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End stations are often configured with a static default gateway IP address. Loss of the default gateway router can have catastrophic results. Virtual Router Redundancy Protocol (VRRP), RFC 2338, is designed to eliminate this single point of failure in a routed environment by introducing the concept of a virtual IP address (transparent to users) shared between two or more routers connecting the common subnet to the enterprise network. With the virtual IP address as the default gateway on end hosts, VRRP provides a dynamic default gateway redundancy in the event of a failure.
The VRRP timer feature is new in release 3.1. Use the Hold Down Timer to modify the behavior of the VRRP failover mechanism by allowing the router enough time to detect and update the OSPF or RIP routes.
The timer delays the preemption of the master over the backup, when the master becomes available. This timer is called the Hold Down Timer, and it has a default value of 0 seconds. Nortel Networks recommends that you set all your routers to the identical number of seconds for the Hold Down Timer.
In addition, you can manually force the preemption of the master over the backup before the delay timer expires.
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