If the RPF check is successful in PIM sparse mode, the multicast packet is forwarded according to the outgoing interface list. The Reverse Path Forwarding check verifies that the packet arrived on the interface the router would use to reach the source, or the RP in the case of shared-tree state. This prevents loops and duplicate multicast forwarding. After the check passes, the router consults the multicast forwarding entry and sends the packet only out interfaces in the OIL where downstream receivers or PIM neighbors require the traffic. It is not automatically forwarded out every PIM-enabled interface, and it is not forwarded back out the receiving interface. If the RPF check fails, the packet is dropped to protect the multicast distribution tree. The OIL therefore represents the correct controlled forwarding behavior after a successful RPF validation.
Reference topics: PIM sparse mode, RPF check, outgoing interface list, multicast forwarding state, loop prevention.