If you want to run an FTP server, this is how you do it:
In the router:
- Forward port 21 to your computer on TCP.
- Forward range of ports (like 10001-10100) to your computer on TCP. This is you PASV range.
In the server:
- Set the server to listen to port 21 (usually default).
- Set the server to use the ports above (10001-10100) for PASV (passive) connections.
- Set the server to listen to the IP that is your external IP.
You may not be able to connect from the inside of the network though, unless you connect to the external IP!