How does Passive FTP work?
http://www.velikan.net/iis-passive-ftp/ How does Passive FTP work? In passive mode FTP the client initiates both connections to the server, solving the problem of firewalls filtering the incoming data port connection to the client from the server. When opening an FTP connection, the client opens two random unprivileged ports locally (port number > 1023 and port number+1). […]