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Understanding Routing Protocols: Fundamentals, Concepts, and Applications

This overview explores the critical concepts of routing in internetworking, covering the functionalities of routing and routed protocols, the principles of path determination, and the differences between distance-vector, link-state, and hybrid approaches. It discusses network and host addressing, the role of routing protocols such as RIP, IGRP, EIGRP, and OSPF, and emphasizes the necessity of dynamic routing for efficient network performance. Key aspects of static versus dynamic routes, convergence time, and routing table maintenance are also addressed, providing a comprehensive understanding of how routers manage data transfer across networks.

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Understanding Routing Protocols: Fundamentals, Concepts, and Applications

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  1. Chap 11 Routing Andres, Wen-Yuan Liao Department of Computer Science and Engineering De Lin Institute of Technology andres@dlit.edu.tw http://www.cse.dlit.edu.tw/~andres

  2. Overview • Internetworking function • Routing and routed protocols • Track distance between locations • Distance-vector, link-state, and hybrid routing approaches

  3. Routing Basics • Path determination • Route packets from source to destination • Network and host addressing • Path selection and packet switching • Routed versus routing protocol • Network-layer protocol operations • Multiprotocol routing

  4. Path determination • Evaluate the available paths to a destination and to establish the preferred handling of a packet • Network part of IP • Layer 3

  5. Route packets • The consistency of Layer 3 addr. improves the use of bandwidth by preventing unnecessary broadcasts • Broadcasts invoke unnecessary process overhead and waste capacity

  6. Network and host addressing • The router uses the network address to identify the destination network of a packet • Assigning host addresses • Network administrator • Be partially or completely dynamic

  7. Path selection and packet switching • The router uses the network portion of the address to make path selections • The switching function: accept a packet on one interface and forward it through a second interface

  8. Routed versus routing protocol • Routed protocols define the field formats within a packet (IP): Carry data • Routing protocols provide mechanisms for sharing routing information: Maintain table

  9. Routing protocol • RIP (Routing Information Protocol) • IGRP (Interior Gateway Routing Protocol) • EIGRP (Enhanced Interior Gateway Routing Protocol) • OSPF (Open Shortest Path First)

  10. Multiprotocol routing • Routers are capable of supporting multiple independent routing protocols and maintaining routing tables for several routed protocols

  11. Why Routing Protocols are Necessary • Static versus dynamic routes • Default route • Dynamic routing • Various metrics • Three classes of routing protocols • Time to convergence

  12. Static versus dynamic routes • Static route • Be administered manually by a network administrator who enters it into a router's configuration • Dynamic route • The route knowledge: updated by a routing process

  13. Static route • Dynamic routing: reveal everything known about an inter-network • Security reasons • Hide parts of an internetwork • A stub network:A network is accessible by one path

  14. Default route • A routing table entry that directs packets to the next hop when that hop is not explicitly listed in the routing table

  15. Dynamic routing • Offers more flexibility • Loadsharing • Direct traffic from the same session over different paths in a network for better performance

  16. Dynamic routing operations • Maintenance of a routing table • Timely distribution of knowledge, in the form of routing updates, to other routers

  17. A routing protocol • How to send updates • What knowledge is contained in these updates • When to send this knowledge • How to locate recipients of the updates

  18. Three classes of routing protocols • Distance-vector routing • Determines the direction (vector) and distance to any link • Link-state (shortest path first) • Re-creates the exact topology • Balanced hybrid approach

  19. Time to convergence • Convergence • The knowledge: an accurate, consistent view of new topology • Converged • All routers in an internetwork are operating with the same knowledge • Fast convergence

  20. Distance-Vector Routing • Distance-vector routing basics • Exchange routing tables • Topology changes propagate • Routing loops • Counting to infinity • Defining a maximum • Split horizon • Hold-down timers

  21. Distance-vector routing basics • Pass periodic copies of a routing table from router to router • Do not allow a router to know the exact topology of an internetwork

  22. Exchange routing tables • Directly-connected network • A distance of 0

  23. Topology changes propagate • Topology change updates proceed step-by-step from router to router • Send its entire routing table to each of its adjacent neighbor

  24. Routing loops • A network's slow convergence on a new configuration causes inconsistent routing entries

  25. Routing loops • Packets never reach their destination but instead cycle repeatedly through the same group of network nodes

  26. Counting to infinity • The invalid updates will continue to loop until some other process stops the looping

  27. Sol: Defining a maximum • Routing metric (hop count) • Distance-vector protocols define infinity as a specific maximum no. • The distance-vector default maximum of 15 hops

  28. Sol: Split horizon • Split-horizon attempts: if a routing update about Network 1 arrives from Router A, Router B or Router D cannot send information about Network 1 back to Router A

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