If the server is behind a firewall you wont see the server since the router/gateway needs to be set up to forward all FTP port requests to the appropriate server on the local network.

Remember, you address the FTP server on the local network using a private IP address and when you are on the internet you address the public IP address of the networks gateway/router.

Setup your gateway/router to forward all FTP connection requests to your FTP servers private IP address. Another way is to connect the FTP server to the DMZ port on the router for full internet exposure but this is not recommended since it is a security risk.

Brian Seekford