I have a port forward to my FTP server. It is working but transfers fail. Why?

FTP uses multiple connections. If you set up a port forward for the control session (port 21) then you must also setup a port forward for the transfer sessions. You can do this in a few different ways:

1. Configure your server to use a range of ports for a transfer (for example, 10000-20000) and configure Untangle to forward all of these ports to the FTP server.
2. Use 1:1 NAT.
3. Use a Bypass Rule for the FTP server's IP address. (Please be aware that bypassing devices removes their traffic from all Untangle filtering.)