset = 1024
Start of header
0
Rest of header
376 data bytes
Global Addresses Properties
– globally unique– hierarchical: network + host
Dot Notation– 10.3.2.4– 128.96.33.81– 192.12.69.77
Network Host
7 24
0A:
Network Host
14 16
1 0B:
Network Host
21 8
1 1 0C:
Datagram Forwarding Strategy
– every datagram contains destination’s address– if directly connected to destination network, then forward to host– if not directly connected to destination network, then forward to
some router– forwarding table maps network number into next hop– each host has a default router– each router maintains a forwarding table
Example (R2) Network Number Next Hop 1 R3 2 R1 3 interface 1 4 interface 0
Address Translation Map IP addresses into physical addresses
– destination host– next hop router
Techniques– encode physical address in host part of IP address– table-based
ARP– table of IP to physical address bindings– broadcast request if IP address not in table– target machine responds with its physical address– table entries are discarded if not refreshed
ARP Details
Request Format– HardwareType: type of physical network (e.g., Ethernet)– ProtocolType: type of higher layer protocol (e.g., IP)– HLEN & PLEN: length of physical and protocol addresses– Operation: request or response – Source/Target-Physical/Protocol addresses
Notes– table entries timeout in about 10 minutes– update table with source when you are the target – update table if already have an entry– do not refresh table entries upon reference
ARP Packet Format
TargetHardwareAddr (bytes 2 – 5)
TargetProtocolAddr (bytes 0 – 3)
SourceProtocolAddr (bytes 2 – 3)
Hardware type = 1 ProtocolType = 0x0800
SourceHardwareAddr (bytes 4 – 5)
TargetHardwareAddr (bytes 0 – 1)
SourceProtocolAddr (bytes 0 – 1)
HLen = 48 PLen = 32 Operation
SourceHardwareAddr (bytes 0 – 3)
0 8 16 31
Internet Control Message Protocol (ICMP)
Echo (ping) Redirect (from router to source host) Destination unreachable (protocol, port, or host) TTL exceeded (so datagrams don’t cycle forever) Checksum failed Reassembly failed Cannot fragment
Summary