端口扫描能够用来查找目标主机已开放的端口，包括TCP和UDP端口。当前针对TCP端口的扫描技术有三种，分别为：全连接扫描，SYN扫描和FIN扫描。针对UDP端口的扫描技术一般是采用ICMP报文中端口不可达的信息来识别UDP端口是否开放。(Port scans can be used to find ports that have been opened by the target host, including TCP and UDP ports. There are three kinds of scanning technology for TCP port, which are full connection, SYN scan and FIN scan. The scanning technology for UDP ports generally uses the inaccessible information of the port in the ICMP message to identify whether the UDP port is open.)