31.2.1 Introduction to MLD

MLD is a IPv6 multicast group management protocol used between routers and hosts. It has the same functionality as IPv4 multicast IGMP.

Using the MLD protocol, the router asks hosts whether they have joined IPv6 multicast groups, and the hosts reply to the router. In this way, the router recognizes whether hosts have joined or left IPv6 multicast groups in order to control whether to forward or block IPv6 multicast packets. The MLD protocol functionality is the same as the IGMP functionality, except that the MLD protocol uses IPv6 addresses for communication.

Two versions of MLD (MLDv1 and MLDv2) have been described in RFCs.

MLDv2 is a protocol extended from MLDv1 to implement IPv6 multicast group management functionality by introducing functionality to filter senders so that multicast packets are only received from specified senders. Because senders can be specified when the joining or leaving of an IPv6 multicast group is reported, MLDv2 and PIM-SSM can be used in combination to implement more efficient IPv6 multicast forwarding.

The format and setting values for MLDv1 messages sent by the Switch follows RFC 2710. Likewise, the format and setting values for MLDv2 messages follow RFC 3810.