vsftpd - private IP vs. public IP

[pinenut]

Hi,
I've set up a home network with a computer running FC4 and another WindowsXP.

My FTP server under Linux is vsftpd 2.0.3. From the WinXP box, I can connect to the ftp server with the local private IP address (ie. 192.168.1.118) with a user name and its password and upload and download files. But with the public IP, ftp.xxxx.org, I am able to connect to the server but get disconnected immediately with an error message, an established connection was aborted by the software in your host machine.

What would cause this problem?

pinenut

[loudnoises]

do you have a firewall enabled on your public side? If so, you will need to open udp 21 and 20. 21 is ftp listen and 20 is ftp data