The IANA free pool of IPv4 addresses was depleted, IPv6 migration has
become the most imperative task. There are many transition
mechanisms designed for different scenarios, however, some problems
arosed in the practice. FAST6, specified in this draft, is based on
the ideas of native dual stack and address sharing. It can solves
the mixed route problem and simplify the planning of private IPv4
address space by using tunnel technology. FAST6 is an economical and
stable technology for smooth network transition.