The events
On 24th Feb, 2008, the whole world became unable to reach YouTube
(AS36561). What happened, is that Pakistan Telecom
(AS17557), who had decided to blacklist YouTube, started
announcing one of their prefixes, but in a more specific way (i.e. announcing a
/24 within a /20). This would have ended-up armlessly if PCCW
(AS3491), on of their upstreams, hadn't re-announced this
prefix to all of their peers (PCCW is a pretty big carrier, with quite a few
transit customers...). This /24 range contained YouTube's DNS, so that Pakistan
Telecom have been blackholing YouTube for about one hour.