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performs corresponding actions on the receiving port (resets/enables the age timer). A switch does not forward an
IGMP membership report through a non-router port.
When receiving a leave message
When an IGMPv1 host leaves a multicast group, the host does not send an IGMP leave message, so the switch
cannot know immediately that the host has left the multicast group. However, as the aging timer on the member
port that corresponds to the host expires, the switch immediately deletes its forwarding entry from the forwarding
table.
When an IGMPv2 or IGMPv3 host leaves a multicast group, it sends an IGMP leave message to the multicast
router to inform of such leave.
When receiving an IGMP leave message from the last member port, the switch forwards it through all router ports
in the VLAN and resets the aging timer on the receiving port (the port that received the IGMP leave message)
instead of immediately deleting its corresponding forwarding entry from the forwarding table as it cannot know
whether there are still other members of that multicast
group attached to such port.
After 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. After 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.
The switch also performs the following actions on the port that received the IGMP leave message: If the port
receives any IGMP membership report in response to the group-specific query before the aging timer expires, the
switch considers that some host attached to the port is receiving or expecting to receive multicast data from that
multicast group and will reset the aging timer on the port.
If the port receives no IGMP membership report in response to the group-specific query before its aging timer
expires, the switch considers that no hosts attached to the port are still members of that multicast group address and
thus removes the multicast forwarding entry that the port corresponds to from the forwarding table when the aging
timer expires.
IGMP Snooping
Click
Device Management > IGSP > IGMP Snooping
to enter the IGMP Snooping settings page as below:
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