Research On NAT Traversal Method Based On LINUX System

With the rapid development of Internet, especial the emergence of P2P technology, a growing number of users connect to the network, to make use of the technology to exchange, to transfer files, to progress distributed computing. The application of P2P technology needs legal IP addresses, however, the shortage of IP addresses seriously limites a wide range of applications of the P2P technology in the existing network environment. In order to solve the problem, network address translation(NAT) technology is proposed. It is better to solve the problem of the shortage of public network IP address, and to ensure the network security, while NAT also affected the direct communications of peer-to-peer network. At the same time, widespread adoption of NAT circumstances, advantages of symmetric NAT such as security features and so on, are accepted by a large number of enterprises. Although, it is based on the popular STUN for UDP traversing the NAT to make a very excellent solution, it is not to traverse symmetric NAT.In order to traverse symmetric NAT, the dissertation is based on the NAT function, principle, and the basic principle of the existing program traversing the NAT to do further analysis, by comparing the research to identify the existing deficiencies,and combining with the way of P2P NAT through port prediction.The method is based on the prediction, and use the building and sending engine of Linux kernel libnet packet as well as the capturing engine of libpcap packet.The dissertation proposes the prediction algorithm based on the NAT port mapping structure. It is not only to compile the traversing algorithm of the client end and the server end, but also to expound the implementation process of the NAT traversing algorithm and to verify its feasibility furtherly. Finally, we use virtual machine to set up NAT traversal environment, it is impleted the algorithm P_P2PNAT applications, to set up TCP connection at both the client. Results of Experimental show the feasibility of the algorithm, and achieve the success of traversing the symmetric NAT.