No access to the folders of an FTP Server: 425 Can't open data connection for transfer of "/"

From a private Zone (such as LAN, DMZ) it's possible to get access to the FTP Server, but from the Wan Zone the access to the folders is denied.

If you run a packet capture, the packets should be correctly forwarded to the Server but the FTP Server should display an error as shown below:

425 Can't open data connection for transfer

It could be possible that the FTP Server doesn't accept an inbound connection from a source IP address that is Public.

Be sure to configure the FTP Server as shown in the following guide:

Configuration for a Passive Mode FTP Server behind the SonicWall. (SW10090)

A workaround would be to change the public source IP to a private source IP using a NAT policy.

Example below:

Original Source  : ANY

Translated Source : A private IP address

Original Destination  : FTP Server Public (typically X1 or a WAN interface)

Translated Destination  : Private IP address FTP Server

Original Service  : FTP Custom Group

Translated Service  : ORIGINAL

Inbound Interface  : X1 (or the WAN interface used)

Outbound Interface  : Any

You should now be able to get access to the folders of the FTP Server.