UMD ENEE 426 - IP Routing (14 pages)

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IP Routing



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IP Routing

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Pages:
14
School:
University of Maryland, College Park
Course:
Enee 426 - Communication Networks

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IP Routing Networks as Graphs Networks are graphs Edges communication links Vertices computers switches routers etc For packet inbound at a particular vertex determine what output edge to use ENEE 426 Communication Networks Spring 2008 Lecture 17 Routers Processes IP header on inbound packets Uses destination IP address to determine through which interface the packet should be routed Host Host Application Virtual Connection Application TCP Router TCP IP IP IP MAC MAC MAC MAC PHY PHY PHY PHY ENEE 426 Communication Networks Spring 2008 Lecture 17 Approaches Discussed some approaches for packet switching Virtual Circuits Switching Tables Source Routing Not scalable on the Internet Imagine running STP across entire Internet Each network independent administrative domain local policy controls local configuration Need way to route between networks not between computers ENEE 426 Communication Networks Spring 2008 Lecture 17 Routing Tables Each host both computers and routers maintain a list of next hops in addition to a default route Residential Host Residential Router Network Interface Gateway 192 168 0 123 32 lo0 192 168 0 0 24 eth0 0 0 0 0 0 eth0 192 168 0 1 Network Interface Gateway 192 168 0 0 24 eth0 12 34 56 0 23 wan0 0 0 0 0 0 wan0 12 34 56 1 Core Internet routers have very large routing tables for every top level network ENEE 426 Communication Networks Spring 2008 Lecture 17 Building Routing Tables Statically configured Works well for end hosts configured via DHCP Bad for core routers with complex routing tables Need algorithms for automatically populating routing tables ENEE 426 Communication Networks Spring 2008 Lecture 17 Distance Vector Routing Based on Bellman Ford Algorithm Computes single source shortest path on a weighted digraph http links math rpi edu applets appindex graphtheory html Run Bellman Ford for all nodes Each node initializes a vector V of all routers Entries equal weight to neighbors and infinity to others initially During each iteration Send



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