As the Internet grows, there are several problems needed be solve. First, the IP addresses will be exhausted. The 128 bits IPv6 addresses will replace the 32 bits IPv4 addresses to solve the problem. Secondly, routers become the bottlenecks of networks. There are many routing lookup algorithms to improve routers' performance. In July 1998, the detail address formats of IPv6 are defined by the IETF in RFC 2373, 2374 and 2375. These definitions make the discussion of routing lookup algorithms from IPv4 to IPv6 become possible. This paper focuses on the scalability of performing those IPv4 routing lookup algorithms for IPv6. The paper also proposals a new IPv6 lookup algorithm based on the characteristics of the IPv6 address formats. Chapter 1 is introduction. Chapter 2 introduces the current IPv6 addressing types and reviews previous work on IPv4. Chapter 3 presents our modified IPv6 routing lookup algorithm. Chapter 4 describes the generation of the test patterns for IPv6 lookups and presents the simulation results. Chapter 5 concludes this paper.