The following will grant masquerading functionality, but will not provide a fully-configured firewall.

In this example, we will use device eth0. The following command will begin the configuration of iptables by setting up post routing with the masquerading target:

Edit the /etc/sysctl.conf file to set-up ipv4 forwarding by changing the line which reads:

If that line does not exist, simply add the above line which sets the ip_forward value to 1 (one). Then run the following command which will reread your sysctl file:

Additional information on how to use iptables and how to save iptables configuration can be found in other Knowledge base articles. For additional options and usage for the iptables command, see the man page by executing man iptables from the command line.