File Transfer Protocol (FTP)

Definition of File Transfer Protocol (FTP) in The Network Encyclopedia.

What is File Transfer Protocol (FTP)?

An Internet standard application-level TCP/IP protocol that can be used for transferring files between hosts on a TCP/IP internetwork.

How It Works

File Transfer Protocol (FTP) is one of the earliest Internet protocols, and is still used for uploading and downloading files between clients and servers. An FTP client is an application that can issue FTP commands to an FTP server, while an FTP server is a service or daemon running on a server that responds to FTP commands from a client. FTP commands can be used to change directories, change transfer modes between binary and ASCII, upload files, and download files.

Graphic F-13. File Transfer Protocol (FTP).

FTP uses Transmission Control Protocol (TCP) for reliable network communication by establishing a session before initiating data transfer. TCP port number 21 on the FTP server listens for connection attempts from an FTP client and is used as a control port for establishing a connection between the client and server, for allowing the client to send an FTP command to the server, and for returning the server’s response to the command. Once a control connection has been established, the server opens port number 20 to form a new connection with the client for transferring the actual data during uploads and downloads.


Internet Information Services (IIS) supports virtual servers and virtual directories using FTP.


You can view the status of open ports on IIS using the netstat command. If an FTP client has trouble accessing information on IIS, try changing the directory listing style for the FTP service on IIS. FTP supports only Basic Authentication or anonymous access for authentication schemes and does not support the more secure Microsoft Windows NT Challenge/Response Authentication method.