This memo specifies 6rd's multicast component so that IPv6 hosts can
receive multicast data from IPv6 servers. In the 6rd encapsulation
solution, multicast communication is completely integrated into the
6rd tunnel. In the 6rd translation solution, the protocol is based
on proxying MLD at the 6rd Customer Edge router interworking the MLD
messages to IGMP messages and sending them upstream through a network
which supports IPv4 multicast. The 6rd Border Relay is a multicast
router and interworks the IGMP to MLD for onward propasgation toward
the IPv6 multicast source. IPv6 Multicast data received at 6rd
Border Relay is translated into IPv4 multicast data and and delivered
through the IPv4 multicast tree downstream to the 6rd Customer Edge.
The latter translates it back to IPv6 multicast data then delivers it
to the hosts.