Unicast Support for the Virtual Router Redundancy Protocol (VRRP)

The Virtual Router Redundancy Protocol (VRRP) is specified for multicast operation on a shared LAN in RFC 9568. Some deployments, including virtualized and cloud environments, require VRRP-like first-hop redundancy but cannot use multicast delivery for VRRP advertisements. This document updates RFC 9568 by defining an optional unicast mode for VRRP. In unicast mode, VRRP advertisements are sent to configured peer addresses rather than to the VRRP multicast group. This document preserves the VRRP packet format, protocol number, virtual IP semantics, and host-facing forwarding behavior defined in RFC 9568, while adding explicit peer configuration and receive-side source validation for unicast operation.