IPv4 over IPv6 multicast
The 4over6 mechanism is a mechanism to interconnect IPv4 networks over IPv6 backbones and provide IPv4-to-IPv6 transparent routing. The 4over6 unicast has been described in draft-wu-softwire-mesh-framework-00.txt. This memo provides the 4over6 multicast mechanism. We use BGP for discovering and maintaining the membership among all the Provider Edges (PE), and use IPv6 and IPv4 PIM-SM to construct the distribution tree. In the IPv6 backbone, static PIM-SSM trees are initially constructed for every PE. All the multicast traffic from the same PE are forwarded through only one PIM-SSM tree to avoid P routers maintaining too much state information. The process of encapsulation and decapsulation is the same as 4over6 unicast.