Systems and methods for implementing a bidirectional multicast protocol with two types of join messages are disclosed. The two types of join messages, upstream joins and downstream joins, are used to control the Reverse Path Forwarding (RPF) interface is added to the outgoing interface list for a particular multicast group, which in turn controls when multicast packets will be forwarded to the rendezvous point. One method involves receiving a multicast packet addressed to multicast group G. The method inhibits the multicast packet from being forwarded via the RPF interface, unless the outgoing interface list corresponding to the multicast group G already identifies the RPF interface. The RPF interface can be added to the outgoing interface list in response to reception of a downstream join message via the RPF interface, as well as in response to monitoring, via the RPF interface, an upstream join message on a shared network segment.