Facebook suffered significant downtime on Monday 4th October, taking around six hours to become available again. Its sister services Messenger, WhatsApp and Instagram also suffered complete outages, with billions of users around the globe unable to access the messaging platforms. Users first noticed that they could not access Facebook at around 5 pm UTC. It soon became apparent that “backbone routing settings” were the cause of the downtime, and Facebook engineers pinpointed an issue with Domain Name System (DNS) and Border Gateway Patrol (BGP) in particular. It was revealed that Facebook updates caused problems with BGP settings, and consequently, Facebook’s servers were unreachable until fixed.