Protocol Independent Multicast-Source-Specific Multicast (PIM-SSM) enables a user to specify a multicast source that will send data to a desired group. PIM-SSM is implemented based on some PIM-SM technologies. In PIM-SSM, no Rendezvous Point (RP) needs to be maintained and a dedicated multicast forwarding path is set up between a receiver and a specified multicast source.
PIM-SSM uses only some PIM-SM technologies. In PIM-SSM, it is unnecessary to maintain an RP, build a rendezvous point tree (RPT), or register a multicast source. The Designated router (DR) is valid only on a shared network segment connected to group members. Based on users' requirements, the receiver's DR sends a Join message towards the multicast source. The Join message is transmitted upstream hop by hop, and an (S, G) entry is created on each hop. An SPT is built from the router directly connected to the multicast source to the receiver's DR.
To implement PIM-SSM, the following conditions must be met:
The IPv6 multicast group that users join is in the SSM group address range.
Users specify the source when joining an IPv6 multicast group.
routers run PIM-SM.
A network can adopt both the PIM-SM and PIM-SSM models. After configuring IPv6 PIM-SM on the network, you can adjust the SSM group address range as needed. If an IPv6 multicast group that a user wants to join is not in the SSM group address range, PIM-SM is adopted to forward IPv6 multicast packets.