H3C Technologies H3C S3100 Series Switches - Manual (Page 290)

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z If the receiving port is a router port existing in its router port list, the switch resets the aging timer of
this router port.
z If the receiving port is not a router port existing in its router port list, the switch adds it into its router
port list and sets an aging timer for this router port.
When receiving a membership report
A host sends an IGMP report to the multicast router in the following circumstances:
z Upon receiving an IGMP query, a multicast group member host responds with an IGMP report.
z When intended to join a multicast group, a host sends an IGMP report to the multicast router to
announce that it is interested in the multicast information addressed to that group.
Upon receiving an IGMP report, the switch forwards it through all the router ports in the VLAN, resolves
the address of the multicast group the host is interested in, and performs the following to the receiving
port:
z If the port is already in the forwarding table, the switch resets the member port aging timer of the
port.
z If the port is not in the forwarding table, the switch installs an entry for this port in the forwarding
table and starts the member port aging timer of this port.
A switch will not forward an IGMP report through a non-router port for the following reason: Due to the
IGMP report suppression mechanism, if member hosts of that multicast group still exist under
non-router ports, the hosts will stop sending reports when they receive the message, and this prevents
the switch from knowing if members of that multicast group are still attached to these ports.
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 host
stops sending IGMP reports as soon as it leaves a multicast group, the switch deletes the forwarding
entry for the member port corresponding to the host from the forwarding table when its aging timer
expires.
When an IGMPv2 or IGMPv3 host leaves a multicast group, the host sends an IGMP leave message to
the multicast router to announce that it has leaf the multicast group.
Upon receiving an IGMP leave message on the last member port, a switch forwards it out all router ports
in the VLAN. Because the switch does not know whether any other member hosts of that multicast
group still exists under the port to which the IGMP leave message arrived, the switch does not
immediately delete the forwarding entry corresponding to that port from the forwarding table; instead, it
resets the aging timer of the member port.
Upon receiving the IGMP leave message from a host, the IGMP querier resolves from the message the
address of the multicast group that the host just left 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, a switch forwards it through all the router ports in the VLAN and all member ports
of that multicast group, and performs the following to the receiving port: