Group Registration

Multicast listeners can register to an IP multicast group by sending an IGMP (Internet Group Management Protocol) Report message in response to a general query from a multicast router or by sending an unsolicited IGMP Report message. When the snooping switch processes an IGMP Report message, it creates an entry in the Layer 2 multicast forwarding table for the requested multicast group. Each entry contains a unique VLAN and multicast group combination along with a list of ports on which the IGMP Report was received. Multicast router-attached ports discovered during query processing on the incoming VLAN are automatically added to the newly created Layer 2 multicast forwarding entry.

The created entries expire if no additional IGMP Report messages are received for that multicast group, VLAN, and received port combination. The snooping switch administrator can configure the group expiry on a per-VLAN basis. If all the host registrations expire for a Layer 2 multicast forwarding entry, the entry is removed from the table.