Virtual Router Redundancy Protocol (VRRP) is a protocol for providing default gateway redundancy in a network. VRRP provides for a dynamic assignment of a default gateway to a single member of a set of VRRP routers that collectively act as a single virtual router with a common virtual internet protocol (IP) address. A VRRP network is a network that has two or more routers that support the VRRP protocol. Hosts or other network components use the common IP address of the VRRP routers as their default gateway.
In VRRP protocol, the router with a highest priority becomes the master gateway of the group of routers. In the role as a master gateway, a VRRP router has several tasks. One task is owning the VRRP virtual IP address and answering address resolution protocol (ARP) requests sent to the virtual IP address. The master gateway also associates the virtual IP address with the virtual media access control (MAC) address. Another task is sending VRRP advertisement packets at regular intervals to other VRRP routers in the set to let them know that the device is still functioning as the master gateway.
When the VRRP router designated as the master loses connectivity to the network, the VRRP advertisement packets no longer reach the other routers in the set. In such a situation, one of the other routers will take over as the master router in response to the discontinuation of VRRP advertisement packets. The VRRP router will also send out a gratuitous ARP request associating the virtual IP address with the virtual MAC address. This causes downstream switches to forward traffic destined to the virtual MAC address to the new VRRP master router. This task ensures that traffic to the gateway from network components in the network is not interrupted. Once accomplished, the new router will own the virtual IP address, answer ARP requests sent to the virtual IP address, and send out VRRP advertisement packets at regular intervals.