From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrea Rossato <mailing_list@istitutocolli.org>
Subject: Re: portfw on iptables 2.4 kernel problem.
Date: Wed, 11 Dec 2002 12:26:17 +0100
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louie miranda wrote:
> I have an internel ftp server w/c i want to access over my linux router(gw)
> Its internel IP is 10.0.0.11 and port 21. My externel IP lets say
> 203.100.100.1.


echo "1" > /proc/sys/net/ipv4/ip_forward
iptables -A FORWARD -d 10.0.0.11 -j ACCEPT
iptables -A FORWARD -s 10.0.0.11 -j ACCEPT

iptables -A PREROUTING -t nat -p tcp -d 203.100.100.1 --dport 21 -j DNAT 
--to 10.0.0.11
ptables -t nat -A POSTROUTING -o eth1 -j SNAT --to-source 203.100.100.1


tha should work: it's working for me, at least.
Remember that forwarded traffic must be SNATed with the source (public) 
address of the forwarding box.
andrea