the reported IPv6 multicast group address to suppress their own reports. In this case, the switch cannot determine whether the reported IPv6 multicast group still has active members attached to that port.

Done message

When a host leaves an IPv6 multicast group, the host sends an MLD done message to the multicast router. When the switch receives an MLD done message on a member port, the switch first examines whether a forwarding entry matches the IPv6 group address in the message, and, if a match is found, determines whether the forwarding entry contains the dynamic member port.

•If no forwarding entry matches the IPv6 multicast group address, or if the forwarding entry does not contain the port, the switch directly discards the MLD done message.

•If a forwarding entry matches the IPv6 multicast group address and contains the port, the switch forwards the MLD done message to all router ports in the VLAN. Because the switch does not know whether any other hosts attached to the port are still listening to that IPv6 multicast group address, the switch does not immediately remove the port from the forwarding entry for that group. Instead, the switch resets the aging timer for that port.

After receiving the MLD done message, the MLD querier resolves the IPv6 multicast group address in the message and sends an MLD multicast-address-specific query to that IPv6 multicast group through the port that received the MLD done message. After receiving the MLD multicast-address-specific query, the switch forwards it through all its router ports in the VLAN and all member ports for that IPv6 multicast group. The switch also performs one of the following actions for the port that received the MLD done message:

•If the port (assuming that it is a dynamic member port) receives any MLD report in response to the MLD multicast-address-specific query before its aging timer expires, it means that some host attached to the port is receiving or expecting to receive IPv6 multicast data for that IPv6 multicast group. The switch resets the aging timer for the port.

•If the port receives no MLD report in response to the MLD multicast-address-specific query before its aging timer expires, it means that no hosts attached to the port are still monitoring that IPv6 multicast group address. The switch removes the port from the forwarding entry for the IPv6 multicast group when the aging timer expires.

Protocols and standards

RFC 4541, Considerations for Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Snooping Switches

Recommended configuration procedure

Step

Remarks

1. Enabling MLD snooping

Required.

globally

Disabled by default.

 

 

 

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