Paksitan has lifted a ban it imposed on YouTube on Sunday, YouTube has said.
The ban was reportedly imposed by the Pakistan Telecommunication Authority on Sunday in response both to a film preview by Dutch MP Geert Wilders, which some Muslims may have found offensive, and in reaction to protests against Danish publications reprinting cartoons that some Muslims found controversial.
A YouTube spokesperson said on Wednesday: "We are pleased to confirm that YouTube is again accessible in Pakistan." The spokesperson declined to comment as to why the ban had been lifted.
The ban had the side effect of knocking YouTube off the internet for two hours on Sunday said YouTube owner Google, which blamed the outage on traffic being routed via "erroneous protocols".
"For about two hours [on Sunday], traffic to YouTube was routed according to erroneous internet protocols, and many users around the world could not access our site," said a Google spokesperson. "We have determined that the source of these events was a network in Pakistan. We are investigating and working with others in the internet community to prevent this from happening again."
The results of the Google investigation are unlikely to be made public, according to the Google spokesperson.
However, there are different reports as to the cause of the outage. The BBC reported that Hong Kong-based internet protocol backbone company PCCW, which provides upstream internet access to many of Pakistan's ISPs, had "leaked" details of the ban to ISPs around the world, which had then mistakenly blocked YouTube.
PCCW denied that it had been responsible for the outage, telling ZDNet.co.uk on Wednesday that the actions of a downstream customer had caused the outage.
"PCCW Global operates a large resilient global IP backbone network with many national service providers worldwide as customers," said an email statement sent to ZDNet.co.uk by a PCCW spokesperson. "One of [PCCW's] downstream customers erred in routing configuration in a manner that apparently affected YouTube traffic. PCCW Global acted swiftly to correct the problem by disconnecting the source network which allowed immediate traffic normalisation."
Researchers at security company Arbor Networks said YouTube could have been knocked out by ISPs in Pakistan announcing to a Border Gateway Protocol (BGP) community that it was blocking YouTube.
A Pakistani ISP could have statically routed YouTube IPs to a null or discard interface on its routers, according to a blog post by Arbor Networks chief research officer Danny McPherson. However, this could have resulted in redistribution of all configured static routes into sets of globally advertised BGP routes, redirecting all YouTube traffic to the null interface.
"The net-net is that you're announcing reachability to your upstream for 220.127.116.11/24 [YouTube IP addresses], and your upstream provider, who is obviously not validating your prefix announcements based on Regional Internet Registry (RIR) allocations or even Internet Routing Registry (IRR) objects, is conveying to the rest of the world, via the Border Gateway Protocol (BGP), that you, AS 17557 (PKTELECOM-AS-AP Pakistan Telecom), provide reachability for the internet address space (prefix) that actually belongs to YouTube, AS 36561," wrote McPherson. "YouTube [becomes] unavailable because all the BGP speaking routers on the internet believe Pakistan Telecom provides the best connectivity to YouTube."
The Pakistan Telecommunication Authority on Wednesday denied that it had caused the YouTube outage, insisting it had been caused by a "malfunction" elsewhere, the BBC reported.
"We are not hackers. Why would we do that?" Shahzada Alam Malik, head of the Pakistan Telecommunication Authority (PTA), told the AP news service.