File Transfer Protocol

Passive FTP Verbindung

FTP model

1st-ftp-southpole-1994

FileZilla

Primitive FTPd screenshot

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 and uses separate control and data connections between the client and the server. FTP users may authenticate themselves with a sign-in protocol, normally in the form of a username and password, but can connect anonymously if the server is configured to allow it.

Overview

FTP was originally defined in 1971, prior to the establishment of the Internet Protocol Suite, with updates in 1980, 1985, and 1997. It operates on the application layer of the OSI model and is used to transfer files using TCP/IP protocols. FTP is a reliable, connection-oriented service that uses TCP to ensure the reliable delivery of files. It is traditionally used in applications where a user needs to transfer large files or a large number of files over a network.

Operation

The operation of FTP is based on a client-server model. The FTP server runs an FTP daemon that is constantly listening for FTP requests from remote clients. When a client wants to make an FTP connection, it initiates a connection to the server. Once the connection is established, the client can perform various operations such as uploading, downloading, renaming, or deleting files on the server.

FTP operates using two channels: a command (or control) channel and a data channel. The command channel is used for sending commands between the client and server (such as login or directory listing requests), while the data channel is used for the actual transfer of files.

Modes

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

• In active mode, the client opens a port and listens, and the server actively connects to it.
• In passive mode, the server opens a port and listens (making it firewall-friendly), and the client connects to it.

Security

Since its inception, FTP has been known to have several security weaknesses. The primary concern is that data, including usernames and passwords, are transferred in plain text, making it susceptible to eavesdropping and man-in-the-middle attacks. To address these concerns, versions of FTP secure through SSL/TLS (FTPS) or SSH (SFTP) have been developed to provide encryption.

FTP Clients and Servers

There are numerous FTP clients and servers available, ranging from command-line utilities to graphical user interface (GUI) applications. Popular FTP clients include FileZilla, WinSCP, and Cyberduck, while common FTP server software includes vsftpd, ProFTPD, and FileZilla Server.

Usage

Despite the rise of more secure alternatives, FTP remains widely used in the corporate and academic worlds for file sharing, website management, and in the transfer of large data sets in scientific research.

See Also

• File Transfer Protocol Secure (FTPS)
• SSH File Transfer Protocol (SFTP)
• Trivial File Transfer Protocol (TFTP)
• Hypertext Transfer Protocol (HTTP)

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