FC4 - Firewall/Router

[Thomas Cameron]

On Sat, 2005-06-18 at 10:05 -0400, Greg Swallow wrote:

> Network 192.168.0 is configured by D-Link wireless router to cable 
> modem. firewall has access to the internet through
> the router via dhcp on eth0. eth1 is attached to what will be network 
> 192.168.1 and we want firewall to serve dhcp on
> that network. We also want firewall to route internet traffic from/to 
> 192.168.1 through 192.168.0; without having to
> shutdown the firewall server to do so.

Out of curiosity, why are you running a firewall behind the NAT router?
The NAT router is going to keep the bad guys out by its design.  Granted
it's not a really high-end security solution, but most of the NAT
routers out there today are pretty secure.

Having said that, I would set my firewall rules like this (should all be
on one line):

iptables -t nat -A POSTROUTING -s 192.168.1.0/24 -j SNAT --to-source
192.168.0.1

Save your settings by issuing the command:

service iptables save

Make sure that iptables will run next time your system boots:

chkconfig iptables on

Set your default route on the Linux firewall to be 192.168.0.1.  

Turn routing on via /etc/sysctl.conf:

net.ipv4.ip_forward = 1

Then do 

sysctl -e -p /etc/sysctl.conf

I think that's it.  Obviously, this is a very simple setup.  You can go
pretty crazy with iptables.

Holler if you need more info.

Thomas