File Transfer Protocol (FTP) is a standard network protocol that is used for transferring files between a client and a server over a computer network. It was developed in the 1970s as a standard for transferring files over the ARPANET, a precursor to today's Internet.

It operates over the Transmission Control Protocol (TCP), typically using port 21 for command control and port 20 for data transfer.

FTP operates using a client-server model. The client initiates a connection to an FTP server. Once connected, the client can do a variety of file operations like uploading, downloading, renaming, deleting, and more. FTP uses two channels between client and server: command (or control) channel and data channel. The command channel is for sending commands and receiving responses, while the data channel is for transferring the actual files.

FTP can operate in two modes:

  • Active Mode: The client listens for incoming data connections from the server. It's less common nowadays due to issues with firewalls and Network Address Translation (NAT).
  • Passive Mode: The server listens for incoming data connections from the client. It's more firewall and NAT-friendly.

FTP is a CLI-based utility, and as such has a series of text commands to control file and directory operations. Some common ones include: - GET: Download a file from the server. - PUT: Upload a file to the server. - LIST: List files in the current directory on the server. - CD: Change directory on the server.

FTP, in its basic form, is not secure. Usernames, passwords, and even the data itself are transmitted in clear text, which means they can be intercepted and read. This vulnerability led to the development of FTPS (FTP Secure). FTPS is FTP with SSL/TLS encryption.

Another secure alternative to FTP is SFTP (Secure File Transfer Protocol), which is different from FTP and operates over SSH (Secure Shell), offering both command and data connection encryption.

While FTP and FTPS are still in use today, many organizations and users have shifted towards more secure and versatile methods like SFTP or SCP (Secure Copy Protocol) due to the security concerns with classic FTP. However, FTP is still often used in website maintenance, backup, and data transfer tasks, especially in environments where its vulnerabilities are not a primary concern.

There are many FTP clients and servers available, ranging from command-line tools to graphical user interfaces. Some popular FTP clients include FileZilla, WinSCP, and Cyberduck.

FTP is a foundational protocol in the history of the internet for file transfer. However, its security shortcomings have led to the development and adoption of more secure alternatives in modern computing environments. If you're planning to use FTP, it's recommended to opt for secure versions like FTPS or SFTP.