Understanding how Facebook disappeared from the Internet

On October 4th, 2021, at around 15:51 UTC, a major outage occurred affecting Facebook, WhatsApp, and Instagram. The issue began with a configuration change that affected the entire internal backbone of Facebook, causing its DNS names to stop resolving and infrastructure IPs to become unreachable. This led to the failure of Facebook's DNS, which in turn caused other networks worldwide to be unable to find Facebook's network, rendering it unavailable. The outage was eventually resolved by approximately 21:20 UTC when Facebook reconnected to the global Internet and DNS started working again.