ScreenOS Cookbook

Chapter 15. RIP

15.0. Introduction

The Routing Information Protocol (RIP) is an Interior Gateway Protocol (IGP) that has been used extensively in corporate and personal networking environments for the past two decades. RIP version 2, the current specification of RIP, is defined in RFC 2453. RIP was historically specified in RFC 1723 and RFC 1388, both of which are now obsolete. The primary reason for RIP’s wide adoption has been its simplicity and wide availability. Compared to other prevailing IGPs such as the Open Shortest Path First (OSPF) and Intermediate System to Intermediate System (IS-IS) protocols, RIP is easier to implement. Also, given its simplicity, RIP has been more widely available on servers and general-purpose networking appliances when compared with other IGPs.

RIP is a distance-vector protocol based on the Bellman-Ford algorithm. Distance-vector protocols advertise the metric (or hop count) associated with a destination network to their neighboring routers. Unlike OSPF or IS-IS-speaking devices, RIP gateways do not maintain a link state database that is consistent across all the devices in an autonomous system. Instead, each device that runs RIP can send updates about the destinations that are directly defined on it or those that it has learned from neighbors.

RIP gateways rely on a single unit—the metric associated with a destination address—to make their best-path selection. Each RIP-speaking interface has a metric associated with it. When a RIP gateway receives ...