What is an File Transfer Protocol (FTP) Port?

Posted:  May 14th, 2018

 

The FTP, or the File Transfer Protocol, makes it possible for users to exchange files between their personal computers and remote servers with the help of specialized software tools called FTP clients. Through FTP software tools users can establish connections with a remote machine of their choice and perform any necessary data transfers. The FTP connections are executed through certain ports, which are either the default TCP ports or custom ports set by an administrator.

 

Executing an FTP port connection through a client is a two-stage process requiring the use of two different ports. Once the user enters the name of the server and the login credentials in the authorization fields of the FTP client, the FTP connection is established and the FTP control port of the FTP server (the default port for sending commands is 21) is opened. Then a second connection to the server is made by the client, followed by a response of the FTP server from the port for sending data (the default data sending port is 20), when the real file transfer actually begins.

 

Resolving problems with a blocked FTP port

 

As previously stated, the default command port for FTP connections is port 21, so, it's important to check if your ISP is not blocking the access to that port. To check if your router or ISP is blocking the port 21, you should use telnet. Depending on your OS, you can open a terminal (Linux, OSX) or a command prompt (Windows OS) and type the line below.

 

    An example of a telnet command to check FTP port 21:

If the connection is successfully opened, the result should be similar.

 

Results from the 21 port check:

 

If you didn't establish an FTP connection using telnet, you should check your firewall software and add your FTP Client in the exclusion / white list of programs which can open ports. If your FTP port is already listed there and you can't open an FTP connection using telnet, please contact your ISP and ask them to open port 21.

 

If you do connect to the FTP server using telnet, but you have problems in establishing an FTP connection using your FTP software, do the following:

 

    > check you FTP account details for errors

 

    > check the FTP client's connection settings

 

    > disable the simultaneous FTP transfers

 

    > set the number of the FTP connections to the minimum allowed

 

If all these tips don't allow you to connect to the server, try to set your FTP client in passive mode.