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Unformatted text preview: 1 Csci 232 – Computer Networks Routing and Network Layer Part II 1 Routing: Network Layer Part II • Routing Algorithms: – Link state vs. Distance Vector • Routing in the Internet – Intra-AS vs. Inter-AS routing – Intra-AS: RIP and OSPF – Inter-AS: BGP and Policy Routing • MPLS Readings: Textbook: Chapter 4: Sections 4.2-4.3, 4.5-4.6 Csci 232 – Computer Networks Routing and Network Layer Part II 2 Routing & Forwarding: Logical View of a Router A E D C B F 2 2 1 3 1 1 2 5 3 5 Csci 232 – Computer Networks 3 Forwarding Process IP Forwarding Table Router 1. Remove a packet from an input queue 3. Match packet’s destination to a table entry 2. Check for sanity, decrement TTL field 4. Place packet on correct output queue If queues get full, just drop packets! If queues get full, just drop packets! IP Forwarding Process Csci 232 – Computer Networks 4 Destination Next Hop Interface Net A Net B Net C, Host 3 Router 1 Direct Router 2 Router 1 INT 7 INT 7 INT 3 INT 4 A destination is usually a network. May also be a host, or a “gateway of last resort” (default) The next hop is either a directly connected network or a router on a directly connected network A physical interface Net C IP Forwarding Table Csci 232 – Computer Networks 5 Statically Dynamically Routers exchange network reachability information using ROUTING PROTOCOLS . Routers use this to compute best routes Administrator manually configures forwarding table entries In practice : a mix of these. Static routing mostly at the “edge” + More control + Not restricted to destination-based forwarding - Doesn’t scale- Slow to adapt to network failures + Can rapidly adapt to changes in network topology + Can be made to scale well- Complex distributed algorithms- Consume CPU, Bandwidth, Memory- Debugging can be difficult- Current protocols are destination-based How Are Forwarding Tables Populated to Implement Routing? Csci 232 – Computer Networks Routing and Network Layer Part II 6 Dynamic Routing: Intra- vs. Inter-AS AS 1 AS 2 BGP EGP = Exterior Gateway Protocol IGP = Interior Gateway Protocol Metric based: OSPF, IS-IS, RIP, EIGRP (cisco) Policy based: BGP The Routing Domain of BGP is the entire Internet OSPF EIGRP 2 Csci 232 – Computer Networks Routing and Network Layer Part II 7 Internet AS Hierarchy border (exterior gateway) routers interior routers Csci 232 – Computer Networks Routing and Network Layer Part II 8 Intra-AS vs. Inter-AS Routing Host h2 a b b a a C A B d c A.a A.c C.b B.a c b Host h1 Intra-AS routing within AS A Inter-AS routing between A and B Intra-AS routing within AS B Csci 232 – Computer Networks Routing and Network Layer Part II 9 Intra-AS and Inter-AS Routing physical layer “Gateways”: •perform inter- AS routing amongst themselves •perform intra- AS routing with other routers in their AS inter-AS, intra-AS routing in gateway A.c network layer link layer a b b a a C A B d A.a A.c C.b B.a c b c Csci 232 – Computer Networks 10 Forwarding Table...
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This note was uploaded on 10/25/2009 for the course CS 232 taught by Professor Susan during the Fall '09 term at GWU.
- Fall '09