跨越NAT的P2P应用UDP通讯

随着基于Internet的P2P网络技术的广泛应用，更多的内网主机需要参与到P2P中来。NAT之后的主机IP地址在Internet上是不可见的．Internet上的主机不能主动访问这些NAT之后的主机，但P2P网络要求任何主机之间都能够直接对等交换信息，这就使得P2P网络应用必须解决穿越NAT实现双向对等通讯的问题。本文在介绍了NAT基本原理和NAT对P2P应用的影响基础上，分析了客户端位于同一个NAT的后面、客户端位于不同的NAT的后面和客户瑞位于多级NAT的后面这三种情况下．P2P软件跨越NAT的UDP通讯问题。

UDP Communication Across NAT in Peer-to-Peer Applications

Following the widely application of P2P(Peer-to-Peer) network technology based on Internet, more and more computers behind the NAT(Network Address Translation) need joining P2P. IP addresses of these computers behind NAT is unseen from Internet, and computers in Internet can't access these computers behind NAT actively. But the P2P network requires that any computer can exchange information directly, thus P2P applications must solve the problem of bidirectional communication across NAT. The principle of NAT and the impact of NAT on P2P are discussed. The UDP communication across NAT in P2P applications under three situations is analyzed: peers behind a common NAT, peers behind different NAT and peers behind multiple levels of NAT.