CentOS - Oct 2009 - Can't get forwarding to work

Hello all:

I am having trouble getting port forwarding
with iptables to work.

I have this configuration:

Internet --- Linux machine --- Windows machine

The windows machine is set up to listen on 
IP address 10.0.0.31

I am able to use lynx to connect to http://10.0.0.31 on 
the linux machine so there is no problem going from
the linux machine to the windows machine.

I have tied a public IP address a.b.c.d to the
linux machine and entered these rules in its
firewall:

/sbin/ifconfig eth0:1 $WIN_EXTERNAL_IP netmask $ETH0_NETMASK broadcast
$ETH0_BCAST
/sbin/iptables -t nat -A PREROUTING -p tcp -i eth0 -d $WIN_EXTERNAL_IP
--dport 80 -j DNAT --to $WIN_INTERNAL_IP:80
/sbin/iptables -A FORWARD -p tcp -i eth0 -d $WIN_INTERNAL_IP --dport 80 -j
ACCEPT

I have this log entry at the bottom of the firewall rules:

/sbin/iptables -A FORWARD -j LOG --log-prefix "FORWARD "

When I try to go to the external IP address http://a.b.c.d from
another network, I get an error.

Any ideas?

Thanks,
	Neil

--
Neil Aggarwal, (281)846-8957, www.JAMMConsulting.com
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> Hello all:
>
> I am having trouble getting port forwarding
> with iptables to work.
>
> I have this configuration:
>
> Internet --- Linux machine --- Windows machine
>
> The windows machine is set up to listen on
> IP address 10.0.0.31
>
> I am able to use lynx to connect to http://10.0.0.31 on
> the linux machine so there is no problem going from
> the linux machine to the windows machine.
>
> I have tied a public IP address a.b.c.d to the
> linux machine and entered these rules in its
> firewall:
>
> /sbin/ifconfig eth0:1 $WIN_EXTERNAL_IP netmask $ETH0_NETMASK broadcast
> $ETH0_BCAST
> /sbin/iptables -t nat -A PREROUTING -p tcp -i eth0 -d $WIN_EXTERNAL_IP
> --dport 80 -j DNAT --to $WIN_INTERNAL_IP:80
> /sbin/iptables -A FORWARD -p tcp -i eth0 -d $WIN_INTERNAL_IP --dport 80 -j
> ACCEPT
>
> I have this log entry at the bottom of the firewall rules:
>
> /sbin/iptables -A FORWARD -j LOG --log-prefix "FORWARD "
>
> When I try to go to the external IP address http://a.b.c.d from
> another network, I get an error.
Do you have return POSTROUTING rules in your iptables nat table, have you 
enabled ip forwarding?