Reverse Path Forwarding is a method, which ensures loop-free forwarding of IP multicast packets in which hosts do not receive the packets more than once. The source address and the previously used interface in the network are crucial for forwarding the data stream. As soon as a multicast packet reaches a router interface, it compares both of these pieces of information with a routing table which was previously either automatically generated by the broadcast or configured manually. If there is an entry for the source address which confirms the previously used interface, the RPF check is successful and the router forwards the multicast stream to all other available interfaces. If not, it discards the packets.
RPF performs a reverse check of the packet’s path. Additionally, unicast routing methods are used to connect routers using the shortest possible path. The routing map is also referred to as the multicast tree. The sender or its router represents the roots (i.e. the starting point).