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NOTE:
In MLD snooping, only dynamic ports age out. Static ports never age out.
How MLD snooping works
In this section, the involved ports are dynamic ports. For information about how to configure and remove
static ports, see "
."
A switch that runs MLD snooping performs different actions when it receives different MLD messages, as
follows:
When receiving a general query
The MLD querier periodically sends MLD general queries to all hosts and routers identified by the IPv6
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 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 receiving port is a dynamic router port in the router port list, restarts the aging timer for the
port.
•
If the receiving port is not in the router port list, adds it into the router port list as a dynamic router
port and starts an aging timer for the port.
When receiving a membership report
A host sends an MLD report to the MLD querier for the following purposes:
•
If the host has been a member of an IPv6 multicast group, responds to the query with an MLD report.
•
Applies for joining an IPv6 multicast group,.
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, 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, 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, restarts the aging timer for the port.
A switch does not forward an MLD report through a non-router port. If the switch forwards a report
message through a member port, the MLD report suppression mechanism causes all the attached hosts
that monitor the reported IPv6 multicast address suppress their own reports. This makes the switch unable
to know whether the reported multicast group still has active members attached to that port.
When receiving a 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
checks whether a forwarding entry matches the IPv6 multicast group address in the message, and, if a
match is found, whether the forwarding entry contains the dynamic member port.
