Technology, Data Communication Terms, Glossary and Dictionary
Passive FTP is actually the normal mode of the FTP service, which is a more secure form of data transfer in which the flow of data is set up and initiated by the File Transfer Program (FTP) client rather than by the FTP server program. The other FTP mode is called the active FTP, in which the client connects from a random unprivileged port (N > 1023) to the FTP server's command port, port 21. Then, the client starts listening to port N+1 and sends the FTP command PORT N+1 to the FTP server. The server will then connect back to the client's specified data port from its local data port, which is port 20.