E6998-02: Internet Routing Lecture 5 Fundamentals of Routing Protocols John Ioannidis AT&T Labs – Research ji+ir@cs.columbia.edu Copyright © 2002 by John Ioannidis. All Rights Reserved.
Lecture 05 of E6998-02: Internet Routing Announcements Lectures 1-5 are available. Guest Lecturer on 9/19: Noel Chiappa. BE THERE! In a different room (check the bboard right before class). Lecture on 9/26 will be at 4:10pm in 1024. W4180 on 9/26 will be at 2:40pm in 1127. Homeworks submitted incorrectly. Don’t do it again. Homework 2 will be out later tonight. I assume that only people who submitted homeworks are in the class. September 17th, 2002 Lecture 05 of E6998-02: Internet Routing
Lecture 05 of E6998-02: Internet Routing Internet is a collection of connected nodes. End nodes (“end systems”): hosts. Connecting nodes (“intermediate systems”): routers. Internet is organized as a collection of networks. Customer networks. ISPs. Of varying sizes and purposes. Within a customer network or ISP: Cohesive routing policy. Performance and optimal internal routing is top priority. Between networks or ISPs: Different routing policies. Connectivity and abiding to policies is top priority. September 17th, 2002 Lecture 05 of E6998-02: Internet Routing
Lecture 05 of E6998-02: Internet Routing Routing Protocols Manual configuration (static routes). Too hard. Does not scale. Does not respond quickly to changing topologies. Source routing. Source decides path of packets (LSRR/SSRR options). Has been considered in the past (SDRP). Still question about how routes are computed. Dynamic routing. Distance-vector protocols. Link-state protocols. Other. September 17th, 2002 Lecture 05 of E6998-02: Internet Routing
Lecture 05 of E6998-02: Internet Routing Distance-Vector September 17th, 2002 Lecture 05 of E6998-02: Internet Routing
Lecture 05 of E6998-02: Internet Routing Distance-Vector Variations of Bellman-Ford algorithm. Each router starts by knowing: Prefixes of its attached networks (“zero” distance). Its next hop routers (how to find them?) Each router advertises only to its neighbors: All prefixes it knows about. Its distance from them. Each router learns: All prefixes its neighbors know about. Their distance from them. Each router figures out, for each destination prefix: The “distance” (how far away it is). The “vector” (the next hop router). September 17th, 2002 Lecture 05 of E6998-02: Internet Routing
Lecture 05 of E6998-02: Internet Routing Link-State Based on Dijkstra’s Shortest-Path-First algorithm. Each router starts by knowing: Prefixes of its attached networks. Links to its neighbors. Each router advertises to the entire network (flooding): Prefixes of its directly connected networks. Active links to its neighbors. Each router learns: A complete topology of the network (routers, links). Each router computes shortest path to each destination. In a stable situation, all routers have the same graph, and compute the same paths. September 17th, 2002 Lecture 05 of E6998-02: Internet Routing
Lecture 05 of E6998-02: Internet Routing DV A B C A:0 B:0 C:0 G G:0 F E D E:0 D:0 F:0 September 17th, 2002 Lecture 05 of E6998-02: Internet Routing
Lecture 05 of E6998-02: Internet Routing DV A B C A:0 B:1,B B:0 A:1,A E:1,E C:1,C C:0 B:1,B D:1,D G:1,G G G:0 C:1,C D:1,D F E D E:0 F:1,F B:1,B D:1,B D:0 E:1,E C:1,C G:1,G F:0 E:1,E September 17th, 2002 Lecture 05 of E6998-02: Internet Routing
Lecture 05 of E6998-02: Internet Routing DV A B C A:0 B:1,B C:2,B E:2,B B:0 A:1,A E:1,E C:1,C D:2,C G:2,C F:2,E C:0 B:1,B D:1,D G:1,G A:2,B E:2,B G G:0 C:1,C D:1,D F E D E:0 F:1,F B:1,B D:1,D D:0 E:1,E C:1,C G:1,G F:0 E:1,E September 17th, 2002 Lecture 05 of E6998-02: Internet Routing