Only PASV is successful

[cindyh]

From the client application on a server that I don't manage, I am able to open an FTP session on my Ability FTP server only if I use PASV mode. Tell me why this might be. I am in a campus setting where there are various firewall restrictions, but I am told port 21 is open. Do I need other ports for non-PASV? The box that I'm using as a client does not support PASV within the application that I'm FTPing from.

[Code Crafters]

You have to use PASV mode if your FTP client is behind any firewalls. Only if you have no firewalls on your client side (usually internal LAN connections only) can you use non-PASV mode as non-PASV mode requires the client to open a data channel connection which obviously won't be allowed through its firewalls whereas the PASV port range can be let through for data channels opened on the server side.