lec-30 - What's Next. Network Layer Network layer service...

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1 Nov 2008  BITS C481 (Computer Networks) 1 What’s Next… Network Layer Network layer service models (Done!!!) Forwarding versus routing (Done!!!) How a router works (Done!!!) Internet protocol (Done!!!) Routing (path selection) Algorithms Dijkstra’s algorithm Distance Vector Hierarchical Routing Routing Protocols (Today!!!) RIP BGP OSPF Multicast Routing (Next Class…….)
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1 Nov 2008  BITS C481 (Computer Networks) 2 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 identical Network “flat” … not true in practice
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1 Nov 2008  BITS C481 (Computer Networks) 3 Hierarchical Routing Aggregate routers into regions, “autonomous systems” (AS) Routers in same AS run same routing protocol “intra-AS” routing protocol Routers in different AS can run different intra-AS routing protocol Gateway router Direct link to router in another AS
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1 Nov 2008  BITS C481 (Computer Networks) 4 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 is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries for internal destinations Inter-AS & Intra-As sets entries for external destinations
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1 Nov 2008  BITS C481 (Computer Networks) 5 3b 1d 3a 1c 2a AS3 AS1 AS2 1a 2c 2b 1b 3c Inter-AS tasks Suppose router in AS1 receives datagram for which destination is outside of AS1 Router should forward packet towards one of the gateway routers, but which one? AS1 needs: 1. To learn which destinations are reachable through AS2 and which through AS3 2. To propagate this reachability information to all routers in AS1 << Job of inter-AS routing!>>
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1 Nov 2008  BITS C481 (Computer Networks) 6 Example: Setting forwarding table in router 1d Suppose AS1 learns (via inter-AS protocol) that subnet x is reachable via AS3 (gateway 1c) but not via AS2. Inter-AS protocol propagates reachability information to all internal routers. Router 1d determines from intra-AS routing information that its interface
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This note was uploaded on 07/20/2009 for the course CONPUTER S BITS C481 taught by Professor Prof.virendersinghshekhawat during the Fall '08 term at Birla Institute of Technology & Science, Pilani - Hyderabad.

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lec-30 - What's Next. Network Layer Network layer service...

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