lecture11 - Alan Mislove amislove at ccs.neu.edu...

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Unformatted text preview: Alan Mislove amislove at ccs.neu.edu Northeastern University 1 CS4700/CS5700 Fundamentals of Computer Networks Lecture 11: Intra-domain routing Slides used with permissions from Edward W. Knightly, T. S. Eugene Ng, Ion Stoica, Hui Zhang Alan Mislove amislove at ccs.neu.edu Northeastern University 2 What is Routing? • To ensure information is delivered to the correct destination at a reasonable level of performance • Forwarding – Given a forwarding table, move information from input ports to output ports of a router – Local mechanical operations • Routing – Acquires information in the forwarding tables – Requires knowledge of the network – Requires distributed coordination of routers Alan Mislove amislove at ccs.neu.edu Northeastern University 3 Viewing Routing as a Policy A E D C B F 2 2 1 3 1 1 2 5 3 5 Alan Mislove amislove at ccs.neu.edu Northeastern University 3 Viewing Routing as a Policy • Given multiple alternative paths, how to route information to destinations should be viewed as a policy decision A E D C B F 2 2 1 3 1 1 2 5 3 5 Alan Mislove amislove at ccs.neu.edu Northeastern University 3 Viewing Routing as a Policy • Given multiple alternative paths, how to route information to destinations should be viewed as a policy decision • What are some possible policies? – Shortest path (RIP, OSPF) – Most load-balanced – QoS routing (satisfies app requirements) – etc A E D C B F 2 2 1 3 1 1 2 5 3 5 Alan Mislove amislove at ccs.neu.edu Northeastern University 4 Internet Routing • Internet topology roughly organized as a two level hierarchy • First lower level – autonomous systems (AS’s) – AS: region of network under a single administrative domain • Each AS runs an intra-domain routing protocol – Distance Vector, e.g., Routing Information Protocol (RIP) – Link State, e.g., Open Shortest Path First (OSPF) – Possibly others • Second level – inter-connected AS’s • Between AS’s runs inter-domain routing protocols, e.g., Border Gateway Routing (BGP) – De facto standard today, BGP-4 Alan Mislove amislove at ccs.neu.edu Northeastern University 5 Example AS-1 AS-2 AS-3 Interior router BGP router Alan Mislove amislove at ccs.neu.edu Northeastern University 6 Why Need the Concept of AS or Domain? Alan Mislove amislove at ccs.neu.edu Northeastern University 6 Why Need the Concept of AS or Domain? • Routing algorithms are not efficient enough to deal with the size of the entire Internet Alan Mislove amislove at ccs.neu.edu Northeastern University 6 Why Need the Concept of AS or Domain? • Routing algorithms are not efficient enough to deal with the size of the entire Internet • Different organizations may want different internal routing policies Alan Mislove amislove at ccs.neu.edu Northeastern University 6 Why Need the Concept of AS or Domain?...
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lecture11 - Alan Mislove amislove at ccs.neu.edu...

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