Since the government of Egypt shut off the country's Internet connectivity to the rest of the world Thursday amid violent anti-government protests, there has been a great deal of speculation in the blogosphere as to how they did it.

A basic explanation of how to block a country from the Internet is presented by The Wall Street Journal's Jennifer Valentino-DeVries. The most likely scenario in the case of Egypt, according to Jim Cowie, co-founder and CTO of Renesys Corp., is that government officials called Internet Service Providers, and the ISPs simply changed their traffic flow configurations to stop international connections. Providers in Egypt, beginning with government-owned Telecom Egypt, started turning off their networks at around midnight Thursday. There are only four large ISPs in Egypt, and so it wouldn't take a lot of phone calls to bring the system to a standstill. By Friday night, 93 percent of Egypt's networks were not reachable, according to Renesys.

The nuts and bolts of disconnecting a country from the Internet are explored in greater detail by Iljitsch van Beijnum at Ars Technica. Van Beijnum points out that just because connectivity is blocked to the rest of the world, Internet users Egypt wouldn't necessarily be cut off from each other. To break the links between the ISPs in Egypt, authorities would have had to order a separate series of steps.

One service provider in Egypt, the Noor Group, reportedly retained connectivity during the chaos. As CNET's Declan McCullagh reports, the speculation is that the Noor Group's clients are to big to disconnect. In addition to the Egyptian stock exchange, the ISP boasts numerous multinational corporations as customers, including ExxonMobil, Coca-Cola, Pfizer, Fedex, Nestle and Toyota. 

For more:
- see Jennifer Valentino-DeVries' article at The Wall Street Journal
- see Iljitsch van Beijnum's post at Ars Technica
- see Declan McCullagh's article at CNET

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