Nortel Networks 42C4911 manual RIPv2 in RIPv1 compatibility mode, RIP Features, Poison, Multicast

Alteon OS Application Guide

RIPv2 in RIPv1 compatibility mode

Alteon OS allows you to configure RIPv2 in RIPv1compatibility mode, for using both RIPv2 and RIPv1 routers within a network. In this mode, the regular routing updates use broadcast UDP data packet to allow RIPv1 routers to receive those packets. With RIPv1 routers as recip- ients, the routing updates have to carry natural or host mask. Hence, it is not a recommended configuration for most network topologies.

NOTE – When using both RIPv1 and RIPv2 within a network, use a single subnet mask throughout the network.

RIP Features

Alteon OS provides the following features to support RIPv1 and RIPv2:

Poison

Simple split horizon in RIP scheme omits routes learned from one neighbor in updates sent to that neighbor. That is the most common configuration used in RIP, that is setting this Poison to DISABLE. Split horizon with poisoned reverse includes such routes in updates, but sets their metrics to 16. The disadvantage of using this feature is the increase of size in the routing updates.

Triggered updates

Triggered updates are an attempt to speed up convergence. When Triggered Updates is enabled (/cfg/l3/rip/if x/trigg/e), whenever a router changes the metric for a route, it sends update messages almost immediately, without waiting for the regular update interval. It is recommended to enable Triggered Updates.

Multicast

RIPv2 messages use IP multicast address (224.0.0.9) for periodic broadcasts. Multicast RIPv2 announcements are not processed by RIPv1 routers. IGMP is not needed since these are inter- router messages which are not forwarded.

To configure RIPv2 in RIPv1 compatibility mode, set multicast to disable, and set version to both.

42C4911, January 2007 Chapter 9: Routing Information Protocol „ 157