i'm using 3.3.1 which I received from the nice draytek people (even before it was released to the general public). it solved a problem i had at the time, between priorities of DMZ and open ports configuration.

off_topic:
nice to know: open ports configuration of machine A takes priority over DMZ configuration of machine A. So if trying a DMZ solution (usually as a last resort), do not forget to REMOVE or at least DISABLE the open ports configuration line
/off_topic.

anyway, tnx for the tip. I'll give Wireshark a try. I'm a Windows server expert, I'm not a network man, although I wish I was at the moment :wink: I'm simply going nuts over the fact that it worked perfectly with my 2600, and not with the 2820n... I'm convinced I'm missing something so obvious....

I upgraded the firmware to 3.3.2.1 (july 24, 2009).
I had no success with the sniffer (not really sure what to look for)
I tried open ports, changing the ftp server to standard port 21, disabled PASV, and as a last resort DMZ.
guess what, even DMZ did not work (I disabled open ports first).
I'm truly at a loss over this one.
and guessing from the amount of replies, there's not a lot of people that are this deep into Draytek's wonderful world

what I did "accidentally" tried is this:
C:\Users\user>ftp
ftp> open 10.10.10.1 // this is my LAN's first IP, i.e. my Draytek
Connected to 10.10.10.1.
220 FTP version 1.0
User (10.10.10.1:(none)):
331 Enter PASS command
Password:
230 Logged in
ftp> ls -al
550 No ChartsTable or Device disconnected
550 No ChartsTable or Device disconnected
ftp>

could it be, that Draytek's internal handling of the FTP protocol is blocking the FTP server inside my LAN?

solved
upgraded firmware but that was not enough, needed to restore factory default settings (.rst) and started from the beginning. within 5 minutes things worked as they should have from the start, with the same configuration as before.
lesson to be learned: if router does things it is not supposed to do, upgrade firmware to latest version, RESET EVERYTHING, and start from the beginning. takes some time, but in the end it is faster.

/closed.