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Introduction to Internet Routing

Introduction to Internet Routing. Lixin Gao ECE Dept. UMASS, Amherst. Routing Protocols. Goal: Determine path or route Packet switching networks: determine routing table Routing Table: Used for forwarding each packet Scalable, adaptive, stable. Internet Protocol Stack. Application

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Introduction to Internet Routing

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  1. Introduction to Internet Routing Lixin Gao ECE Dept. UMASS, Amherst ECE697F: Special Topics-Internet Routing

  2. Routing Protocols • Goal: • Determine path or route • Packet switching networks: determine routing table • Routing Table: • Used for forwarding each packet • Scalable, adaptive, stable ECE697F: Special Topics-Internet Routing

  3. Internet Protocol Stack • Application • Transport • Network • Link • Physical ECE697F: Special Topics-Internet Routing

  4. Route Construction • Static • Listed Manually: change route slowly • not robust: reachability is independent of network condition • stable • Dynamic • Learn route via routing protocols • React to topology, traffic or configuration changes directly • Might not converge or oscillate • Might have loop ECE697F: Special Topics-Internet Routing

  5. Dynamic Routing Algorithms • Global or Link state algorithm • Use global knowledge about topology and cost • Decentralized or Distance Vector algorithm • Use only knowledge of attached links and neighbors • Distributed and iterative algorithm ECE697F: Special Topics-Internet Routing

  6. Global or Link State Algorithm • Dijkstra’s shortest path algorithm • Implementation: • Each node broadcast its connectivity and link costs to all nodes ECE697F: Special Topics-Internet Routing

  7. A A A A D D D D B B B B C C C C 2+e 2+e 0 0 1 1 1+e 1+e 0 e 0 0 Link State Algorithm Issues • Scalability • Link cost is traffic carried: can cause route oscillation 1 1+e 0 2+e 0 0 0 0 e 0 1 1+e 1 1 …recompute … recompute e initially …recompute ECE697F: Special Topics-Internet Routing

  8. Decentralized or Distance Vector Algorithm • each node communicates only with directly-attached neighbors • compute shortest path • continues until no nodes exchange information • nodes need not exchange info/iterate in lock step! ECE697F: Special Topics-Internet Routing

  9. Distance Vector Algorithm Issues • Robustness: • node can advertise incorrect path cost • each node’s table used by others • error propagate thru network • may have routing loops • Convergence Times: • count-to-infinity problem ECE697F: Special Topics-Internet Routing

  10. Evolution of the Internet 1986-1995 Regional Backbone Regional Backbone Campus Network NSFNET Backbone Regional Backbone Regional Backbone ECE697F: Special Topics-Internet Routing

  11. Internet Today NSFNET decommissioned in 1995: commercialization of the Internet (Inter)National Provider NAP Private Peering Regional Provider (Inter)National Provider ECE697F: Special Topics-Internet Routing

  12. Network Access Point (NAP) • MAE-East • MAE-West • Sprint NAP AT&T MCI FDDI Ring vBNS ECE697F: Special Topics-Internet Routing

  13. Private Peering Exchange Traffic AT&T MCI ECE697F: Special Topics-Internet Routing

  14. Internet Architecture • Segregated to Autonomous Systems (ASes) belong to • ISPs • Companies • Universities • One ISP might own several ASes • ISP Merger ECE697F: Special Topics-Internet Routing

  15. Inter-AS and Intra-AS Routing AS2 AS1 Inter-AS routing Intra-AS routing ECE697F: Special Topics-Internet Routing

  16. Why different Inter-AS and Intra-AS routing protocols? • Administrative: each AS runs different intra-AS routing protocol • Policy: AS has commercial agreement that determines routing policy • Scalability or hierarchy: hiding information within AS reduce the routing message size. ECE697F: Special Topics-Internet Routing

  17. Forwarding Table Inter-AS Routing Routing Table Intra-AS Routing ECE697F: Special Topics-Internet Routing

  18. Inter-AS Routing Protocols • Use EGP in NSFNET • Border Gateway Protocol (BGP) • BGP-4: de facto standard • Distance Vector Algorithm ECE697F: Special Topics-Internet Routing

  19. Intra-AS Routing • Routing Information Protocol (RIP) • Distance Vector Algorithm • Open Shortest Path First (OSPF) • Link State Algorithm • IS-IS • Link State Algorithm ECE697F: Special Topics-Internet Routing

  20. Exchange reachability information • Apply local policies for announcing and selecting route • Avoid Route Loops • Incremental Update • Use TCP Border Gateway Protocol (BGP) AS701 (1), (7018,1) MCI AS7018 AS1 (1), (701, 1) d AT&T BBN ECE697F: Special Topics-Internet Routing

  21. OSPF • Hierarchy: • Divided into Areas • Load balancing: • Multiple same-cost paths • Security: • Authenticate update messeges ECE697F: Special Topics-Internet Routing

  22. Where do link costs and routing policies come from? • Someone’s head • Manually entered • Router Configuration • Cause failure ECE697F: Special Topics-Internet Routing

  23. Routing Protocol Issues • Stability • Policy Effect • Congestion Effect • Protocol Design Effect • Keep Alive Message • Redundant Incremental Update message • ? • Reliability or Robustness • Alternate or Backup route • Congestion Effect • Human Error ECE697F: Special Topics-Internet Routing

  24. More Issues • Convergence Speed • Security • Scalability • Hierarchy • Traffic Engineering • Load Balancing • Qos • ? ECE697F: Special Topics-Internet Routing

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