font-size: 9pt; color: green; font-family: 宋体; mso-bidi-font-family: tahoma; mso-ascii-font-family: tahoma">建立连接时存储在nat b中的服务器s的地址信息不符。同样的，client b如果做同样的事情，发送的udp信息也会被 nat a 丢弃。
suppose a starts sending udp messages to b's public address, however, and simultaneously relays a request through server s to b, asking b to start sending udp messages to a's public address.? a's outgoing messages directed to b's public address (138.76.29.7:31000) cause nat a to open up a new communication session between a's private address and b's public address. at the same time, b's messages to a's public address (155.99.25.11:62000) cause nat b to open up a new communication session between b's private address and a's public address. once the new udp sessions have been opened up in each direction, client a and b can communicate with each other directly without further burden on the "introduction" server s.
