ABSTRACT
Routing is the process of computing possible paths between the nodes in a ne work. Routing is a function of the network layer, yet many routing protocols in the Internet depend on transport layer protocols for the communication of their control packets. Typically, routing is performed by core nodes in the network, called routers, which store path information in their routing tables. To keep the routing process scalable given the immense size of the Internet, the Internet is partitioned into smaller groups of routers and networks. Each such partition is managed by a single authority, which denes administrative rules and routing policies, and is called an Autonomous System (AS). A wide variety of routing protocols is deployed in the Internet today as each AS can independently decide which routing protocol to employ within its connes. Protocols used within an AS are known as intra-AS routing protocols. On the other hand, inter-AS routing protocols are responsible for maintaining routing information for data delivery between ASs. OPNET supports many common intra-AS protocols including RIP, RIPng, OSPF, OSPFv3, EIGRP, IGRP, and IS-IS. OPNET also implements BGP, an inter-AS routing protocol. We only describe two intra-AS protocols, RIP and OSPF, in this chapter. The other intra-AS protocols and BGP are beyond the scope of this book and are not discussed here.
