Igmp Snooping Proxying - HP A8800 Configuration Manual

A device does not forward an IGMP report through a non-router port. If the device forwards a report
message through a member port, the IGMP report suppression mechanism causes all the attached hosts
that monitor the reported multicast address suppress their own reports. This makes the device 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
When receiving a leave message
When an IGMPv1 host leaves a multicast group, the host does not send an IGMP leave message, and the
device cannot know immediately that the host has left the multicast group. However, because the host
stops sending IGMP reports as soon as it leaves the multicast group, the device removes the port that
connects to the host from the forwarding entry for the multicast group when the aging timer for the port
expires.
When an IGMPv2 or IGMPv3 host leaves a multicast group, the host sends an IGMP leave message to
the multicast router.
When the device receives an IGMP leave message on a dynamic member port, the device 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
•
port, the device directly discards the IGMP leave message.
If a forwarding entry matches the group address and the forwarding entry contains the port, the
•
device forwards the leave message to all router ports in the VLAN. Because the device does not
know whether any other hosts attached to the port are still listening to that group address, the
device 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 device forwards it through all its
router ports in the VLAN and all member ports of the multicast group. The device 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
•
group-specific query before its aging timer expires, it indicates that some host attached to the port
is receiving or expecting to receive multicast data for the multicast group. The device 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
•
expires, it indicates that no hosts attached to the port are still listening to that group address. The
device 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.
"Configuring
17
IGMP."