What Is Port 20 For Computers? | GigMocha Defines

The physical ports in your computer are your ways of communicating with peripheral devices like your mouse and keyboard, and they also enable you to connect to the internet. In computer networking, the ports work in a similar way, i.e. they are used when you want to connect two computers in some way. One of the most commonly used is port 20, but what exactly is it and how is it used? 

Port 20 is one of the main ports in computer networking, and it serves to transfer data via the Data Channel. Port 20 uses the Transmission Control Protocol (TCP) that is concerned with connections between two computers. Through port 20 you can receive data in the same order in which they were sent. 

Below, I have explained what port 20 means for computers and in what way it is used. I also discussed which protocols this port uses and how data is communicated over different networks. If this is your first time reading about port 20, you will be surprised how many times you have used it without even knowing. 

What Is Port 20? 

Port 20 is one of the most used ports in computer networking since it serves to transfer data from one computer to another. When it comes to transferring data, we refer to the File Transfer Protocol (FTP) which is one of the main protocols in computer networking. FTP and port 20 usually go together, since everything that we do on our computers is often shared and transferred elsewhere. 

File transfer is one of the most used TCP/IP applications and it is responsible for sharing data between computers through a network. Before the internet became available to everyone, there were various standard transfer protocols that people used as software for transferring data. These protocols helped in the creation of the File transfer protocol, which we nowadays refer to as FTP. 

FTP uses TCP as a protocol for transfer. TCP stands for Transmission Control Protocol and it is characterized by robustness and reliability for transferring files. When FTP uses TCP as the main protocol, it means that FTP inherits the characteristics of TCP and becomes really reliable in the case of transferring files and other data. 

It is a fact that many people use FTP without even realizing it. If you have downloaded files on your computer, that means you have used FTP, and along with it, you have used port 20. Port 20 is responsible for files coming your way properly. 

In other words, in order to have files transferred from one computer to another through a network, you use three components – FTP, TCP, and port 20. FTP uses TCP as a transport, and port 20 for transferring the files via the data channel. FTP also uses port 21, but in that case, it does not transfer files but establishes the connection between two computers. 

There are cases in which port 21 can be used for both, establishing a connection and transferring files. However, that is not possible for port 20 since it is only responsible for data transfer. 

Since we established what is port 20 and what is FTP, now it is time to make the differences of FTP in its two modes. It is important to remember that FTP uses active and passive modes for operation. You can only use one, and that usually depends on whether your computer uses a firewall or not. 

FTP Active Mode

When your computer does not use a firewall, that means that you use the active mode of FTP. In this case, you have a direct connection to the internet, and once you try to establish a connection to the FTP server, your second port number uses the Data Channel. This is used for the exchange of files. 

Once the connection is established, the FTP server starts the transfer from port 20 to any kind of port created by your workstation. Since the server initiated the data exchange, that means that the client has no control over it. However, in this situation, the server can allow uninvited data to enter your computer and harm it in some way. 

Therefore, the active mode of FTP is not recommended much, and many networking experts suggest using the passive mode only for transferring files. 

FTP Passive Mode

The passive mode is also referred to as the normal mode of FTP in which the exchange of files begins once the client sends a request for communication through TCP. However, in this case, the TCP does not use port 20, but port 21. This is the situation in which port 21 can be used both for establishing connections and exchanging data.

Port 21 is the only possible port for the passive mode of FTP. This communication is referred to as Control Channel connection. In this case, it is not the port that sends the command, but PASV. 

Unlike the active mode, this mode allows the PASV command to ask the server to which port the data should be transferred. The server sends a message to the Data Channel with the client’s port number and then starts the transfer. This is the reason why the passive mode is way more secure than the active mode of FTP. 

You can always set your FTP program to use the Active or the Passive mode. You just have to head over to FTP Settings, and in Options, you should select the Firewall tab. Just like that, you will enable the passive mode of FTP. 

You can always go back to active mode by removing the options you previously selected. However, if your computer is behind a firewall, the active mode would never be an option. 

As you could see, port 20 is one of the most used ports in computer networking for exchanging data. It is the connection created in an FTP session, and it enables files to be transferred from one computer to another. Port 20 can be also referred to as Data Channel since the exchange happens through it.