So how do you shut off a whole nation's Internet?

To silence dissidents, the Egyptian government made a move Thursday that has no precedent: It turned off the Internet nationwide. How did they do it — and could the same thing happen here?
According to David Clark, an MIT computer scientist whose research focuses on Internet architecture and development, a government's ability to control the Internet depends on its control of Internet Service Providers (ISPs), the private sector companies that grant Internet access to customers.
"ISPs have direct control of the Internet, so what happens in any country depends on the control that the state has over those ISPs," Clark told Life's Little Mysteries in an e-mail. "Some countries regulate the ISPs much more heavily. China has in the past 'turned off' the Internet in various regions."
When a government orders the ISP to disable service, Clark explained, "they have lots of ways of doing it technically. They could power down devices (which is sort of like unplugging things), or change the routing tables (which is more like a "digital kill," and can serve to allow selective services to stay up)."

malletzky wrote:I read in the german newspapers that this issue has been discussed here too, and I remember that one of the explanation given was that this is really possible according to some laws in Egypt. The government can and did order on thursday, especially from the british Vodafone as one of the main internet provider, to cut the internet down.

They HAD to follow the order...otherwise, they would face huge problems with braking the law.