Fast failure detection in VRRP with S-BFD

The Virtual Router Redundancy Protocol (VRRP) protocol depends on IPv4 or IPv6 connectivity between redundant peers and can use Seamless Bidirectional Forwarding Detection (S-BFD) to detect a Primary Router failure faster than the base VRRP advertisement timers. This document describes an extension that allows VRRP to use S-BFD as an additional failure-detection mechanism. It defines a new VRRP packet type, a dedicated timer, and a mechanism for a VRRP Primary Router to advertise an S-BFD reflector discriminator to Backup Routers. Local discriminator allocation is left to the implementation.