PIM-Source Specific Multicast (SSM) is a one-to-many model that uses a subset of the PIM-SM features. In this model, members of an SSM group can only receive multicast traffic from a specific source or sources, which is more efficient and puts less load on multicast routing devices.
IGMPv3 supports PIM-SSM by enabling a host to selectively request traffic from individual sources within a multicast group. The system can report interest in receiving packets from only specific source addresses (INCLUDE). IGMPv3 interacts with PIM-SM, PIM-SSM, and snooping to provide source filtering.
VSP 4450 Series processes messages according to the following rules:
After IGMPv3 receives an IGMPv2 report in the SSM range, the system translates the report to an IGMPv3 report message.
After an IGMPv2 router sends queries on an IGMPv3 interface, the switch downgrades this interface to IGMPv2 (backward compatibility).
This can cause traffic interruption, but the switch recovers quickly.
Use the following information when you design an SSM network:
If you configure SSM, it affects SSM groups only. The switch handles other groups in sparse mode (SM) if a valid RP exists on the network.
You can configure PIM-SSM only on switches at the edge of the network. Core switches use PIM-SM if they do not have receivers for SSM groups.
For networks where group addresses are already in use, you can change the SSM range to match the groups.
One switch has a single SSM range.
You can have different SSM ranges on different switches.
Configure the core switches that relay multicast traffic so that they cover all of these groups in their SSM range, or use PIM-SM.
One group in the SSM range can have multiple sources for a given SSM group.