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VRRP (Virtual Router Redundancy Protocol)

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In some internetwork environments, networks are connected to other networks via a single router. But that single router is a potential point of failure that can disconnect an entire network from the rest of the internetwork.

VRRP eliminates single points of failure by providing a protocol that supports redundant router connections. An added feature is the ability to do load sharing in which each redundant link carries traffic.

The protocol is designed to help reduce downtime and delays normally associated with lost links and dynamic route configuration. Redundant routers are installed and one is "elected" as the master router. If a router fails, one of the redundant "backup" routers takes over as the master router. The master router sends a special VRRP advertisement packet to the backup routers, usually every second. If advertisements stop, the backups assume the master is down and initiate backup mode, in which the next-in-line router is elected.

An important point is that VRRP provides fast, efficient recovery from failures. Dynamic routing protocols such as RIP and OSPF are time-consuming and inefficient. They must discover failed routes, alert other routers, run routing algorithms to calculate alternate routers, and then build routing tables.

Recovery is so fast in the event of a failure that most end systems may not even notice that the switching over has occurred. In addition, routers in the configuration share a virtual IP and MAC address, so that end systems see the routers as having the same address.

The following RFCs provide complete details about VRRP. You can also check the EITF VRRP Working Group Web page listed shortly for additional information.

  • RFC 2238 (Virtual Router Redundancy Protocol, April 1998)

  • RFC 2787 (Definitions of Managed Objects for the Virtual Router Redundancy Protocol, March 2000)

Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.
All rights reserved under Pan American and International copyright conventions.