In extended passive mode, the FTP server operates exactly the same as passive mode, however it only transmits the port number (not broken into high and low bytes) and the client is to assume that it connects to the same IP address that was originally connected to. The syntax of the IP address and port are the same as for the argument to the PORT command.

To use passive mode, the client sends the PASV command to which the server would reply with something similar to '227 Entering Passive Mode (127,0,0,1,192,52)'.

In this case, the FTP client binds the source port of the connection to a dynamic port. In passive mode, the FTP server opens a dynamic port, sends the FTP client the server's IP address to connect to and the port on which it is listening (a 16-bit value broken into a high and low byte, as explained above) over the control stream and waits for a connection from the FTP client. The port fields should be interpreted as p1×256 + p2 = port, or, in this example, 192×256 + 2 = 49154. For example, a client with an IP of 192.168.0.1, listening on port 49154 for the data connection will send the command 'PORT 192,168,0,1,192,2'. Each field is a decimal representation of 8 bits of the host IP, followed by the chosen data port. The format for the IP and port is 'h1,h2,h3,h4,p1,p2'. In order to use active mode, the client sends a PORT command, with the IP and port as argument.

When the FTP server initiates the data connection to the FTP client it binds the source port to port 20 on the FTP server. In active mode, the FTP client opens a dynamic port, sends the FTP server the dynamic port number on which it is listening over the control stream and waits for a connection from the FTP server. Data connections usually use port number 20. The parameters for the data streams depend on the specifically requested transport mode. FTP uses out-of-band control it opens dedicated data connections on other port numbers.

A connection to this port from the FTP client forms the control stream on which commands are passed to the FTP server and responses are collected. Usually FTP servers listen on the well-known port number 21 (IANA-reserved) for incoming connections from clients. FTP runs over the Transmission Control Protocol (TCP).

File transfer system