Chapter 5. Routing Information Protocol (RIP)

• Operation of RIP

  RIP Timers and Stability Features

  RIP Message Format

  Request Message Types

  Classful Routing

• Configuring RIP

  Case Study: A Basic RIP Configuration

  Case Study: Passive Interfaces

  Configuring Unicast Updates

  Case Study: Discontiguous Subnets

  Case Study: Manipulating RIP Metrics

• Troubleshooting RIP

The oldest of the distance vector IP routing protocols still in widespread use, RIP currently exists in two versions. This chapter deals with version 1 of RIP. Chapter 7, "Routing Information Protocol Version 2," covers version 2, which adds several enhancements to RIPv1. Most notably, RIPv1 is a classful routing protocol, whereas RIPv2 is classless. This chapter introduces classful routing, and Chapter 7 introduces classless routing.

Distance vector protocols, based on the algorithms developed by Bellman, ^[1] Ford, and Fulkerson, ^[2] were implemented as early as 1969 in networks such as ARPANET and CYCLADES. In the mid-1970s Xerox developed a protocol called PARC ^[3] Universal Protocol, or PUP, to run on its 3Mbps experimental predecessor to modern Ethernet. PUP was routed by the Gateway Information Protocol (GWINFO). PUP evolved into the Xerox Network Systems (XNS) protocol suite; concurrently, the Gateway Information Protocol became the XNS Routing Information Protocol. In turn , XNS RIP has become the precursor of such common routing protocols as Novell's IPX RIP, AppleTalk's Routing Table Maintenance Protocol (RTMP), and, of course, IP RIP.

^[1] R. E. Bellman. Dynamic Programming. Princeton, New Jersey: Princeton University Press; 1957.

^[2] L. R. Ford Jr. and D. R. Fulkerson. Flows in Networks. Princeton, New Jersey: Princeton University Press; 1962.

^[3] Palo Alto Research Center.

The 4.2 Berkeley Software Distribution of UNIX, released in 1982, implemented RIP in a daemon called routed ; many more recent versions of UNIX are based on the popular 4.2BSD and implement RIP in either routed or gated . ^[4] Oddly enough, a standard for RIP was not released until 1988, after the protocol was in extensive deployment. That was RFC 1058, written by Charles Hedrick, and it remains the only formal standard of RIPv1.

^[4] Pronounced "route-dee" and "gate-dee."

Depending on the literature one reads, RIP is either unjustly maligned or undeservedly popular. Although it does not have the capabilities of many of its successors, its simplicity and widespread use mean that compatibility problems between implementations are rare. RIP was designed for smaller internetworks in which the data links are fairly homogeneous. Within these constraints, and especially within many UNIX environments, RIP will continue to be a popular routing protocol.