What is IP Routing?
The purpose of the different IP Routing protocols and how they work.
Routing protocols implement algorithms that tell routers the best paths through internetworks. Routing protocols include Border Gateway Protocol (BGP), Interior Gateway Routing Protocol (IGRP), Routing Information Protocol, and Open Shortest Path First (OSPF) to name a few. Routing protocols provide the layer 3 network state update. Protocols that are transported through a network, such as Internet Protocol (IP), Novell Internetwork Packet eXchange (IPX), and AppleTalk are called routed protocols.
In short, routing protocols route datagrams through a network. Routing is a layer 3 function, thus, routing and routed protocols are network-layer entities. Routing tables on the layer 3 switch (router) are populated by information from routing protocols. A routed protocol will enter an interface on a router, be placed in a memory buffer, then it will be forwarded out to an interface based on information in the routing table.
Routing tables are critically important to the routing process. It is possible for these tables to be manually maintained by network administrators, but this is tedious, time-consuming and doesn't allow routers to deal with changes or problems in the internetwork. Instead, most modern routers are designed with functionality that lets them share route information with other routers, so they can keep their routing tables up to date automatically. This information exchange is accomplished through the use of routing protocols.
Note:-Some of the protocols in this section are generic enough that they could be applied to support the routing of any network layer protocol. They are most often associated with IP, however, as TCP/IP is by far the most popular internetworking protocol suite, and that is my assumption in describing them. Also, this section focuses primarily on the routing protocols used in Internet Protocol version 4. There is limited discussion of IPv6 versions of the protocols at this time.
Reference:
-dataconnection
-TCP/IP Guide
-O'Reilly
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