YouTube was back up two hours after Pakistan, in an act of information provincialism, inadvertently made the video-sharing site inaccessible to users around the world Sunday.
The blackout left network administrators and Internet activists wondering on Monday how Pakistan's actions, meant to restrict only its citizens from accessing YouTube, could have such widespread reverberations — and whether such a disruption could be reproduced by someone with more malicious intent.
The incident began Friday, according to reports, when the Pakistani government of Pervez Musharraf became worried that a video clip attacking Islam might generate unrest among its Muslim population. The government asked the Pakistan Telecommunication Authority to cut off access to YouTube for the country's estimated 8.2-million Internet users.
But two critical errors allowed Pakistan's action to echo around the globe for at least a brief period on Sunday afternoon, according to Martin Brown, a data engineer at the Renesys Corp., an Internet monitoring company.
As part of its effort to block YouTube within the country, Pakistan Telecom created a dummy route that essentially discarded YouTube traffic, sending it into what Internet experts call a black hole.
Pakistan Telecom then made an error by announcing that dummy route to its own telecommunications partner, PCCW, based in Hong Kong, shortly before noon EDT Sunday, according to Renesys.
PCCW then made a second error, accepting that dummy route for YouTube and relaying it to other Internet providers around the world.
Internet service providers now had two conflicting online "roads" leading to YouTube. But because an important online protocol called Border Gateway Protocol favors longer routing addresses — they are thought to be more specific — at least 97 major Internet providers and thousands of smaller ones chose the dummy route, Pakistan's black hole.
About 1 p.m. Sunday, according to Renesys, YouTube began working to correct the error. YouTube has removed the video clip cited by Pakistani officials.