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File Transfer Protocol

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The File Transfer Protocol, commonly known as FTP, is a standard communication protocol. It is used to transfer computer files between a client and a server on a network.

FTP model
FTP model

This system relies on a client-server model architecture. In this setup, the client is the computer requesting files. The server is the computer that stores and provides those files. FTP is a fundamental tool for moving data across different computer systems.

FTP operates using two separate connections to manage tasks efficiently. One connection is for control, which carries commands from the user. The second connection is for data, which carries the actual files being moved.

Passive FTP Verbindung
Passive FTP Verbindung

This dual-connection method traces back to the Network Control Protocol (NCP). NCP was a simplex protocol that used two separate port addresses for two-way communication. Even after the standardization of TCP and UDP, FTP kept this two-port design for backwards compatibility.

There are two primary ways to establish the data connection: active mode and passive mode. In active mode, the client tells the server which port it is listening on using a PORT command. The server then initiates the data connection from its own port 20. However, firewalls often block these incoming connections. To solve this, clients use passive mode. In this mode, the client sends a PASV command to the server. The server responds with an IP address and port number. The client then opens the connection to the server, which allows the data to pass through firewalls.

FTP model
FTP model

FTP can handle many different types of data through various modes. ASCII (TYPE A) is used for plain text files. It converts characters to ensure they are readable on different systems. For files like images, computers use Image mode, also called Binary mode (TYPE I). In this mode, the machine sends the file byte by byte. This ensures the file remains exactly the same when it arrives. Other specialized types include EBCDIC (TYPE E) for specific character sets and Local mode (TYPE L), which supports machines that do not use 8-bit bytes.

Google Chrome - FTP is Not secure
Google Chrome - FTP is Not secure

The history of FTP began with Abhay Bhushan. He wrote the original specification and published it on April 16, 1971.

1st-ftp-southpole-1994
1st-ftp-southpole-1994

Originally, FTP ran on the NCP protocol. By June 1980, it was updated to run on the TCP/IP protocol. Another major update occurred in October 1985 to refine the current specification. Over the years, several standards were proposed to improve the system. These included updates for IPv6 in 1998 and new ways to make the protocol more firewall-friendly.

Security is a major consideration when using FTP. Standard FTP uses a plain-text sign-in protocol. Users provide a username via the USER command and a password via the PASS command. Because this information is unencrypted, it can be vulnerable to network sniffing attacks.

Google Chrome - FTP is Not secure
Google Chrome - FTP is Not secure

To protect sensitive data, users often use FTPS, which uses SSL/TLS encryption. Another secure alternative is the SSH File Transfer Protocol, or SFTP. Because of these security risks, major web browsers like Google Chrome and Firefox dropped support for the standard FTP protocol in 2021.

Today, FTP is integrated into many different types of software. Many file managers, such as Windows File Explorer, include FTP access. On Linux systems, the KDE file managers Dolphin and Konqueror support both FTP and SFTP.

Primitive FTPd screenshot
Primitive FTPd screenshot

Some servers even allow anonymous FTP. This allows users to log in without a personal account, often using the username "anonymous." This is frequently used by hosts that provide public software updates. While newer, more secure protocols are becoming the standard, the core concepts of FTP remain vital to network communication.

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File:Google Chrome - FTP is Not secure.png
Google Chrome - FTP is Not secure.png
File:Passive FTP Verbindung.svg
Passive FTP Verbindung.svg
File:FTP model.png
FTP model.png
File:1st-ftp-southpole-1994.jpg
1st-ftp-southpole-1994.jpg
File:Primitive FTPd screenshot.png
Primitive FTPd screenshot.png
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