[NTLUG:Discuss] Iptables NAT not working and no logs

[Neil Aggarwal]

Hello all:

I am having trouble getting NAT with iptables to work.

I have this configuration:

Internet --- Linux machine --- Windows machine

The windows machine is on a private IP.

I am able to go to the linux machine and load the
web site from the windows machine using lynx with
the private IP.  That means there should not be a
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:

echo "1" > /proc/sys/net/ipv4/ip_forward
/sbin/ifconfig eth0:1 $WIN_EXTERNAL_IP netmask $ETH0_NETMASK broadcast
$ETH0_BCAST
/sbin/iptables -t nat -A PREROUTING -d $WIN_EXTERNAL_IP -j DNAT --to
$WIN_INTERNAL_IP
/sbin/iptables -t nat -A POSTROUTING -s $WIN_INTERNAL_IP -j SNAT --to
$WIN_EXTERNAL_IP

I have these log entries at the bottom of the firewall rules:

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

INPUT, OUTPUT, and FORWARD are set to default DROP.
The nat tables are all set to default ACCEPT.

When I try to go to the external IP address http://a.b.c.d from
another network, it does not connect and I do not see anything
in the firewall logs.

Any ideas?

Thanks,
	Neil



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Neil Aggarwal, (281)846-8957, www.JAMMConsulting.com
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