This read-only object specifies the network prefix length (in bits) of the routing table entry used to determine the reverse-path forwarding (RPF) interface toward the Rendezvous Point (RP) for multicast group traffic. Combined with the corresponding pimStarGRPFRouteAddress, it identifies the exact unicast route the router uses to validate incoming multicast packets from a group. Multicast routers query this to verify their RPF calculations and troubleshoot multicast forwarding issues.