Routing Information Protocol

The Routing Information Protocol (RIP) was one of the most commonly used interior gateway protocol (IGP) routing protocols on internal networks (and to a lesser extent, networks connected to the Internet), which helps routers dynamically adapt to changes of network connections by communicating information about which networks each router can reach and how far away those networks are.

Although RIP is still actively used, it is generally considered to have been made obsolete by routing protocols such as OSPF and IS-IS. Nonetheless, a somewhat more capable protocol in the same basic family (distance-vector routing protocols), was Cisco's proprietary (IGRP) Interior Gateway Routing Protocol. Cisco does not support IGRP in current releases of its software. It was "replaced" by EIGRP, the Enhanced Interior Gateway Routing Protocol, which is a completely new design. While EIGRP is still technically distance vector, it relates to IGRP only in having a similar name.

RIP is sometimes said to stand for Rest in Pieces in reference to the reputation that RIP has for breaking unexpectedly, rendering a network unable to function.

Reference:
http://en.wikipedia.org/wiki/Routing_Information_Protocol