H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 14)

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• If the forwarding table entry exists and the outgoing port list contains the port, forwards the leave
message to all router ports in the native VLAN. Because the Layer 2 device does not know whether
any other hosts attached to the port are still listening to that group address, the Layer 2 device 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.
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 Layer 2 device
forwards it through all its router ports in the VLAN and all member ports for that multicast group. The
Layer 2 device also performs the following judgment on the port that received the IGMP leave message:
• If the port (assuming it is a dynamic member port) receives any IGMP report in response to the
group-specific query 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 Layer 2 device resets
the aging timer of the port.
• If the port receives no IGMP report in response to the group-specific query before its aging timer
expires, this means that no hosts attached to the port are still listening to that group address: the
Layer 2 device removes the port from the outgoing port list of the forwarding table entry for that
multicast group when the aging timer expires.
IGMP snooping proxying
You can configure the IGMP snooping proxying function on an edge device to reduce the number of
IGMP reports and leave messages sent to its upstream device. The device configured with IGMP
snooping proxying is called an IGMP snooping proxy. It is a host from the perspective of its upstream
device.
NOTE:
Even though an IGMP snooping proxy is a host from the perspective of its upstream device, the IGMP
membership report suppression mechanism for hosts does not take effect on it.