R21xx-HP FlexFabric 11900 IP Multicast Configuration Guide

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• If a forwarding entry matches the group address, but the receiving port is not in the forwarding
entry for the group, the switch adds the port as a dynamic member port to the forwarding entry, and
starts an aging timer for the port.
• If a forwarding entry matches the group address and the receiving port is in the forwarding entry
for the group, the switch restarts the aging timer for the port.
In an application with an IPv6 multicast group filter configured on an MLD snooping-enabled switch,
when a user requests a multicast program, the user's host initiates an MLD report. After receiving this
report message, the switch resolves the IPv6 multicast group address in the report and looks up the ACL.
If a match is found to permit the port that received the report to join the IPv6 multicast group, the switch
creates an MLD snooping forwarding entry for the IPv6 multicast group and adds the port to the
forwarding entry. Otherwise, the switch drops this report message, in which case, the IPv6 multicast data
for the IPv6 multicast group is not sent to this port, and the user cannot retrieve the program.
A switch does not forward an MLD report through a non-router port. If the switch forwards a report
through a member port, the MLD report suppression mechanism causes all attached hosts that monitor
the reported IPv6 multicast group address to suppress their own reports. In this case, the switch cannot
determine whether the reported IPv6 multicast group still has active members attached to that port. For
more information about the MLD report suppression mechanism, see "Configuring MLD."
Done message
When a host leaves an IPv6 multicast group, the host sends an MLD done message to the multicast
routers. When the switch receives the MLD done message on a dynamic member port, the switch first
examines whether a forwarding entry matches the IPv6 multicast group address in the message, and, if
a match is found, determines whether the forwarding entry contains the dynamic member port.
• If no forwarding entry matches the IPv6 multicast group address, or if the forwarding entry does not
contain the port, the switch directly discards the MLD done message.
• If a forwarding entry matches the IPv6 multicast group address and contains the port, the switch
forwards the done message to all router ports in the VLAN. Because the switch does not know
whether any other hosts attached to the port are still listening to that IPv6 multicast group address,
the switch 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 MLD done message, the MLD querier resolves the IPv6 multicast group address in the
message and sends an MLD multicast-address-specific query to the IPv6 multicast group through the port
that received the done message. After receiving the MLD multicast-address-specific query, the switch
forwards it through all its router ports in the VLAN and all member ports of the IPv6 multicast group. The
switch also performs the following action for the port that received the MLD done message:
• If the port (assuming that it is a dynamic member port) receives an MLD report in response to the
MLD multicast-address-specific query before its aging timer expires, it indicates that some host
attached to the port is receiving or expecting to receive IPv6 multicast data for that IPv6 multicast
group. The switch adjusts the aging timer for the port.
• If the port receives no MLD report in response to the MLD multicast-address-specific query before its
aging timer expires, it indicates that no hosts attached to the port are still monitoring that IPv6