H3C Technologies H3C S7500E Series Switches - Manual (Page 37)

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z If the receiving port is a dynamic router port existing in its router port list, the switch resets
the aging timer of this dynamic router port.
z If the receiving port is not a dynamic router port existing in its router port list, the switch
adds it into its router port list and sets an aging timer for this dynamic router port.
When receiving a membership report
A host sends an IGMP report to the IGMP querier 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 IGMP querier
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 reported multicast group, and performs the following:
z If no forwarding table entry exists for the reported group, the switch creates an entry, adds
the port as a dynamic member port to the outgoing port list, and starts a member port aging
timer for that port.
z If a forwarding table entry exists for the reported group, but the port is not included in the
outgoing port list for that group, the switch adds the port as a dynamic member port to the
outgoing port list, and starts an aging timer for that port.
z If a forwarding table entry exists for the reported group and the port is included in the
outgoing port list, which means that this port is already a dynamic member port, the switch
resets the aging timer for that port.
A switch does not forward an IGMP report through a non-router port. This is because if the
switch forwards a report message through a member port, all the attached hosts listening to the
reported multicast address will suppress their own reports upon receiving this report according
to the IGMP report suppression mechanism on them, and this will prevent the switch from
knowing whether the reported multicast group still has active members attached to that port.
For the IGMP report suppression mechanism on hosts, refer to IGMP Configuration in the IP
Multicast Configuration Guide.
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 dynamic 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.