In PIM Source-Specific Multicast (PIM-SSM), which uses a subset of PIM-SM and Multicast Listener Discovery (MLD) v2, a hosts receives multicast traffic directly from the source.
PIM-SSM uses PIM-SM functionality to create a Shortest Path Tree (SPT) between the receiver and the source without the help of a rendezvous point (RP).
In a PIM-SSM network, a host subscribes to an SSM channel (by means of MLDv2) and sends a request to join group G and source S. The directly connected PIM-SM router, the receiver's designated router (DR), sends an (S,G) Join message to its reverse path forwarding (RPF) neighbor for the source. The receiver doesn't contact the RP in this process, unlike standard PIM-SM operations. The (S,G) Join message initiates the source tree and then builds it, hop by hop, toward the source. Multicast traffic is delivered to the subscribing host by way of the source tree.
The default IPv6 SSM group range is FF3x::/32, where x is one of the following valid
values: 4, 5, 8, E.