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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 current implementation of VRRP allows you to have one active master switch per IP subnet. All other VRRP interfaces in a network are in backup mode.
On a Passport 8000 Series switch, you cannot directly check or set the virtual IP address on the standby CPU module. In order to check or set the virtual IP address on the standby CPU, you must configure the virtual IP address on the master CPU, save it to the config.cfg file, and then copy that file to the standby CPU module
If you have VRRP and IP routing protocols (for example, OSPF) configured on the same IP physical interface, selecting the interface address as the VRRP virtual IP address (logical IP address) is not supported. Use a separate dedicated IP address for VRRP.
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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