Igmp Snooping Proxying - HP MSR ASM Configuration Manual

suppression mechanism causes all attached hosts that monitor the reported multicast address to suppress
their own reports. This makes this router unable to know whether the reported multicast group still has
active members attached to that port. For more information about the IGMP report suppression
mechanism, see "Configuring IGMP."
When receiving a leave message
An IGMPv1 host silently leaves a multicast group and the IGMP snooping-enabled router is not notified
of the leave. However, because the host stops sending IGMP reports after it leaves the multicast group,
the aging timer for the port that connects to the host expires. Once the aging timer expires, the IGMP
snooping-enabled router removes the port from the forwarding entry for the multicast group.
An IGMPv2 or IGMPv3 host sends an IGMP leave message to the multicast router when leaving a
multicast group.
When the IGMP snooping-enabled router receives an IGMP leave message on a dynamic member port,
this router first examines whether a forwarding entry matches the group address in the message, and, if
a match is found, whether the forwarding entry for the group contains the dynamic member port.
If no forwarding entry matches the group address, or if the forwarding entry does not contain the
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port, the IGMP snooping-enabled router directly discards the IGMP leave message.
If a forwarding entry matches the group address and the forwarding entry contains the port, the
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IGMP snooping-enabled router forwards the leave message to all router ports in the VLAN. Because
the IGMP snooping-enabled router does not know whether any other hosts attached to the port are
still listening to that group address, it does not immediately remove the port from the forwarding
entry for that group. Instead, it restarts the aging timer for the port.
After receiving the IGMP leave message, the IGMP querier resolves the multicast group address in the
message and sends an IGMP group-specific query to the multicast group through the port that received
the leave message. After receiving the IGMP group-specific query, the IGMP snooping-enabled router
forwards it through all its router ports in the VLAN and all member ports of the multicast group. This router
also performs the following judgment for the port that received the IGMP leave message:
If the port (assuming that it is a dynamic member port) receives an IGMP report in response to the
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group-specific query before its aging timer expires, it means that some host attached to the port is
receiving or expecting to receive multicast data for the multicast group. The IGMP
snooping-enabled router restarts the aging timer for the port.
If the port receives no IGMP report in response to the group-specific query before its aging timer
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expires, it means that no hosts attached to the port are still listening to that group address. The
IGMP snooping-enabled router removes the port from the forwarding entry for the 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.
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 affect it. For more information about the
IGMP report suppression mechanism for hosts, see "Configuring IGMP."
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