CS419: Computer NetworksLecture 5, Part 1: Feb 14, 2005Internet RoutingCS419Routing and Forwarding RevisitedCS419Routing 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-domainCS419Internet 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-domainCS419Bridged 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-domainCS419DNS 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???CS419Distributed 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-domainCS419Internet IP Routing Architecture| The IP routing architecture is domain-based, with two tiersz Inter-domain and Intra-domain routing domainsCS419Autonomous Systems (AS)(i.e. routing domains)| But recall that the public Internet has a lot of structureCS419Transit ASs and Stub ASs (i.e. ISP and Site respectively)CS419Transit 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 ISsCS419Why 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 differentCS419Inter-domain and Intra-domain routing requirements| Inter-domain routing is mainly about policyz ISP A want to swap traffic with ISP Bz ISP A wants to load balance its traffic| Intra-domain routing is mainly about performancez Speed of convergence, traffic engineering, scalability| This suggests very different