Internet AS Hierarchy Intra-AS border(exterior gateway)routers C b B a Aa b Ac c a b Inter-AS interior(gateway)routers 4: Network Layer 4b-6
4: Network Layer 4b-6 Internet AS Hierarchy Intra-AS border (exterior gateway) routers Inter-AS interior (gateway) routers
Intra-AS Routing D Also known as Interior Gateway Protocols(IGP 口 Most common IGPs: o RIP: Routing information Protocol o OSPF: Open shortest path first o IGRP: Interior Gateway routing Protocol ( Cisco propr 4: Network Layer 4b-7
4: Network Layer 4b-7 Intra-AS Routing Also known as Interior Gateway Protocols (IGP) Most common IGPs: RIP: Routing Information Protocol OSPF: Open Shortest Path First IGRP: Interior Gateway Routing Protocol (Cisco propr.)
RIP(Routing Information Protocol) o Distance vector algorithm D Included in BSD-UNIX Distribution in 1982 o Distance metric: t of hops(max 15 hops) o Can you guess why? o Distance vectors: exchanged every 30 sec via Response Message(also called advertisement) D Each advertisement: route to up to 25 destination nets 4: Network layer 4b-8
4: Network Layer 4b-8 RIP ( Routing Information Protocol) Distance vector algorithm Included in BSD-UNIX Distribution in 1982 Distance metric: # of hops (max = 15 hops) Can you guess why? Distance vectors: exchanged every 30 sec via Response Message (also called advertisement) Each advertisement: route to up to 25 destination nets
RIP(Routing Information Protocol) A D B Destination Network Next Router Num. of hops to dest wyzx Routing table in d 4: Network layer 4b-9
4: Network Layer 4b-9 RIP (Routing Information Protocol) Destination Network Next Router Num. of hops to dest. w A 2 y B 2 z B 7 x -- 1 …. …. .... w x y z A C D B Routing table in D
RIP: Link Failure and Recovery If no advertisement heard after 180 sec neighbor/link declared dead o routes via neighbor invalidated o new advertisements sent to neighbors o neighbors in turn send out new advertisements(if tables changed) o link failure info quickly propagates to entire net o poison reverse used to prevent ping- pong loops (infinite distance 16 hops) 4: Network Layer 4b-10
4: Network Layer 4b-10 RIP: Link Failure and Recovery If no advertisement heard after 180 sec --> neighbor/link declared dead routes via neighbor invalidated new advertisements sent to neighbors neighbors in turn send out new advertisements (if tables changed) link failure info quickly propagates to entire net poison reverse used to prevent ping-pong loops (infinite distance = 16 hops)