File Transfer Protocol
From Halbeeg, the open encyclopedia · Af-Soomaali
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FTP (File Transfer Protocol) is a network protocol used to transfer files from one computer to another over a TCP/IP network. It is one of the oldest protocols in common use on the internet, and was created before the web existed.
The system operates on a client–server model. The client establishes a connection to the server and sends commands such as to list a directory, download a file, or upload a file. The server responds with a numeric code indicating whether the command succeeded or failed.
Two connections
A characteristic feature of FTP is that it uses two separate connections. The control connection, which handles commands, typically uses port 21 and remains open for the duration of the session. The data connection, which transfers files or listings, is created each time a file or listing is sent and then closed. This separation distinguishes FTP from many other protocols that handle everything over a single connection.
Active and passive modes
The data connection can be established in two ways. In active mode, the server initiates a connection to the client. In passive mode, the client initiates the connection and the server specifies the port it is listening on. Passive mode is generally preferred when the client is behind a firewall or NAT, since incoming connections from outside are blocked.
Security
Standard FTP transmits data and user credentials in plain text without encryption, making it vulnerable to network eavesdropping. For this reason, alternative solutions have been developed: FTPS, which wraps FTP in TLS encryption, and SFTP, which is an entirely different protocol that operates over SSH. Although the names are similar, SFTP and FTPS are not the same protocol.
Current use
FTP remains in use for web hosting, large file storage, and legacy systems. However, modern browsers have discontinued FTP support, and many organizations have migrated to HTTPS or SFTP for security reasons.