NAT技术探讨及应用实例

THE STUDY AND REALIZATION OF NAT TECHNOLOGY

对 NAT(网络地址转换 )技术进行了深入的分析 ,探讨了其应用的范围。通过实现NAT技术的 C程序源代码 ,介绍了 NAT技术的原理和实现方法。同时 ,也讨论了 NAT技术的不足之处和其可能带来的不安全之处 ,指出其不能适用的范围。针对由于 IP地址分配的局限性 ,探讨了同一个 IP地址段的 IP地址如何进行转发的问题 。

The Internet has grown larger than anyone ever imagined it could be. In fact, the rate of growth has been such that the Internet is effectively doubling in size each year. For a computer, to communicate with other computers and Web servers on the Internet, it must have an IP address. An IP address (IP stands for Internet Protocol) is a unique 32 bit number that identifies the location of your computer on a network. Basically it works just like your street address: a way to find out exactly where you are and deliver information to you. This is where NAT comes to the rescue. NAT technology is the simplest of all Internet connection techniques. NAT translates all the IP addresses used on an internal network into different return IP addresses for the Internet. It rewrites the addresses in the header of each outgoing (network to Internet) packet to reflect a new address and keep tracks of this change, so it may route incoming packets to the correct machine. To maintain data integrity, every packet has a checking process that results in an error message if any portion of the package has been corrupted or modified. NAT advantages include its quick and easy installation, with no application adjustments required on client PCs. Basically, Network Address Translation allows a single device, such as a router, to act as an agent between the Internet (or 'public network') and a local (or 'private') network. This means that only a single unique IP address is required to represent an entire group of computers to anything outside their network . The shortage of an IP address is only one reason to use NAT. Two other good reasons are Security and Administration. The occupancy of IP address resources will be reduced by employing NAT technology. The user of LAN can freely access Internet. The user outside LAN can get resources on the Internet. NAT technology can ensure the safety of NAT system, while reducing the limitation of distribution of ISP address. At the same time, the shortage and insecurity of NAT technology is studied. The area of NAT application is talked about too. For the IP address which is in a same subnet cannot be translated, the way how to resolve the issue is given .