FTP / SSL working internally but stopping at Listing Directory


We have a basic FTP server which runs FTP / SSL on port 21, it works fine internally and almost externally apart from the fact it wont list the directories, I have all the firewall rules correct as it is connecting just not listing the directories.

I have heard this has something to do with Passive/Active modes and NAT but as this is the first FTP / SSL system I have built I am not sure how to get this sorted.

FYI: this runs on a DC with only IIS FTP services installed.
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Giovanni HewardCommented:
FTP uses two ports, a control port and a data port.  You'll need to open additional ports, depending on whether you're supporting active mode, passive mode, or both.

Active Mode
Passive Mode
Active requires both 20/TCP and 21/TCP.

Passive requires a defined data channel port range...

Enter a range of values for the Data Channel Port Range.
This works internally because you do not have an internal firewall blocking 21/TCP and 20/TCP (active)  or 21/tcp and the predefined data channel range (passive).

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mfg1Author Commented:
Since this post we have tried the options you mentioned above, but we are still having issues with the directory listing,  we do t use the local windows firewall on this server and we have specified the dynamic port range and allowed through our hardware firewall.

Still cannot list the directories. Also I have open ports 20,21.
Giovanni HewardCommented:
Try enabling logging on your firewall to see what data port(s) are being blocked.  Did you try switching between active and passive mode using the FTP client when testing?  If you intend to support both modes, try performing a directory listing with both modes when logging at the firewall.  

Alternatively, you can run TCPView on both sides (server and client) to see what connections are attempted when performing a directory listing.
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Windows Server 2012

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