Although the basic protocol of the Next-Generation Internet (NGI) was defined as IPv6 over 10 years ago, the transition from the current IPv4-based Internet to IPv6-based NGI was still a long way to go. With the growth of Internet, it is predicted that IANA will exhaust its IPv4 address pool on 17-Jun-2011. Therefore, IPv6 networks and IPv6 applications will be widely used in the coming days. However, as different address families, IPv4 and IPv6 are difficult to inter-connect or even long-term coexist in the complex topology of Internet. After giving some basic IPv6 transition technologies in the literature, the talk will present the active work in IETF for IPv4/IPv6 coexistence. At last, the IPv6 progress in China will also be introduced.