6.5. IP Masquerading multiple internal networks

Masquerading more than one internal network is fairly simple. You need to first make sure that all of your networks are running correctly (both internal and external). You then need to enable traffic to pass to both the other internal interfaces and to be MASQed to the Internet.

Next, you need to enable Masquerading on the INTERNAL interfaces. This example uses a total of THREE interfaces: eth0 is the EXTERNAL connection to the Internet, eth1 is the network, and eth2 is the network. Both eth1 and eth2 will be MASQed out of interface eth0. In your rc.firewall ruleset next to the existing MASQ enable line, add the following:

Please note that it is CORRECT to have "eth0" specified multiple times for the exmples shown above. The reason for this is the Linux kernel needs to know which interface is used for OUTGOING traffic. Since eth0 in the above examples is the Internet connection, it is listed for each internal interface.