This document describes a mechanism to optimize the path between the
multicast router and multicast source in both IPv4 and IPv6 networks.
The basic idea is that when a multicast translation router has an
IPv4 path and an IPv6 path to the same multicast data source, and
both IPv4 and IPv6 joins are received, only one path is used. One
path is pruned, instead of the same traffic flowing over both v4 and
v6 paths. By adding a metric to the IPv4 path, the multicast
translation router can determine which path to receive multicast
data: IPv4 path, IPv6 path or both. Therefore, an optimization path
will typically be chosen when an identical v4/v6 traffic flow exists.