refer to [nat-trad] and [nat-term] for more general information on nat taxonomy and terminology. additional terms that further classify napt are defined in more recent work [stun]. when an internal host opens an outgoing tcp or udp session through a network address/port translator, the napt assigns the session a public ip address and port number so that subsequent response packets from the external endpoint can be received by the napt, translated, and forwarded to the internal host. the effect is that the napt establishes a port binding between (private ip address, private port number) and (public ip address, public port number).
the port binding defines the address translation the napt will perform for the duration of the session. an issue of relevance to p2p applications is how the nat behaves when an internal host initiates multiple simultaneous sessions from a single (private ip, private port) pair to multiple distinct endpoints on the external network.
网络地址和端口转换 （napt）
这是最普遍的情况，网络地址/端口转换器检查、修改包的ip地址和tcp/udp端口信息，这样，更多的内部主机就可以同时使用一个公网ip地址。
