As IPv4 address resources being exhausted, the transition from IPv4 to IPv6 is inevitable and fairly urgent. The existing IPv6 transition techniques encountered several critical issues for large-scale deployment. For example, the lack of unified evaluation criterion makes it hard to select the appropriate transition strategy for a given scenario. This paper investigates and presents potential IPv6 transition scenarios and typical transition mechanisms in ISP networks, with emphasis on the provision of unified evaluation criteria in terms of functionality, applications, performance, deployment and security for IPv6 transition mechanisms and evaluation of these transition techniques based on the provided criteria. In addition, by virtue of the unified evaluation criteria, this study proposes a practical deployment of IPv6 transition strategy in the ISP's core and access networks. Finally, the consideration of IPv6 transition based on the emerging technology such as SDN to ease and accelerate its deployment is presented.