How do I check, if the port is open, using the ‘telnet’ command?

  1. press the Start button. In the Search field, type ‘cmd’ and press OK;
  2. in the opened window, type the command as follows:

    telnet server_name port_number
    telnet server_IP_address port_number

For instance, to check, if the operational port of SMTP is open, type the command:

telnet 25

If the command returns an error, this means the port is closed. If a server invitation appears (or the window goes completely empty), the port is open.

Telnet in Windows Vista and Windows 7

By default, in Windows Vista and Windows 7 the ‘telnet’ utility is disabled. You have to install it before using. The installation process is described on Microsoft website.