Virtual Router Redundancy Protocol version 3 (VRRPv3) supports IPv6, but previous versions of VRRP do not. VRRP enables a group of routers to appear like a single default gateway. VRRPv3 uses the IPv4 or IPv6 address of a physical interface on the master virtual router, which is the router in the group with the highest VRRP priority. The other routers in the group are backup virtual routers. If the master virtual router fails, the backup virtual router with the highest priority will assume the role of the master virtual router, thereby providing uninterrupted service for the network. When the original master virtual router comes back online, it reestablishes its role as the master virtual router.
VRRPv3 is a standards based protocol, but so are previous versions of VRRP. VRRPv1 is defined in Request for Comments (RFC) 2338. VRRPv2 is defined in RFC3768. VRRPv3 is defined in RFC 5798.
Previous versions of VRRP included support for authentication, but VRRPv3 as defined in RFC 5798 does not include support for authentication. Cisco's implementation of VRRP supports plaintext and Message Digest 5 (MD5) authentication. When a router receives a VRRP packet for its VRRP group, it validates the authentication string. If the authentication string does not match the string that is configured on the router, the VRRP packet is discarded. When plaintext authentication is configured, the authentication string is sent unencrypted. When MD5 authentication is configured, each VRRP packet is sent with a keyed MD5 hash of that packet? if the receiving device does not generate the same hash, the packet is ignored.
Neither VRRPv3 nor previous versions of VRRP support multiple master virtual routers. All versions of VRRP allow only a single device to become the master virtual router for a group. Therefore, a VRRP group cannot be configured to use multiple devices in a load-balancing configuration.