VRRP packets are used to advertise the priority and status of the master router to all backup routers in the same VRRP backup group as the master. A VRRP packet is a multicast packet that can be forwarded only within a single broadcast domain, such as a virtual local area network (VLAN) or a virtual switching instance (VSI).
VRRP versions include VRRPv2 and VRRPv3. VRRPv2 applies only to IPv4 networks, and VRRPv3 applies to both IPv4 and IPv6 networks. VRRP is classified as VRRP for IPv4 (VRRP4) or VRRP for IPv6 (VRRP6) by network type. VRRP4 supports both VRRPv2 and VRRPv3, and VRRP6 supports only VRRPv3.
For an IPv4 network, VRRP packets are encapsulated into IPv4 packets and sent to an IPv4 multicast address assigned to a VRRP4 backup group. In an IPv4 packet header:
- The source address is the primary IPv4 address of the interface that sends the packet.
- The destination address is 224.0.0.18.
- The time to live (TTL) value is 255.
- The protocol number is 112.
For an IPv6 network, VRRP packets are encapsulated into IPv6 packets and sent to an IPv6 multicast address assigned to a VRRP6 backup group. In an IPv6 packet header:
- The source address is the link-local address of the interface that sends the packet.
- The destination address is FF02::12.
- The hop count is 255.
- The protocol number is 112.
