Mld Snooping - TP-Link T1700X-16TS User Manual

8.2 MLD Snooping

MLD Snooping
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Multicast Listener Discovery (MLD) snooping is applied for efficient distribution of IPv6 multicast
data to clients and routers in a Layer 2 network. With MLD snooping, IPv6 multicast data is
selectively forwarded to a list of ports that want to receive the data, instead of being flooded to all
ports in a VLAN. The list is constructed and maintained by snooping IPv6 multicast control packets.
MLD snooping performs a similar function in IPv6 as IGMP snooping in IPv4.
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. 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
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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 300 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
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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
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