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Poison Reverse Updates

Stability Features (contd)

Poison Reverse Updates

Larger routing loops prevented using poison reverse updates. Poison reverse update makes a router advertises it route with a cost of 15 to indicate a network cannot to reach via it. The updates are sent to remove downed route and place it in hold-down.

Most of the slow convergence problems are handled by split horizon, poison reverse, and triggered updates. However, RIP cannot increase network diameter or disseminate network bit masks needed to properly intepret routes thus it is a poor choice for modern network. An updated version of RIP, known as RIPv2, solves this problem.

RIP Version 2 (RIPv2) RIP Version 2 adds a "network mask" and "next hop address" field to the original RIP packet while remaining completely compatible with RIP. Thus RIPv2 routers can coexist with RIP routers without any problems.

The subnet mask field contains the network bit mask associated with the destination; it also allows the implementation of CIDR addressing. This will allow RIP to function in a variety of environments, which may implement variable subnet masks on a network.

The "next hop address" field provides the address of the gateway thus allowing optimization of routes in an environment which uses multiple routing protocols thus having to ability to understand other routing protocol which may provide a better route path to a destination.

Authentication is another improvement RIPv2 offers over RIP-1. It defines password authentication mechanism for RIPv2 routers to prevent accidental updates for misconfigured hosts.

In addition to the above, RIPv2 uses multicasting instead of broadcast to reduce the load on systems that do not want RIPv2 updates and for sharing information which RIP-1 routers will not hear. In multicasting, only a set of hosts listening on a specific IP multicast address will hear the information.

Other remaining fields like routing domain and route tag are presently still limited in usage.

Routing Information Protocol, Routing Table Format
Routing Table Format, Stability Features - Hop-Count Limit
Stability Features - Hop Count Limits, Hold-Downs, Split Horizons
Stability Features - Poison Reverse Updates, RIP Version 2 (RIPv2)