Cisco Systems 78-11741-02 manual Configuring Routing Information Protocol, IPC-199

Configuring Routing Information Protocol

This chapter describes how to configure Routing Information Protocol (RIP). For a complete description of the RIP commands that appear in this chapter, refer to the “RIP Commands” chapter of the Cisco IOS IP Command Reference, Volume 2 of 3: Routing Protocols. To locate documentation of other commands that appear in this chapter, use the command reference master index, or search online.

RIP is a relatively old but still commonly used interior gateway protocol created for use in small, homogeneous networks. It is a classical distance-vector routing protocol. RIP is documented in RFC 1058.

RIP uses broadcast User Datagram Protocol (UDP) data packets to exchange routing information. Cisco IOS software sends routing information updates every 30 seconds, which is termed advertising. If a router does not receive an update from another router for 180 seconds or more, it marks the routes served by the nonupdating router as being unusable. If there is still no update after 240 seconds, the router removes all routing table entries for the nonupdating router.

The metric that RIP uses to rate the value of different routes is hop count. The hop count is the number of routers that can be traversed in a route. A directly connected network has a metric of zero; an unreachable network has a metric of 16. This small range of metrics makes RIP an unsuitable routing protocol for large networks.

A router that is running RIP can receive a default network via an update from another router that is running RIP, or the router can source (generate) the default network itself with RIP. In both cases, the default network is advertised through RIP to other RIP neighbors.

Cisco IOS software will source the default network with RIP if one of the following conditions is met:

•The ip default-networkcommand is configured.

•The default-information originate command is configured.

•The default route is learned via another routing protocol or static route and then redistributed into RIP.

RIP sends updates to the interfaces in the specified networks. If the network of an interface network is not specified, it will not be advertised in any RIP update.

The Cisco implementation of RIP Version 2 supports plain text and Message Digest 5 (MD5) authentication, route summarization, classless interdomain routing (CIDR), and variable-length subnet masks (VLSMs).

For protocol-independent features, which also apply to RIP, see the chapter “Configuring IP Routing Protocol-Independent Features” in this book.

Cisco IOS IP Configuration Guide

IPC-199