Written by Christian Ahmer | 11/18/2023

FTP (File transfer protocol)

File Transfer Protocol (FTP) is a standard network protocol used for the transfer of computer files between a client and server on a computer network. FTP is built on a client-server model architecture using separate control and data connections between the client and the server. It is one of the oldest protocols used on the Internet and is designed to allow for easy and reliable transfer of files.

How FTP Works

FTP works on a client-server model where the client initiates a connection to the server to request files. There are two channels of communication in an FTP session:

  • Control Channel: This is used for sending control information like user identification, password, commands to change directory, and commands to put or get files.
  • Data Channel: This is used for the actual transfer of files.

Users typically interact with FTP through a client, a software application designed to send and receive files from an FTP server. Some web browsers also have FTP functionality built-in, allowing users to access files on FTP servers via a simple interface.

FTP Commands

FTP clients use a series of text-based commands to interact with the server. Some common commands include:

  • USER: Send username.
  • PASS: Send password.
  • LIST: List files in the current directory.
  • CWD: Change working directory.
  • PASV: Enter passive mode.
  • RETR: Retrieve a file from the server.
  • STOR: Store a file on the server.

Modes of FTP

FTP can operate in either active or passive mode, which determines how the connection between a client and server is established.

  • Active Mode: The client opens a port and listens while the server actively connects to it.
  • Passive Mode: The server opens a port and listens (passively) while the client connects to it. This mode is often necessary when clients are behind a firewall.

Security

Traditional FTP does not encrypt its traffic, and all transmissions are in clear text, including usernames, passwords, commands, and the data itself. This can present a security risk, especially when used over unsecured networks like the Internet. To overcome this limitation, variations like FTP Secure (FTPS) and Secure Shell (SSH) File Transfer Protocol (SFTP) have been developed.

  • FTPS: Also known as FTP Secure or FTP-SSL, FTPS adds support for the Transport Layer Security (TLS) and the Secure Sockets Layer (SSL) cryptographic protocols.
  • SFTP: Part of the SSH Protocol Suite, SFTP (SSH File Transfer Protocol) provides secure file transfer capability but is not interoperable with FTPS.

Usage

FTP is widely used for uploading files to a server (such as a website's content to its hosting server), downloading files to a client (such as when downloading software from a public server), and transferring files between systems for data exchange.

FTP Clients

There are numerous FTP clients available that offer a graphical user interface (GUI) to make file transfers more user-friendly. Popular clients include FileZilla, WinSCP, and Cyberduck. These clients often support FTP along with FTPS and SFTP.

Conclusion

Despite being one of the older protocols, FTP remains in use due to its simplicity and wide support across different computing systems. While security concerns have led to the development of more secure variations of FTP, the basic functionality remains valuable for the basic task of transferring files, especially in internal or trusted network environments. For secure file transfers over the internet, however, FTPS or SFTP are recommended over standard FTP.