TP-Link T2500-28TC User Manual page 170

The switch, running MLD Snooping, listens to the MLD messages transmitted between the host
and the router, and tracks the MLD messages and the registered port. When receiving MLD report
message, the switch adds the port to the multicast address table; when the switch listens to MLD
Done message from the host, the router sends the Multicast-Address-Specific Query message of
the port to check if other hosts need this multicast, if yes, the switch will receive MLD report
message; if no, the switch will receive no response from the hosts and the switch will remove the
port from the multicast address table. The router regularly sends MLD query messages. After
receiving the MLD query messages, the switch will remove the port from the multicast address
table if the switch receives no MLD report message from the host within a period of time.
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
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