1-7IGMP message ActionsReportWhen receiving a report for a multicast group, the proxy looks up the multicastforwarding table for the entry for the multicast group. If the forwarding entry isfound with the receiving port contained as a dynamic member port in the outgoingport list, the proxy resets the aging timer for the entry. If the forwarding entry isfound but the outgoing port list does not include the receiving port, the proxy addsthe port to the outgoing port list as a dynamic member port and starts an agingtimer for it. If no forwarding entry is found, the proxy creates the entry, adds thereceiving port to the outgoing port list as a dynamic member port and starts anaging timer for the port, and then, sends a report to the group out all router ports.LeaveIn response to an IGMP leave message for a multicast group, the proxy sends agroup-specific query out the receiving port. After making sure that no memberport is contained in the forwarding entry for the multicast group, the proxy sends aleave message to the group out all router ports.Processing of Multicast Protocol MessagesWith Layer 3 multicast routing enabled, an IGMP snooping switch processes multicast protocolmessages differently under different conditions, specifically as follows:1) If only IGMP is enabled, or both IGMP and PIM are enabled on the switch, the switch handlesmulticast protocol messages in the normal way.2) In only PIM is enabled on the switch:z The switch broadcasts IGMP messages as unknown messages in the VLAN.z Upon receiving a PIM hello message, the switch will maintain the corresponding dynamic routerport.3) When IGMP is disabled on the switch:z If PIM is disabled, the switch deletes all its dynamic member ports and dynamic router ports.z If PIM is enabled, the switch deletes only its dynamic member ports without deleting its dynamicrouter ports.On a switch with Layer-3 multicast routing enabled, use the display igmp group port-info command toview Layer-2 port information.For details about the display igmp group port-info command, refer to IGMP Commands in the IPMulticast Volume.4) When PIM is disabled on the switch:z If IGMP is disabled, the switch deletes all its dynamic router ports.z If IGMP is enabled, the switch maintains all its dynamic member ports and dynamic router ports.Protocols and StandardsIGMP snooping is documented in:z RFC 4541: Considerations for Internet Group Management Protocol (IGMP) and Multicast ListenerDiscovery (MLD) Snooping Switches
