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Internet Routing Review: Maximizing Router Performance and Efficiency

rahim-pennington avatar
rahim-pennington
22 diapositives · 323 Views · Nov 08, 2014

Learn about graph theory, interior and exterior routing protocols, Dijkstra's algorithm, Bellman-Ford algorithm, RIP, OSPF, BGP, and more to optimize Internet routing efficiency and quality of service.

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  1. Chapter 14-16a Internet Routing Review

  2. Introduction • Motivation: Router performance is critical to overall performance and QoS in the Internet and private internetworks. Consider: • selecting best routes (optimize delay, load) • maintaining routing tables (router overhead) • router-generated management traffic • Topics: • Overview of Graph Theory • Interior Routing Protocols • Exterior Routing Protocols Chapter 14-16: Internet Routing Review

  3. Network Links Network Nodes Graph Theory and Networks Size of G: |E| = 10 Order of G: |V| = 6 Chapter 14-16: Internet Routing Review

  4. Graph Theory and Networks Weighted Digraph to Represent Link Costs Chapter 14-16: Internet Routing Review

  5. Spanning Trees Chapter 14-16: Internet Routing Review

  6. Dijkstra’s Link-State Algorithm Based on breadth-first search Running time order of |V|2 Chapter 14-16: Internet Routing Review

  7. Bellman-Ford Distance Vector Algorithm Running time order of |V| x |E| Chapter 14-16: Internet Routing Review

  8. Ex: Dijkstra vs. Bellman-Ford Least-cost routing algorithms Chapter 14-16: Internet Routing Review

  9. Exterior routing between networks A and B c b b c a Host h1 A.a A.c C.b B.a Interior/Exterior Routing Protocols Host h2 b a a C B d Interior routing within network (AS) B A Interior routing within network (AS) A Chapter 14-16: Internet Routing Review

  10. Chapter 15 Interior Routing Protocols

  11. Internet Routing Example Chapter 14-16: Internet Routing Review

  12. Routing Table Fixed vs. Adaptive Routing? Chapter 14-16: Internet Routing Review

  13. Routing Information Protocol (RIP) • Distance Vector Algorithm • typically uses simple link delay count metric • Small networks • fast and simple • max hop count = 15 (RIPv1) • Adaptive • updates sent approximately every 30 seconds • links are invalidated if no update in 180 seconds • Uses UDP transport (port 520) Chapter 14-16: Internet Routing Review

  14. RIP Messages • Command • 1 for request • 2 for reply • Version • 1: RIPv1, RFC 1058 • 2: RIP-2, RFC 1723 • Address Family ID • always 2 for IP addresses • IP address • non-zero network portion • zero host portion • Cost Metric • typically 1 (i.e. hop count) Chapter 14-16: Internet Routing Review

  15. Open Shortest Path First Protocol (OSPF) • Link-State Algorithm • Dijkstra’s Algorithm • uses flooding to advertise, request info • Preferred for TCP/IP-based internets • scale, TOS, hierarchy of areas, etc. • multiple metrics… monetary cost, reliability, throughput, delay, arbitrary • Adaptive • routers flood with new data when a significant change occurs • Sent as payload in IP datagram Chapter 14-16: Internet Routing Review

  16. Open Shortest Path First Protocol (Scale, Hierarchy) Chapter 14-16: Internet Routing Review

  17. OSPF Messages • Version • 2: current version • Type • 1: “Hello”, for discovery • 2: database structure • 3: request link-state • 4: update link-state • 5: acknowledge update • Length of message • Router ID • unique in a single area • Area ID • unique to an AS • Internet checksum • Authentication Info • Type of authentication • 64 bit authentication value OSPF Header Chapter 14-16: Internet Routing Review

  18. Chapter 16a Exterior Routing Protocols

  19. Exterior Routing OSPF BGP RIP Chapter 14-16: Internet Routing Review

  20. Border Gateway Protocol (BGP-4) • Path Vector Algorithm • cost metrics not used or advertised • each router specifies a complete path to all other nodes (e.g., from node A to node Z = ADFHKXZ) • Facilitates routing based on policyinstead of cost metrics • use preferred routes, providers (based on policy) • avoid competitors, poor performers, etc. • Adaptive • peers exchange updates on demand • nodes may choose not to participate • Uses TCP transport (port 179) Chapter 14-16: Internet Routing Review

  21. legend: B provider network X W A customer network (Stub AS) C Y Border Gateway Protocol Example • W, X, Y, A, B and C are networks • Paths are specified as, for example: • Path (w, y) = wACy • Path (x, y) = xCy • BGP routers advertise (update) only those routes that are specified by administrative policy • would A advertise …ABx… or …ACx… ? Chapter 14-16: Internet Routing Review

  22. BGP Messages Common Attributes • Marker • synchronization and authentication mechanism • Length of message • Type • open: establish a neighbor relationship • update: send/withdraw route information • keepalive: acknowledge or confirm relationship • notification: error detected Chapter 14-16: Internet Routing Review