Multicast Listener Discovery (MLD) is a protocol used by an IPv6 router to discover the presence of multicast listeners (that is, nodes wishing to receive multicast packets) on its directly attached links, and to discover specifically which multicast addresses are of interest to those neighboring nodes.
MLD snooping restricts IPv6 multicast traffic by forwarding multicast packets only to the interested recipients. It is a Layer 2 feature which restricts IPv6 multicast traffic within a VLAN to a subset of ports that have transmitted or received MLD queries or reports. The benefit of using MLD snooping is that you can conserve the bandwidth on those segments of the network where no node has expressed interest in receiving the multicast traffic.
MLD is derived from IGMP; MLD Version 1 (MLDv1) is equivalent to IGMPv2, and MLD Version 2 (MLDv2) is equivalent to IGMPv3. MLD is a subprotocol of Internet Control Message Protocol Version 6 (ICMPv6), and MLD messages are a subset of ICMPv6 messages, identified in IPv6 packets by a preceding Next Header value of 58.
The router supports two versions of MLD snooping:
MLDv1 snooping detects MLDv1 control packets and sets up traffic bridging based on IPv6 destination multicast addresses.
MLDv2 basic snooping (MBSS) uses MLDv2 control packets to set up traffic forwarding based on IPv6 destination multicast addresses.
The router can snoop on both MLDv1 and MLDv2 protocol packets and bridge IPv6 multicast data based on destination IPv6 multicast addresses.