Best answer
How to check if FTP port 21 is blocked or not
Before you start, first access the admin interface using the command line. In Windows, you open the console by pressing
Windows key + R. If using Mac or Linux, you use
F4 key for Mac or
Ctrl+Alt+T for Linux machine.
Then follow these steps to check if the FTP port is blocked:
Open the system console, and enter the following command. Make sure you have entered the correct domain name. This command can be used on any Operating System:
If port 21 is not blocked, a
220 response will be displayed. The message may be slightly different depending on the version:
If
220 does not appear, port 21 is blocked. If that is the problem, we recommend that you contact your ISP to open this port.
How to install Telnet
Since you are using the Telnet command, you need to make sure that the operating system you are using already has the Telnet Client.
Telnet is a client-server protocol for remote management of computers. In this case, it will help you to check whether the FTP Port is open or not.
Here is how to install Telnet Client on Windows machine:
Press Window+R, then type control to open the Control Panel.
Go to Programs -> Programs and Features. On the left sidebar, select Turn Windows features on or off.
Tick the Telnet Client box in the image above and then click OK.