Table containing the IGMP membership information for each Multicast Group Address learned by IGMP Snooping.

With IGMP Snooping enabled,the IP DSLAM can 'listen in' on the IGMP conversation between IP Multicast Hosts and Routers, to learn the group memberships. When it hears an IGMP Join/Report from a host for a given multicast group, the IP DSLAM adds the host's MAC address to the Source MAC Address List for that group. And, when the IP DSLAM hears an IGMP Leave, it removes the host's MAC address entry.

Thus multicast traffic of a group is forwarded only to the members of that group, thereby reducing the network traffic.