China Telecom China Telecom China Telecom 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.