1 install telnet. I don't have telnet under win7. Enter telnet under cmd, indicating that there is no such command. So we went to control panel-> programs-> to turn on or off windows functions. Then wait a while, check the telnet client and telnet server in the pop-up dialog box, don't worry about the others, and then click OK. The telnet component is now installed. \x0d\2。 Let's start testing whether a port is open. For example, I tested the port of 192. 168.3.42 at 212/kloc-0. Enter \ x0d \ start/min telnet192.168.3.422121\ x0d \ under cmd, and a window will appear, which will be minimized. Wait a minute. If the window closes automatically, the port is closed or the host cannot ping, otherwise. \x0d\3。 You can do experiments with your own computer. Enter netstat -anp tcp under CMD to see which ports are open in the current host tcp. \x0d\ Finally, the ping command cannot detect the port, but can only detect whether you can connect to the corresponding IP.