File Transfer Protocol (FTP) is a standard network protocol used for transferring files between a client and server on a computer network. Developed by Abhay Bhushan and introduced on April 16, 1971, FTP operates on the Application layer of the OSI model and utilizes separate control and data connections between the client and server. FTP allows users to authenticate themselves with a username and password, but it can also support anonymous connections if the server configuration permits it. For secure transmission that encrypts the username, password, and content, FTP can be secured with SSL/TLS (FTPS) or replaced with SSH File Transfer Protocol (SFTP), which encrypts both commands and data.
FTP works by establishing a connection between a client (the user’s computer) and a server (the remote host), typically requiring the client to log in with a username and password. However, some servers allow anonymous access. FTP operates in two modes: active and passive. In active mode, the server initiates a data connection back to the client after a command channel request. In passive mode, the server sends the client the information needed to open a data channel, making it more firewall and NAT-friendly.
Despite its long history and widespread use, FTP has several disadvantages, including the transmission of data, including usernames and passwords, in clear text, making it susceptible to eavesdropping. Additionally, FTP’s lack of encryption and vulnerability to various attacks, such as brute-force and spoofing, have led to the development of more secure alternatives like FTPS and SFTP.
FTP clients, software designed to facilitate file transfers using FTP, offer features like the ability to transfer multiple files and directories, resume interrupted transfers, and schedule transfers. Popular FTP clients include FileZilla, WinSCP, and Transmit. However, FTP clients also have drawbacks, such as the potential for data interception due to the transmission of data in clear text and difficulties in scripting and managing recursive changes.
In summary, FTP is a foundational technology for file transfer over networks, offering basic file transfer capabilities. Its simplicity and wide support have made it a longstanding choice for file transfers, though security concerns have led to the adoption of more secure protocols like FTPS and SFTP for sensitive data transfers.