Nowadays, more and more attention is paid to the Mobile Ad hoc Network (MANET) because of its flexibility. To provide Internet access for MANET, the interworking mechanism between MANET and IP based fixed network is needed, which has become a vivid research area. However, so far, little work has been done to connect the multicast protocols on both sides so that users can access multicast services on either side. In this paper, a so-called Modified MLD (M.MLD) is proposed as a solution to IPv6 multicast interworking between MANET and fixed networks.