How Egypt Cut Off the Internet (and How a U.S. ‘Kill Switch’ Might Work)

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Egypt’s Border Gateway Protocol Addresses

Egypt’s been able to effectively remove itself from the internet by pulling its normally visible routes from the BGP routing table. The IP addresses that identify computers connected to the internet through all of Egypt’s ISPs are now basically invisible to the outside world. Computers inside the country are currently sort of like houses with no mailboxes that aren’t on any map.

The Kill Switch

While images of a big red button housed inside a Plexiglass case that can only be unlocked by two simultaneous key twists of top government officials seem to fit the idea of how such an internet kill switch would work, the reality is far more mundane. In Egypt’s case, the internet service providers that operate within the country agree to let the government shut down commonly-used connection protocols if they see fit to do so.

The BBC reports that one of Egypt’s big internet service providers, Vodafone, issued an e-mail statement simply stating that the company was instructed to shut down its connections. "Under Egyptian legislation the authorities have the right to issue such and order and we are obliged to comply with it," said the statement.

The same order was almost certainly issued to all the other internet service providers operating inside Egypt and, just like that, the internet went down.

UPDATE

As many of you have pointed out, it’s not simply the DNS servers that have been shut down in Egypt as this original post suggested. The Border Gateway Protocol (BGP) routing table routes have been taken offline in Egypt and I have re-written large chunks of this post to reflect that.

Ars Technica sums up the situation well:

"What BGP does is ‘advertise’ the local address prefixes to neighboring networks. Wholesale ISPs propagate their customer’s advertisements to their neighbors so that eventually all ISPs know all other ISPs’ prefixes. This enables routers to know where to send packets with a given destination address. The 3,500 Egyptian prefixes are now no longer advertised, so they’re missing from the routing tables of BGP routers around the world. This means that routers no longer know where to send packets addressed to IP addresses that fall within these prefixes—even if all the cables are still working fine."

Renesys’ initial blog post is continually being updated as well. My apologies for the incorrect information—I’d grabbed the information about the DNS servers being shut down from this BBC post but it’s clear that Egypt’s internet access has been cut off directly at the routing table level.

Thank you to everyone for clearing this up.

More on TIME.com:

Internet Rallies Behind Egypt In An Attempt To Restore Communication

Did Egypt Really ‘Shut Off’ the Internet?

As Clashes Continue, Why Fear of Islamists Paralyzes the U.S. on Egypt

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