10.9 Summary

There are two basic types of routing protocols: interior gateway protocols (IGPs), for routers within an autonomous system, and exterior gateway protocols (EGPs), for routers to communicate with routers in other autonomous systems.

The most popular IGP is the Routing Information Protocol (RIP) with OSPF being a newer IGP that is gaining widespread use. A new and popular EGP is the Border Gateway Protocol (BGP). In this chapter we looked at RIP and the types of messages that it exchanges. RIP Version 2 is a recent enhancement that supports subnetting and other minor improvements. We also described OSPF, BGP, and classless interdomain routing (CIDR), a newer technique being deployed to reduce the size of the Internet routing tables.

There are a two other OSI routing protocols that you may encounter. Interdomain Routing Protocol (IDRP) started out as a version of BGP modified for use with OSI addresses instead of IP. Intermediate System to Intermediate System Protocol (IS “IS) is the OSI standard IGP. It is used for routing CLNP (Connectionless Network Protocol), an OSI protocol similar to IP. IS-IS and OSPF are similar.

Dynamic routing is still a fertile area of internetworking research. The choice of which routing protocol to use, and which routing daemon to run, is complex. [Perlman 1992] provides many of the details.