The primary general file transfer protocol in the TCP/IP suite shows its “generality” directly through its unqualified name: the File Transfer Protocol (FTP). FTP is one of the most widely used application protocols in the world. It was designed to allow the efficient transfer of files between any two devices on a TCP/IP internetwork. It automatically takes care of the details of how files are moved, provides a rich command syntax to allow various supporting file operations to be performed (such as navigating the directory structure and deleting files) and operates using the TCP transport service for reliability.

In this section I describe the operation of the File Transfer Protocol. I begin with an overview of FTP, a discussion of its long history and the standards that define it. I then describe how FTP works in two subsections. The first discusses the key concepts behind how FTP functions and discusses its operation in general terms. The second provides specific details of FTP commands and reply codes. Finally, I provide a sample illustration of a user FTP session showing the internal commands used for each action.