Redirect ftp traffic to an IIS4 ftp server

Hi all, I'm using SuSE 6.4 with firewals-2.0-12. I need to redirect outside ftp traffic to an internal iis4 ftp server. Let said that the external address of the firewall is 12.34.56.80 and the address of the internal ftp server is 172.20.0.80. I use Rinetd to redirect the traffic with the following line : 12.34.56.80 20 172.20.0.80 20 12.34.56.80 21 172.20.0.80 21 I try to connect to the server using CuteFTP. In PASV mode, it says "Connection data socket..." but it never get through. And in active mode, it says "500 Invalide PORT Command". I know that in rinetd manual, it says that rinetd cannot redirect ftp traffic because it uses more than one socket. Is there any solution, without changing to whole thing? Thanks Ka Kit Yick