At work, we have an IP network called BARONET. It's like the Internet except it's not. There is a bridge on one machine that proxies HTTP requests from this network to the Internet. There are no routes to the Internet.
This significantly reduces the possibility of "cyberattacks", since you'll have to go through that proxy box. (Which probably runs Windows, but hey... if you actually cared about security, you wouldn't do that. The rest of the idea is good.)