Overview of Multicast Listener Discovery

Multicast Listener Discovery (MLD) is the IPv6 equivalent of Internet Group Management Protocol version 2 (IGMPv2) defined in RFC 2236 for IPv4. MLD is a set of messages exchanged by routers and hosts, enabling routers to discover the set of multicast addresses for which there are listening hosts for each attached subnet. Like IGMPv2, MLD allows routers to discover the list of multicast addresses for which there is at least one listener on each subnet, and not the list of individual multicast listeners for each multicast address. MLD is described in RFC 2710.

A specification for IGMPv3 exists as an Internet draft ("Internet Group Management Protocol, Version 3") and is close to becoming an Internet standards track RFC, replacing IGMPv2. When this occurs, MLD for IPv6 will also be updated to include the features of IGMPv3 for IPv6 multicast hosts and routers.