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MLD Snooping Fundamentals
1. MLD Messages
MLD Queries：MLD Queries include General Queries and Multicast-Address-Specific Queries
(MASQs) and are sent out from the MLD router.
MLD Reports：When a host wants to join a multicast group or responds to the MLD queries, it will
send out an MLD report.
MLD Done Messages：When a host wants to leave a multicast group, it will send out an MLD
Done message to inform the IPv6 multicast routers of its leave.
2. Relevant Ports of the Switch
Router Port: Indicates the switch port that links toward the MLD router.
Member Port: Indicates the switch port that links toward the multicast members.
3. Timers
Router Port Aging Time: Within this time, if the switch does not receive MLD queries from the
router port, it will delete this port from the router port list. The default value is 260 seconds.
Member Port Aging Time: Within this time, if the switch does not receive MLD reports from the
member port, it will delete this port from the MLD multicast group. The default value is 260
seconds.
General Query Interval: The interval between the multicast router sends out general queries.
Last Listener Query Interval: The interval between the switch sends out MASQs.
Last Listener Query Count: The number of MASQs that the switch sends before aging out a
multicast address when there is no MLD report response.
MLD Snooping Process
1. General Query
The MLD router regularly sends MLD general queries to query if the multicast groups contain any
members. When receiving MLD general queries, the switch will forward them to all other ports in
the VLAN. The receiving port will be processed: if the receiving port is not a router port yet, it will
be added to the router port list with its router port aging time specified; if the receiving port is
already a router port, its router port aging time will be directly reset.
2. Membership Report
The host will send MLD report messages when it applies for joining a multicast group or responds
to the MLD query message from the router.
When receiving MLD report message, the switch will forward the report message via the router
port in the VLAN, and analyze the message to get the address of the multicast group the host
applies for joining. If the multicast group does not exist, it will create the group entry. The receiving
port will be processed: if the receiving port is a new member port, it will be added to the forward list
of the multicast group with its member port aging time specified; if the receiving port is already a
member port, its member port aging time will be directly reset.
3. Member Leave
The host will send MLD Done message when leaving a multicast group to inform the router of its
leaving.
When Immediate Leave is not enabled in a VLAN and a Done message is received on a port of
this VLAN, the switch will generate MASQs on this port to check if there are other members in this
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