- In active mode the FTP server will try to make the request to the client side ports incremented by 1. For example, client connects to the FTP server using port 21. Once, the connection will be established the server will continue looking for the open ports > 1023 of client. Active FTP is more beneficial to the FTP server admin, but detrimental to the client side admin. It is because the server will continue looking for the open ports on client side which would almost certainly be blocked by a firewall on the client side.
Passive mode for FTP:
Passive FTP is beneficial to the client, but detrimental to the FTP server admin. The client will make both connections to the server, but one of them will be to a random high port, which would almost be blocked by a firewall on the server side.