Desgin And Study Of IPv4/IPv6 Translation Gateway System

With the Internet technology innovating and rapid growth of the number of users, IPv4 address resources have exhausted. The next generation network protocol-IPv6 Protocol provides a huge address space, more security, better supporting for streaming media, Mobile Internet and other new technologies, therefore, large-scale deployment of IPv6 networks is imperative. However, the Internet can not to change from IPv4 to IPv6 in the short period of time, and it is a gradual process. Interactive visits between the IPv4/IPv6 network is an important issue in IPv4 to IPv6 transition program.The paper studies a key technology during the transition period-the IPv4/IPv6 translation gateway. The IPv4 clients visiting the IPv6 network is always a big technology challenge. This system is based on NAT-PT technology, combined with DNS-ALG module to achieve TCP/UDP protocol transparent transmission, IPv4/IPv6 network two-way communication (bi-directional NAT) and increases the reused number of one IPv4 addresses (bi-directional NAPT).The paper introduces the background and significance of the subject; it studies the characteristics of IPv6 protocols and the relevant theory of network protocols which is the key knowledge points in the construction of the gateway system, such as IPv6 and IPv4 header format, ICMPv4 and ICMPv6 protocols, TCP/UDP protocols; it deeply studies NAT-PT, including network address translation technology (NAT) which is divided into traditional NAT, bi-directional NAT, bi-directional NAPT, and protocol translation technology (PT) whitch is divided into IPv4/IPv6 protocol translation, ICMPv4/ICMPv6 protocol translation; it designs the structural of the system, the entire system is divided into the system scheduling module, the IPv4/IPv6 address translation module, the IPv4/IPv6 protocol translation module, the application layer gateway modules. It analyzes each module of the design principles and algorithms.The data structure of NAT address mapping list combines Hash table and two-way liner list which improves the efficiency of addresses'lookup and translation.It described in detail the DNG-ALG work process of IPv4 or IPv6 side initiating the communication and the interaction bewteen DNS-ALG and IPv4/IPv6 address translation module, it designs on the FTP-ALG and SIP-ALG module; Through the implementation of each module fuction completes IPv4/IPv6 bi-directional communication, it highlights the function implementation of IPv4/IPv6 NAT module, the function implementation of IPv4/IPv6 PT module and the function implementation of DNS-ALG module; Finally, the gateway system's function is verified by the tests and the result show that it basicly realized the objectives and requirements.