pureftpd and my router

This is probably not a Mac-specific question, but I'm hoping someone here can tell me how to deal with it anyway...

I just installed pureftpd (Mac OS X 10.6); I'm running a home network through a Verizon FIOS router. I've gotten as far as getting the FTP requests to my machine, and I can successfully work using ftp localhost. When I try an anonymous login through my external IP address, I can log in successfully, but everything else fails with messages like below. I've tried starting the server with and without -N, with no obvious effect. Any advice?

src [518]> ftp xxx.xx.xxx.xxx
Connected to xxx.xx.xxx.xxx.
220---------- Welcome to Pure-FTPd [TLS] ----------
220-Local time is now 11:15. Server port: 21.
220-IPv6 connections are also welcome on this server.
220 You will be disconnected after 15 minutes of inactivity.
Name (xxx.xx.xxx.xxx:me): anonymous
230 Anonymous user logged in
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> ls
500 Unknown command
500 I won't open a connection to 192.168.1.4 (only to xxx.xx.xxx.xxx)
425 No data connection
ftp>

What ports have you forwarded.... You will need 20 and 21 opened to that machine if you are using passive mode.

Did you open port 20?

http://slacksite.com/other/ftp.html

edit: or try passive mode?

LOL, I just noticed that I type passive.... I meant active. 20 and 21 for active 21 for passive only and the server has to support it.