Selected Answer: D D. The PIM router or multilayer switch has a shared-tree state. In a multicast network, the Reverse Path Forwarding (RPF) check is done to make sure multicast traffic travels along the best path and to avoid loops. When a PIM router or multilayer switch is in a shared-tree state, it means it is using a shared distribution tree with a Rendezvous Point (RP) at the root. In this case, the RPF check is performed on the RP address to verify that multicast packets are being received from the correct upstream path toward the RP.

But RPF is not used with PIM-DM? Then it wouldn't be any RP nor shared-trees, but source trees. Would it be so?

Selected Answer: D D is correct. "If a PIM router has no source-tree state, it is considered a shared tree state. The router will perform a RPF check on the address of the rendezvous point – the rendezvous address is known when members join the group" https://www.routeprotocol.com/reverse-path-forwarding-rpf/

Selected Answer: D RPF is checked against the FHR when in SPT/Source tree state and against the RP when in Shared tree state