How can an entire country be taken offline?

The answer depends on the country. In countries such as Syria, which went offline last week, Internet connectivity is so centralized that unplugging a few routers could take nearly everyone offline. By contrast, blacking out the United States probably requires a virtually endless game of Whac-A-Mole to shut down thousands of independent providers. Read related article.

How are we connected?
In its simplest form, the Internet is a huge collection of computers and routers. "You plug things together and when you're done, you end up with the Internet," said Marty Lindner, principal engineer with the CERT computer security program at Carnegie Mellon University. Shutting down a home user, a company or a country merely requires disconnecting the right group of routers or cables.

Local networks
All computers with Internet access in every organization — whether a school, a company or a country — are connected to a local network. Local networks connect to Internet service providers through routers.

Internet service providers
Data flows back and forth through ISPs (the Internet's "backbone") to networks in the rest of the world. Most international Internet traffic goes through undersea cables.

Illustrations are schematic.

How hard would it be to disconnect us?
Internet measurement company Renesys rated countries' risk of being disconnected from the Internet based on the number of providers offering pathways outside the country. Renesys considered Syria a severe risk for shutdown because nearly all its connectivity goes though a state-run ISP, the Syrian Telecommunications Establishment.

SOURCES: Marty Lindner, principal engineer with the CERT Program of the Software Engineering Institute at Carnegie Mellon University; James Cowie, Chief Technical Officer of Renesys; CloudFlare. GRAPHIC: Bonnie Berkowitz, Bill Webster - The Washington Post. Published Dec. 4, 2012.