FTP with iptables

[muffinman666@gmx.net]

Hi.

We set up a firewall with iptables and the following settings (as given by "iptables -L"):

Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy DROP)
target     prot opt source               destination
ACCEPT     tcp  --  anywhere             anywhere           tcp dpt:ftp
ACCEPT     tcp  --  anywhere             anywhere           tcp dpt:smtp
ACCEPT     tcp  --  anywhere             anywhere           tcp dpt:http
ACCEPT     tcp  --  anywhere             anywhere           tcp dpt:pop3
ACCEPT     tcp  --  anywhere             anywhere           tcp dpt:https
ACCEPT     all  --  anywhere             anywhere           state RELATED,ESTABLISHED

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination


So, we setup a FTP-Server on a suse mashine to test the ftp connection. We use the proftpd and 
the connection is fine. But with other FTP-Servers over the world (for example ftp.kernel.org) 
it is not possible to do any file transfers. No listing is shown, it seems to be a file transfer 
over the data channel, too. 
Here is the error:

Connected to ftp.kernel.org, waiting for response...
< 220 ProFTPD [ftp.kernel.org]
> USER anonymous
< 331 Anonymous login ok, send your complete email address as your password.
> PASS *****
< 230 Anonymous access granted, restrictions apply.
> REST 1
< 350 Restarting at 1. Send STORE or RETRIEVE to initiate transfer.
> REST 0
< 350 Restarting at 0. Send STORE or RETRIEVE to initiate transfer.
> SYST
< 215 UNIX Type: L8
> PWD
< 257 "/" is current directory.
~ Login completed.
> PORT 192,192,192,220,6,106
< 500 Illegal PORT command.
~ Could not retrieve directory listing for "/"

What can we do to solve this problem?

Thanks a lot for your help, 

The Muffinman