Understanding FTP Ports: File Transfer & Port Numbers
Learn how ports are used with various file transfer protocols. The numbers, the connections, and a lot of communication between client and server.
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Video Transcript:
Hi, Karl with ExaVault here. Today we’re going to go over file transfers and port numbers. There are various protocols out there and successful file transfers can only happen when the correct ports are open.
In terms of FTP, ports are communication endpoints. Ports allow the connection and transfer of data to happen between a computer and a server.
In order to connect to a specific server, your FTP client needs to know that server’s IP address. While that IP address identifies a particular server, ports are numbers that are used to specify what application on the server you’re trying to communicate with. IP addresses are unique on the internet to one specific server that they are assigned to, but ports are more of a fixed range that goes from 0 to 65535.
When a service like FTP that accepts remote connection starts up, it starts listening on a specific port. For common services, there is an expected set port that the application should be using. The first 1024 ports are reserved for known special services. These services have been assigned a standard port by the Internet Assigned Numbers Authority or IANA.
When a file transfer client makes the connection to a port that a file transfer service is listening on, they can exchange information. Initially, this is in the form of commands. Commands establish the connection details and operations you want performed.
The next step involves transferring the file data requested. If using an active connection setting — this means while the client computer makes the connection request and sends commands, first on port 21, known as the control port, a connection to the server on port 20, AKA the data port is automatically opened to transfer your file data.
If using a passive SFTP connection, the client computer also connects on port 21, which is the FTP port. However, the server responds with a random port number in the free range of ports to use as the data port for file transfers. For example, your FTP client will open up a control channel on port 21 and a data channel on a random high port in the 60000-65535 port range.
Implicit FTPs uses different ports by default, starting with assigned FTPs port 990 to make the control connection. This initiates an SSL/TLS handshake. Then a connection to port 989 is made to transfer the encrypted file data.
SFTP uses a different port. The SFTP port is 22, the same as an SSH connection. In addition, it uses the same port for control messages and data transfers. The reason SFTP is implemented differently is that SFTP is not directly related to FTP. It is a secure file transfer protocol over SSH, modeled after the way that FTP operates.
With SFTP, both connection credentials and transfer data are always encrypted.
No matter what protocol you’re using, the ports open ensure that you are making the desired connection and that your data transfers efficiently between endpoints. Thanks for watching.
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