CS519: Computer NetworksLecture 4, Part 1: Feb 16, 2004Internet RoutingCS519Routing and Forwarding RevisitedCS519Routing has a huge design space| Type of addressz Hierarchical, flat, coordinate| Dynamic versus static| Centralized versus distributed| Hop-by-hop versus source route| Reactive versus proactive| Multi-domain versus single-domainCS519Internet IP routing| Type of addressz Hierarchical, flat, coordinate| Dynamic versus static| Centralized versus distributed| Hop-by-hop versus source route| Reactive versus proactive| Multi-domain versus single-domainCS519Bridged Ethernet Routing (versus IP Internet)| Type of addressz Hierarchical, flat, coordinate| Dynamic versus static| Centralized versus distributed| Hop-by-hop versus source route| Reactive versus proactive| Multi-domain versus single-domainCS519DNS Routing (versus IP Internet)| Type of addressz Hierarchical, flat, coordinate| Dynamic versus static| Centralized versus distributed| Hop-by-hop versus source route| Reactive versus proactive| Multi-domain versus single-domain???CS519Distributed Hash Table Routing (versus IP Internet)| Type of addressz Hierarchical, flat, coordinate| Dynamic versus static| Centralized versus distributed| Hop-by-hop versus source route| Reactive versus proactive| Multi-domain versus single-domainCS519Internet IP Routing Architecture| The IP routing architecture is domain-based, with two tiersz Inter-domain and Intra-domain routing domainsCS519Autonomous Systems (AS)(i.e. routing domains)| But recall that the public Internet has a lot of structureCS519Transit ASs and Stub ASs (i.e. ISP and Site respectively)CS519Transit ASs and Stub ASs| All transit ASs run BGP with each otherz Border Gateway Protocol| Stub ASs may or may not run BGPz Multi-homed Stubs typically will| All ASs internally run an intra-domain routing protocol| A large ISP may structure itself as multiple transit ISsCS519Why this 2-tier AS structure?| Why not just have all routers run BGP?| Answer: Autonomy| Different domains have different internal routing requirementsz Must be free to select a routing protocol to run internally| Inter-domain and Intra-domain routing requirements are quite differentCS519Inter-domain and Intra-domain routing requirements| Inter-domain routing is mainly about policyz ISP A has a contractual obligation to use ISP Bz ISP A wants to avoid ISP B| Intra-domain routing is mainly about performancez Speed of convergence, traffic engineering, scalability| This suggests very different
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