The old network troubleshooting saying is, when anything goes wrong, "It's DNS." This time Domain Name Server (DNS)[1] appears to be the symptom of the root cause of the Facebook global failure.[2] The true cause is that there are no working Border Gateway Protocol (BGP)[3] routes into Facebook's sites.
BGP is the standardized exterior gateway protocol used to exchange routing and reachability information between the internet top-level autonomous systems (AS)[4]. Most people, indeed most network administrators, never need to deal with BGP.
Many people spotted that Facebook was no longer listed on DNS[5]. Indeed, there were joke posts offering to sell you the Facebook.com domain[6].
Cloudflare[7] VP Dane Knecht was the first to report the underlying BGP problem[8]. This meant, as Kevin Beaumont, former Microsoft's Head of Security Operations Centre, tweeted, "By not having BGP announcements for your DNS name servers, DNS falls apart[9] = nobody can find you on the internet. Same with WhatsApp btw. Facebook have basically deplatformed themselves from their own platform."
Whoops.
As annoying as this is to you, it may be even more annoying to Facebook employees. There are reports that Facebook employees can't enter their buildings[10] because their "smart" badges and doors were also disabled by this network failure. If true, Facebook's people literally can't enter the building to fix things.
In the meantime, Reddit[11] user u/ramenporn, who claimed to be a Facebook employee working on bringing the social network back from the dead, reported, before he deleted his account and his messages, that "DNS for FB services has been affected[12] and this is