H3C Technologies H3C S12500-X Series Switches - Manual (Page 118)

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NOTE:
In MLD snooping, only dynamic ports age out. Static ports never age out.
How MLD snooping works
The ports in this section are dynamic ports. For information about how to configure and remove static
ports, see "
Configuring static ports ."
MLD messages include 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 identified by the address
FF02::1 on the local subnet to determine whether any active IPv6 multicast group members exist on the
subnet.
After receiving an MLD general query, the switch forwards the query to all ports in the VLAN except the
port that received the query. The switch also performs one of the following actions:
• If the receiving port is a dynamic router port in the router port list, the switch restarts the aging timer
for the router port.
• If the receiving port does not exist in the router port list, the switch adds the port to the router port
list, 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
IPv6 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 receiving port 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 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