Router for internal network

[BitPusher16]

I am creating a test lab for network experiments. A, B, and C are all on an internal network. C has two connections, one internal network connection and one NAT connection which allows it internet access.

I would like C to function as a router for the internal network. So far, I can ping between A, B, and C on the internal network. I can also ping from C to the internet (google.com). What are the high level steps to configure C as a router that will allow A and B to access the internet?

I am using Lubuntu as my guest OS.

I have configured A, B, and C to use static IP addresses on the internal network. C uses DHCP on the NAT connection.

I have tried to follow the steps to configure C as a router:
http://askubuntu.com/questions/590920/u ... a-firewall
Specifically, I have modified /etc/network/interfaces and /etc/sysctl.conf as indicated.

If there are in-depth guides (or textbooks) which could help answer my question, I would be grateful to have links to these as well. Googling on the internet for several hours has not been very fruitful.

Thanks much!

[BillG]

The best way is to run a router appliance like pfSense in the vm rather than install router software in some other OS. It will do NAT pretty much as the default setup.