Mld Snooping; Mac Address Control Method - Alaxala AX2200S Series Configuration Manual

24 Description of IGMP Snooping and MLD Snooping

24.4 MLD Snooping

The following explains MLD snooping functionality and its operation. The format and
established values for MLD messages sent and received by the Switch conform to RFC
2710. Also, the format and set values for MLD version 2 (abbreviated hereafter to MLDv2)
messages conform to RFC 3810.
When MLD snooping is used, the MAC address control method is used to control
forwarding for multicast traffic.

24.4.1 MAC address control method

(1) MAC address learning
For VLANs for which MLD snooping is set, multicast MAC addresses are dynamically
learned when MLD messages are received. The learned multicast MAC addresses are
registered to the MAC address table.
(a) Registering entries
When an MLDv1 Report message or MLDv2 Report (membership request) message is
received, the multicast MAC address is learned from the multicast group address included
in the message, and an entry is created that forwards traffic bound for a multicast group
only to ports for which MLDv1 or MLDv2 Report messages have been received.
Destination MAC addresses for IPv6 multicast data are generated by copying the lowest 32
bits of the IP address to the MAC address.
IPv6 multicast addresses have two types of formats for group ID fields that identify
multicast groups: a 112-bit format and a 32-bit format. When group ID fields use the 112-bit
address format, duplicate MAC addresses occur the same as for IPv4 multicast addresses.
The following figure shows the correspondence between IPv6 multicast addresses and
MAC addresses.
Figure 24-4 Correspondence between IPv6 multicast addresses and MAC addresses
(b) Deleting entries
Learned multicast MAC addresses are deleted in any of the following cases when group
members no longer exist on all ports:

An MLDv1 Done message is received.
Group-Specific Query messages are sent from the Switch to the port that received
MLDv1 Done messages, twice every second (Group-Specific Query messages are
only sent when a querier is set and are sent from a representative querier otherwise).
If there is no response, only that port is deleted from the entries (forwarding of
multicast traffic to this port is suppressed). If no group members are left in all ports in
the VLAN, the entry itself is deleted.

An MLDv2 Report (detachment request) message is received.
Group-Specific Query messages are sent from the Switch to the port that received
MLDv2 Report (detachment request) messages, twice every second (Group-Specific
Query messages are only sent when a querier is set and are sent from a
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