Re: Port Forwarding

[Nathan Barham <nathan@sleepygeek.com>]

Dominique Benz wrote:
> Hello List!
>
> I'm a little new in the world of iptables and could need some advice
> concerning a simple Port Forwarding. I created s basic rule set as described
> in common howtos and the internet:
>
> # iptables -A FORWARD -i eth0 -p tcp --dport port -j ACCEPT
> # iptables -t nat -A PREROUTING -i eth0 -p tcp --dport port -j DNAT --to
> local_ip:port
>
> My FORWARD CHAIN contains two further entries (they actually don't affect
> the above rules):
>
> # iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT
> # iptables -A FORWARD -i eth0 -o eth1 -m state --state ESTABLISHED,RELATED
> -j ACCEPT

Assuming port forwarding is turned on . . . for reference, here are 
rules for forwarding incoming SMTP which work for me.  They look a lot 
like yours.

# PREROUTING
$IPTABLES -t nat -A PREROUTING -p tcp -i $EXT_IF -d $SMTP_IP --dport 25 
-j DNAT --to-destination $DMZ_SMTP_IP


#FORWARD
# Let already established forwarded conversations continue.
$IPTABLES -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT


$IPTABLES -A FORWARD -i $EXT_IF -o $DMZ_IF -p tcp -d $DMZ_SMTP_IP 
--dport 25:25 -j ACCEPT