rt-n66w

Not sure I'm putting this question in the right subforum, so many to chose from. I'm on a Asus RT-N66W (same as RT-N66U, just different colour) with AsusWRT-Merlin firmware. It has a function to work as a FTP server through Asus DDNS (myusername.asuscomm.com) but even though I run a VPN client...