Per suggestions from the list, I tried setting Pure-FTPD. I used the "-P ext.nat.ip.addr" argument, and that seemed to make things work (at least from the first external host I tested from). Well... mostly. It seems that most networks can correctly interface with my port 20 FTP data channel, but not all.
Ironically, the user for whom I set the server up in the first place, is the one that reported this to me: when he tries to FTP from home, it does the port 20 hang; when he FTPs from work, it works just fine. Oddly enough, he's using his notebook computer at both places, and therefore using the same FTP client and settings. I also ran into a variant of this problem at work. I can access 21 on my FTP server, but not 20. Yet, I can access both 20 and 21 on other hosts. It's a mind bender. -tom
