To signal that it is still in service, the master interface or vif sends “heartbeat” packets called “advertisements” to the LAN segment, using the IANA assigned multicast addresses for VRRP (224.0.0.18 for IPv4 and FF02:0:0:0:0:0:0:12 for IPv6). These advertisements confirm the health of the master router to backup routers and contain other VRRP information, such as the priority of the master.

If the backup routers do not receive advertisements from the VRRP master router for three advertisement intervals, the master is declared out of service and the VRRP protocol triggers the failover process.