Which feature is used in multicast routing to prevent loops?

In IP multicast routing, each arriving multicast packet must pass the Reverse-Path Forwarding (RPF) check: the interface on which the packet is received must be the one that would be used to reach the source. Packets failing this test are dropped, preventing forwarding loops and duplicate traffic. RPF is therefore the specific loop-prevention mechanism built into all PIM multicast forwarding decisions.

A. STP prevents Layer-2 bridging loops, not IP multicast routing loops.
B. Inverse ARP only discovers Layer-2 VC mappings on NBMA networks; it is unrelated to multicast forwarding.
D. Split horizon suppresses route advertisement on the interface from which it was learned for distance-vector unicast protocols, not multicast.

1. Cisco IOS IP Multicast Technology Overview, “Reverse Path Forwarding,” Cisco.com, 15-M&T, para 2.

2. RFC 1812: Requirements for IP Routers, §5.3.7.2, Reverse Path Forwarding Check.

3. Beau Williamson, “Developing IP Multicast Networks, 2nd ed.,” Cisco Press, pp. 61-63.