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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
multicast group. The user can control when a port membership is removed for an exiting address
in terms of the number and interval of MASQs. If there is no Report message received from this
port during the switch maximum response time, the port on which the MASQ was sent is deleted
from the multicast group. If the deleted port is the last member of the multicast group, the multicast
group is also deleted. The switch will send Done message to the router ports of the VLAN.
In IPv6，Layer 2 switches can use Multicast Listener Discovery (MLD) Snooping to limit the
flooding of multicast traffic by dynamically configuring Layer 2 interfaces so that IPv6 multicast
data is selectively forwarded to a list of ports that want to receive the data. This list is constructed
by snooping IPv6 multicast control packets.
The MLD Snooping function can be implemented on Global Config, VLAN Config, Filter Config,
Port Config, Static Multicast, Querier Config and Packet Statistics pages.
8.2.1 Global Config
To configure the MLD Snooping on the switch, please firstly configure MLD global configuration
and related parameters on this page.
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