The port number of ftp is 21.
If you are using the linux os, just type the following command in the terminal,
telnet my-domain-name.com 21
If you are using the windows os,
1) click start>>run
2) In the text field, type cmd and press enter
3) A command line console opens and type the command
telnet my-domain-name.com 21
If you are using MAC os
1) Open the terminal (terminal is located in MAC HD>>Applications>>Utilities)
2) In terminal type the command
telnet my-domain-name.com 21
If the output of this command doesn't contains a welcome message, it indiacates that ftp is blocked.
