Port 21 is a default TCP port for each FTP connection. When this port is blocked by ISP, this causes for FTP connection issues.
Following are processes in Windows and Linux OS to check ISP port 21 is blocked or not.
- port 21 checkout in Windows.
Go to Start Button >> Run or press Windows + R
This will open Run window on the screen. Type ‘cmd’ command and press the ‘Enter’ key.
You will come to ‘command prompt window which is of ‘MS-DOS’ type.
Type the following command in it (without quotes)
‘telnet my-domain-name.com 21’
- port 21 checkout in Linux.
This is simple and short method to check the port 21 check in Linux operating system. In terminal emulator you need to to execute ‘telnet my-domain-name.com 21′ command.
If you received following output after running the above command in both Operating systems, then the test can be considered successful.
220———- Welcome to Pure-FTPd [TLS] ———-
220-You are user number 2 of 50 allowed.
220-<<
220-#########################################################
220-Please upload your web files to the public_html directory.
220-Note that letters are case sensitive.
220-#########################################################
220->>
220-Local time is now 03:35. Server port: 21.
220-This is a private system – No anonymous login
220-IPv6 connections are also welcome on this server.
220 You will be disconnected after 15 minutes of inactivity.
And if you are unable to see the above output then you should unblock port 21 by requesting your ISP provider.