FTP NAT FIREWALL

Hi all, I'm sorry I will post a question I saw hundreds of time but I
have not found an answer for me.

I have a linux firewall, clients on private LAN. They must connect to
a pubblic ftp server on internet which use non-standard ports. I have
loaded ip_conntrack, ip_conntrack_ftp and ip_nat_ftp but clients
cannot do a get because "Can't build data connection: 10060". I tried
also loading ip_conntrack and ip_nat_ftp with ftp non-standar ports
specified with no results. Everything works with other ftp server on
public internet with standard ports.

Can anyone help me to understand the problem and the solution, of
course.

Bye