Windows IIS’s FTP server is configured to use ports 1025-5000 for Passive FTP traffic by default. You can follow the steps at Microsoft’s support page to change the Passive FTP port range.

To enable Passive FTP, Windows Firewall must be configured to allow traffic from these ports. After verifying that the above port range is what you would like open to FTP traffic, each port number must be opened one by one. However, a simple script to automate this process is described here.

And here is a random link (ok, the link itself isn’t random, but the link behind the link is).