The default TCP port for FTP connection is port 21. Manytimes the local Internet Service Provider blocks this port and this will effect in FTP connection issues.
Here’s how to, depending on your OS, check whether your ISP blocks port 21:
Check port 21 with a Windows OS
Click on the Start menu button, Normally place on the left low corner of the screen. There is a tab known as “Run”. You have to click on it, in order to continue further. You will find the appearance of a new small window on the screen. In the text field of this window you require to type “cmd” and then press the “Enter” key. Other window will open. It is the so called “MS-DOS prompt” or “command prompt”. Just type the following command in the command prompt window and press “Enter”:
telnet my-domain-name.com 21
Check port 21 with Apple/Mac
Every Mac OS delivered with a preinstalled terminal emulator. The terminal is a tool which permit you to carry out commands from the command line. Normally, the terminal is located under your Mac HD -> “Applications” directory -> Utilities sub-directory. When the window opens, you will see a command line with a flashing cursor on it so you can start typing right away. Just type the following command and press “Enter”:
telnet my-domain-name.com 21
Check port 21 with Linux
Open your selected terminal emulator and run the following command in order to telnet your website:
telnet my-domain-name.com 21
Results from the 21 port check
If the test is successful, you should receive a message. The message is given below.
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 disconnected after 15 minutes of inactivity.
If you don’t find above welcome message, then you can contact your local ISP and ask them to unblock this port for you.