2021 Facebook outage

On October 4, 2021, at 15:39 UTC, the social network Facebook and its subsidiaries, Messenger, Instagram, WhatsApp, Mapillary, and Oculus, became globally unavailable for a period of six to seven hours. The outage also prevented anyone trying to use "Log in with Facebook" from accessing third-party sites. During the outage, many users flocked to Twitter, Discord, Signal, and Telegram, resulting in disruptions on these sites' servers. The outage was caused by the loss of IP routes to the Facebook Domain Name System (DNS) servers, which were all self-hosted at the time. Border Gateway Protocol (BGP) routing was restored for the affected prefixes at about 21:50, and DNS services began to be available again at 22:05 UTC, with application-layer services gradually restored to Facebook, Instagram, and WhatsApp over the following hour, with service generally restored for users by 22:50.

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