Processing Of Multicast Protocol Messages; Protocols And Standards - HP 4800G Series Configuration Manual

does not immediately remove the port from the outgoing port list of the forwarding table entry for
that group; instead, it resets the aging timer for the port.
Upon receiving the IGMP leave message from a host, the IGMP querier resolves the multicast group
address in the message and sends an IGMP group-specific query to that multicast group through the
port that received the leave message. Upon receiving the IGMP group-specific query, the switch
forwards it through all its router ports in the VLAN and all member ports for that multicast group, and
performs the following to the port on which it received the IGMP leave message:
If any IGMP report in response to the group-specific query is received on the port (suppose it is a
dynamic member port) before its aging timer expires, this means that some host attached to the
port is receiving or expecting to receive multicast data for that multicast group. The switch resets
the aging timer of the port.
If no IGMP report in response to the group-specific query is received on the port before its aging
timer expires, this means that no hosts attached to the port are still listening to that group address:
the switch removes the port from the outgoing port list of the forwarding table entry for that
multicast group when the aging timer expires.

Processing of Multicast Protocol Messages

With Layer 3 multicast routing enabled, an IGMP Snooping switch processes multicast protocol
messages 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 handles
multicast protocol messages in the normal way.
2) In only PIM is enabled on the switch:
The switch broadcasts IGMP messages as unknown messages in the VLAN.
Upon receiving a PIM hello message, the switch will maintain the corresponding dynamic router
port.
3) When IGMP is disabled on the switch:
If PIM is disabled, the switch deletes all its dynamic member ports and dynamic router ports.
If PIM is enabled, the switch deletes only its dynamic member ports without deleting its dynamic
router ports.
On a switch with Layer-3 multicast routing enabled, use the display igmp group port-info command to
view Layer-2 port information.
For details about the display igmp group port-info command, refer to IGMP Commands in the IP
Multicast Volume.
4) When PIM is disabled on the switch:
If IGMP is disabled, the switch deletes all its dynamic router ports.
If IGMP is enabled, the switch maintains all its dynamic member ports and dynamic router ports.

Protocols and Standards

IGMP Snooping is documented in:
1-5