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.