Have been using Debian squeeze + ISPConfig3 (also) as ftp/SSH-server long time with FileZilla w/o an issue.
i.e. Filezilla is actively replacing local IP with given (public) IP and connection works just fine.
(This one is running on physical server, planning to move to VM (Debian) in future...)
Now when trying to test some other S/W to make (WIN) back-ups (e.g. Duplicati), I face problems with them as they don't replace local IP in passive mode (ending to connection failure)
Tried to google as well, but did not find nice solution for Dynamic-IP (my ISP cannot provide static-IP...). Anyone with good solution? Current public-IP avail. e.g. from http://checkip.dyndns.org/