1-4
General queries
The MLD querier periodically sends MLD general queries to all hosts and routers (FF02::1) on the local
subnet to find out whether IPv6 multicast group members exist on the subnet.
Upon receiving an MLD general query, the switch forwards it through all ports in the VLAN except the
port on which it received the MLD query and performs the following:
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If the port on which it the switch received the MLD query is a dynamic router port in its router port
list, the switch resets the aging timer for this dynamic router port.
z
If the port is not included in its router port list, the switch adds it into its router port list as a dynamic
router port and sets an aging timer for it.
Membership reports
A host sends an MLD report to the MLD querier in the following circumstances:
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Upon receiving an MLD query, an IPv6 multicast group member host responds with an MLD report.
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When intended to join an IPv6 multicast group, a host sends an MLD report to the MLD querier to
announce that it is interested in the multicast information addressed to that IPv6 multicast group.
Upon receiving an MLD report, the switch forwards it through all the router ports in the VLAN, resolves
the address of the reported IPv6 multicast group, and performs the following to the receiving port:
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If no forwarding table entry exists for the reported IPv6 multicast 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 IPv6 multicast 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 a member port aging timer for that port.
z
If a forwarding table entry exists for the reported IPv6 multicast 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 member port aging timer for that port.
A switch does not forward an MLD report through a non-router port. The reason is as follows: Due to the
MLD report suppression mechanism applied on hosts, if the switch forwards a report message through
a member port, all the attached hosts listening to the reported IPv6 multicast address will suppress their
own reports upon receiving this report, and this will prevent the switch from knowing whether the
reported multicast group still has active members attached to that port.
Done messages
When a host leaves an IPv6 multicast group, the host sends an MLD done message to the multicast
router.
When the switch receives an MLD done message on a dynamic member port, the switch first checks
whether a forwarding table entry for the IPv6 multicast group address in the message exists, and, if one
exists, whether the outgoing port list contains the port.
