Multicast Listener Discovery (MLD)

Multicast Listener Discovery (MLD) allows each IPv6 router to discover the presence of multicast listeners on its directly attached links, and to discover specifically which multicast addresses are of interest to those neighboring nodes.

MLD in IPv6 is similar to IGMP in IPv4.

MLD is needed to support IPv6 PIM and IPv6 multicast.

The role of MLD is to find out for which groups the routee is listening on each directly connected network.

In MLD, one router on each network is elected as the querier and sends MLD query packets, to which listeners respond. These responses tell all routers on the network what multicast groups may have listeners on the network. An MLD router implementation passes the information it gets to some multicast routing protocol such as IPv6 PIM.

For more infromation, see RFC 3810.