The VRRP router that controls the IP addresses associated with a virtual router is considered to be in the master state, is the active router for the VRRP instance, and is responsible for forwarding packets sent to the VRRP IP address. An election process provides dynamic failover of the forwarding responsibility if the master becomes unavailable. In such an event, any of the virtual router IP addresses on the LAN can be used as the default first hop router by end-hosts. This capability enables a higher availability default path without requiring configuration of dynamic routing or router discovery protocols on every end host.
If the active router is unavailable, each backup virtual router for the VRID compares the configured priority values to determine the master role. In case of a tie, the virtual router with the highest primary IP address becomes master.
Setting the preempt parameter to false prevents a backup virtual router configured with a better priority value from becoming master when an existing non-owner virtual router is the current master. This is determined on a first-come, first-served basis.
While master, a virtual router originates all IP packets and routes them into the LAN using the physical MAC address for the IP interface as the Layer 2 source MAC address, not the VRID MAC address. ARP packets also use the parent IP interface MAC address as the Layer 2 source MAC address and insert the virtual router MAC address in the appropriate hardware address field. VRRP messages are the only packets transmitted using the virtual router MAC address as the Layer 2 source MAC.