MLDv1 defines the IPv6 multicast member query and report mechanism. The process is the same mechanism as IGMPv2. The most significant difference between MLDv1 and MLDv2 is that MLDv2 allows hosts to specify the multicast sources from which they do or do not want to receive messages. The MLD versions are backward compatible. Therefore, a multicast router running MLDv2 can identify MLDv1 protocol messages.
Both MLD versions support the any-source multicast (ASM) model. MLDv2 can be directly used in the source-specific multicast (SSM) model; however, MLDv1 can be applied to the SSM model only when MLD SSM mapping is configured. For details about the ASM and SSM models, see Multicast Service Models.