A country can largely shut themselves off, which China and Russia largely already do. But the collection of networks is so large that it's hard for others to shut them off. The hackers in those bad countries can therefore poke sticks out of their cage pretty easily. The following is from "How could the internet be shut off?'
Jeremy Straub
Assistant Professor of Computer Science and Associate Director of the North Dakota State University Institute for Cyber Security Education and Research
There isn’t some gigantic on-off switch: The internet is a diversified platform, a lot of different networks connected to each other, so there’s no good way to turn it off.
Fundamentally, you have to think back to the original conception of the internet, which was to try to create a distributed network that could survive attacks on different government or military installations. It was designed to be resilient to external threats—but not necessarily to internal or peer-level threats, which is where you probably see the greatest potential risk factors.
When certain countries have tried to turn the internet off—in the whole country or in specific regions—they use techniques that basically interfere with or deny some of the services that people use online, or they take control of the actual pipeline to the rest of the world. The Great Firewall of China is an example of the latter—they filter the web, looking for things that are not appropriate. On the other hand, when people have tried to turn off the internet in just one region, or deny access to particular groups, that has typically been accomplished through interfering with a service such as DNS, to make it so that, for at least those that don’t have a ton of technical knowledge, the internet just looks like it’s not working, even though you might have a lot of what is actually needed to have an internet connection. Denying critical services reduces the ability of the internet to work for most people, and makes large coordination a problem.
Certainly, there’s a lot of stuff on the internet that isn’t critical infrastructure—these are things that are ancillary, but which many people would consider important communications channels. Things like Facebook, for instance. Nobody’s going to immediately get injured or die if Facebook went offline—but it might push traffic that’s typically on that platform to a different platform, like the telephone, which might not be able to handle that influx.
More important are the critical infrastructure systems—things which, if they stopped working, would cause immediate danger. For instance, gas and power in the winter, or keeping reactors in check, and making sure water systems are working. The internet being knocked out isn’t going to cause the power to shut down—but knocking out the power is going to knock out the internet. So if somebody was really trying to deny internet access in an area, they might make that their target.
The next tier would be commercial systems—if a company’s website goes offline, it’s not going to cause famine, or injure or kill someone, but it could be very detrimental.
