Telnet protocol allows you to test if a port is open to connections or not using simple telnet command. To run the command, you need to have the telnet client installed.
Steps to enable Telnet client on a Windows PC:
- Visit the control panel, and click on 'Programs'
- Select 'Turn Windows features on or off'
- From the windows feature window, scroll down to 'Telnet Client'
- Enable the client by clicking on the checkbox if it is blank
For a Linux system, you can directly execute the telnet command in the terminal without any installation.
Telnet command syntax
- telnet <space> <Domain name or IP> <space> <port>
- eg:
- telnet 192.12.1.38 25
- telnet {domain}.mithiskyconnect.com 1125
Expected Output
- If the connection succeeds, there will be no output shown and a blank screen with a blinking cursor will pop up. This indicates that the port is open.
- Sometimes, an open port will also display a series of messages such as: trying <IP>, connected <domain> and escape character. This also means that the connection is successful for the port.
- Any other output messages, such as connection failed, operation timeout, access denied and more, indicate that the port is closed.