H3C Technologies H3C S12500 Series Switches - Manual (Page 302)

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Timer Description
Message before
expiration
Action after expiration
Dynamic member
port aging timer.
When a port dynamically joins
a multicast group, the switch
starts or resets an aging timer
for the port. When the timer
expires, the dynamic member
port ages out.
MLD report message.
The switch removes this
port from the MLD
snooping forwarding
table.
NOTE:
In MLD snooping, only dynamic ports age out. Static ports never age out.
How MLD snooping operates
The ports in this section are dynamic ports. For information about how to configure and remove static
ports, see " Configuring static ports ."
MLD messages types are as follows: general query, MLD report, and done message. An MLD
snooping-enabled switch performs differently depending on the MLD message.
General query
The MLD querier periodically sends MLD general queries to all hosts and routers (FF02::1) on the local
subnet to find out whether any active IPv6 multicast group members exist on the subnet.
After receiving an MLD general query, the switch forwards it to all ports in the VLAN, except the port that
received the query. The switch also performs one of the following actions:
• If the port that received the query is a dynamic router port in the router port list of the switch, the
switch restarts the aging timer for the port.
• If the port is not in the router port list, the switch adds it into the router port list as a dynamic router
port and starts an aging timer for the port.
MLD report
A host sends an MLD report to the MLD querier for the following purposes:
• Responds to queries if the host is an IPv6 multicast group member.
• Applies for an IPv6 multicast group membership.
After 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 one of the following actions:
• If no forwarding entry matches the group address, the switch creates a forwarding entry for the
group, adds the port that received the MLD report as a dynamic member port to the forwarding
entry for the group, and starts an aging timer for the port.
• If a forwarding entry matches the group address, but the port that received the MLD report 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 port that received the MLD report is in the
forwarding entry for the group, the switch restarts the aging timer for the port.
A switch does not forward an MLD report through a non-router port. The reason is that if the switch
forwards a report message through a member port, all the attached hosts that are listening to the
reported IPv6 multicast address, according to the MLD report suppression mechanism, suppress their