In a multicast network, which condition must be met for an RPF check to be performed on the RP address?

If a PIM router has a source-tree state ((S, G) state), it means it has switched to the shortest path tree directly to the source (S), and in this case, the RPF check is performed against the *source's* address, not the RP's address.

This scenario describes a behavior in PIM Dense Mode (PIM-DM), where a router with no directly connected members would prune traffic, but it does not specify the condition for an RPF check on the RP address.

This scenario describes a condition in PIM Dense Mode where a router might flood or prune, but it is not the specific condition for performing an RPF check on the RP address, which is characteristic of PIM-SM shared-tree operation.

In PIM Sparse Mode (PIM-SM), when a router is on the shared tree (*, G) for a multicast group, it forwards multicast traffic received from the RP. To prevent loops and ensure the traffic is coming from the shortest path towards the RP, the router performs an RPF check against the RP's address. If the incoming interface is not the shortest path back to the RP, the packet is dropped.