414Lecture15

414Lecture15 - Lecture 15 Network Layer Hierarchical...

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Lecture 15 Network Layer Hierarchical Routing, RIP, OSPF, ISIS, EIGRP, BGP, IPv6 ECSE 414 – Fall 2010
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ECSE 414, Lecture 15 2 Announcements Homework Assignment #3 due today Midterms returned next lecture 2010 Michael Rabbat
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Link State vs. Distance Vector Link State Exchange info about entire network Dijkstra Need memory to store entire network topology Local errors do not propagate Link cost oscillations cause instability, loops Distance Vector Send DV messages to neighbors only Bellman-Ford updates Decentralized Scalable Sometimes slower convergence Good news travels fast Bad news travels slow Poisoned Reverse ECSE 414, Lecture 15 3 2010 Michael Rabbat
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ECSE 414, Lecture 15 4 Hierarchical Routing scale: with 200 million destinations: can’t store all dest’s in routing tables! routing table exchange would swamp links! administrative autonomy internet = network of networks each network admin may want to control routing in its own network Our routing study thus far - idealization all routers use identical routing protocol network “flat” … not true in practice 2010 Michael Rabbat
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ECSE 414, Lecture 15 5 Hierarchical Routing aggregate routers into regions, “autonomous systems” (AS) routers in same AS run same routing protocol “intra-AS” routing protocol routers in different ASes can run different intra-AS routing protocol Gateway router Direct link to router in another AS 2010 Michael Rabbat
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ECSE 414, Lecture 15 6 3b 1d 3a 1c 2a AS3 AS1 AS2 1a 2c 2b 1b Intra-AS Routing algorithm Inter-AS Routing algorithm Forwarding table 3c Interconnected ASes forwarding table configured by both intra- and inter-AS routing algorithm intra-AS sets entries for internal dests inter-AS & Intra-As sets entries for external dests 2010 Michael Rabbat
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ECSE 414, Lecture 15 7 3b 1d 3a 1c 2a AS3 AS1 AS2 1a 2c 2b 1b 3c Inter-AS tasks suppose router in AS1 receives datagram dest outside of AS1 router should forward packet to gateway router, but which one? AS1 must: 1. learn which dests reachable through AS2, which through AS3 2. propagate this reachability info to all routers in AS1 Job of inter-AS routing! 2010 Michael Rabbat
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ECSE 414, Lecture 15 8 Example: Setting forwarding table in router 1d suppose AS1 learns (via inter-AS protocol) that subnet x reachable via AS3 (gateway 1c) but not via AS2. inter-AS protocol propagates reachability info to all internal routers. router 1d determines from intra-AS routing info that its interface I is on the least cost path to 1c. installs forwarding table entry (x,I) 3b 1d 3a 1c 2a AS3 AS1 AS2 1a 2c 2b 1b 3c x 2010 Michael Rabbat
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ECSE 414, Lecture 15 9 Example: Choosing among multiple ASes now suppose AS1 learns from inter-AS protocol that subnet x is reachable from AS3 and from AS2. to configure forwarding table, router 1d must
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This note was uploaded on 05/09/2011 for the course ECSE 414 taught by Professor Rabbat during the Fall '10 term at McGill.

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414Lecture15 - Lecture 15 Network Layer Hierarchical...

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