Configuring Layer 3 Redundancy with Virtual Router Redundancy Protocol – VRRP and Gateway Load Balancing Protocol – GLBP
Identifying the VRRP operations process

This figure shows a LAN topology in which VRRP is configured so that routers A and B share the load of being the default gateway for clients 1 through 4. Routers A and B act as backup virtual routers to one another should either router fail.

In this example, two virtual routers groups are configured. For virtual router 1, router A is the owner of IP address 10.0.0.1, and therefore, the master virtual router for clients configured with that default gateway address. Router B is the backup virtual router to router A.

For virtual router 2, router B is the owner of IP address 10.0.0.2 and is the master virtual router for clients configured with the default gateway IP address of 10.0.0.2. Router A is the backup virtual router to router B.

Given that the IP address of the VRRP group is that of a physical interface on one of the group members, the router owning that address will be the master in the VRRP group. Its priority is set to 255. Backup router priority values can range from 1 to 254; the default value is 100.

The master sends the advertisement on multicast 224.0.0.18 on a default interval of 1 second. A VRRP flow message is similar in concept to an HSRP coup message. A master with a priority of zero triggers a transition to a backup router. The result is similar to an HSRP resign message.

The dynamic failover, when the active (master) becomes unavailable, uses two timers within VRRP: the advertisement interval and the master-down interval. The advertisement interval is the time interval between advertisements (seconds). The default interval is 1 second. The master-down interval is the time interval for backup to declare the master down (seconds).