Unlike IGMPv2, MLD uses ICMPv6 messages instead of defining a separate message structure. Figure 7-1 shows the structure of an MLD message packet.
Figure 7-1. The structure of an MLD message packet
An MLD message packet consists of an IPv6 header, a Hop-by-Hop Options extension header, and the MLD message. The Hop-by-Hop Options extension header contains the IPv6 Router Alert Option described in RFC 2711. It is used to ensure that routers process MLD messages that are sent to multicast addresses for which the router is not a group member.