2. terminology
2. 术语
in this section we first summarize some middlebox terms. we focus hereon the two kinds of middleboxes that commonly cause problems for p2p applications.
在这一章节中，首先概要的介绍一下“代理”技术的一些术语。然后集中讨论两种造成p2p应用问题的代理机制。
firewall
a firewall restricts communication between a private internal network and the public internet, typically by dropping packets that are deemed unauthorized. a firewall examines but does not modify the ip address and tcp/udp port information in packets crossing the boundary.
防火墙
防火墙限制了私网与公网的通信，它主要是将（防火墙）认为未经授权的的包丢弃，防火墙只是检验包的数据，并不修改数据包中的ip地址和tcp/udp端口信息。
