FTP port connection behind NAT

[Yo mismo]

I have a net with nat connection to internet installed in windows 2003.
From client machine I can connect to a FTP server with a port connection,
but I can´t execute LS command.
If I connect to FTP server from Nat Server, I can execute LS command.
What can I do in nat server to do this?

Thanks

 

[Steven L Umbach]

I have not tried that setup myself but see the link below for firewall/packet
filtering for ftp and it's challenges. Port 20 tcp is used for data channel and port
21 tcp is used for control channel.--- Steve

http://www.isaserver.org/articles/How_the_FTP_protocol_Challenges_Firewall_Security.html