A method and apparatus for routing multicast data across multiple multicast routing domains connected by a shortest path bridging (SPB) network is presented. A Shortest Path Bridging (SPB) edge router of an SPB network connected to a PIM network is configured as a Rendezvous Point (RP). A message is received at the RP, and in response, the RP forms a first data structure including multicast sender information. The RP floods the SPB network with a second message containing the first data structure, allocates an Identifier to the multicast stream, and sends a second data structure with sender information. An edge router with multicast receive interest responds with the second data structure with multicast receive interest information. As a result, a receiver in a second network has knowledge of devices in a first network such that multicast traffic is able to be routed between different networks connected to the SPB network.