This 64-bit counter tallies all multicast packets dropped on an SPB (Shortest Path Bridging) BVLAN (backbone VLAN) because they failed Reverse Path Forwarding Checks (RPFC) against the source address. RPFC is a loop-prevention mechanism that validates the packet's source is reachable from the incoming port; failed checks indicate either spoofed sources or network topology inconsistencies. A network operator investigating multicast traffic loss, potential spoofing attacks, or SPB path misconfiguration would examine this counter to determine if RPFC is legitimately blocking unwanted traffic or indicating a network problem.