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How Pakistan knocked YouTube offline (and how to make sure it never happens again)
Written by Daniel   
Saturday, 01 March 2008 14:11

 How Pakistan knocked YouTube offline (and how to make sure it never happens again)

February 25, 2008 2:30 PM PST
Posted by Declan McCullagh
C/Net News

 A high-profile incident this weekend in which Pakistan's state-owned telecommunications company managed to cut YouTube off the global Web highlights a long-standing security weakness in the way the Internet is managed.

After receiving a censorship order from the telecommunications ministry directing that be blocked, Pakistan Telecom went even further. By accident or design, the company broadcast instructions worldwide claiming to be the legitimate destination for anyone trying to reach YouTube's range of Internet addresses.

The security weakness lies in why those false instructions, which took YouTube offline for two hours on Sunday, were believed by routers around the globe. That's because Hong Kong-based PCCW, which provides the Internet link to Pakistan Telecom, did not stop the misleading broadcast--which is what most large providers in the United States and Europe do.

This is not a new problem. A network provider in Turkey once pretended to be the entire Internet, snarling traffic and making many Web sites unreachable. Con Edison accidentally hijacked the Internet addresses for Panix customers including Martha Stuart Living Omnimedia and the New York Daily News. Problems with errant broadcasts go back as far as 1997.

It's also not an infrequent problem. An automatically-updated list of suspicious broadcasts created by Josh Karlin of the University of New Mexico shows apparent mischief--in the form of dubious claims to be the true destination for certain Internet addresses--taking place on an hourly basis.

So why hasn't anyone done something about it? False broadcasts can amount to a denial-of-service attack and, if done with malicious intent, can send unsuspecting users to a fake bank, merchant, or credit card site.

To understand why this is both a serious Internet vulnerability and also difficult to fix requires delving into the technical details a little.

How to pretend to be
When you type a domain like "" into your Web browser, it uses the Domain Name System to cough up a numeric Internet address, which in our case is That IP address is handed to your router, which uses a table of addresses to figure out the next hop toward the server.

Network providers--called autonomous systems, or ASs--broadcast the ranges of IP addresses to which they'll provide access. One of the functions of the Internet Corporation for Assigned Names and Numbers is managing the master list of AS numbers, which it does by allocating large blocks of 1,000 or so at a time to regional address registries.   [C/Net News...]  [Comments...]

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