As most people will already know, Facebook, Instagram, WhatsAPP and Oculus VR went down early on October 4, 2021, and the outage continued through the afternoon. It's been determined from multiple sources that the outage is likely due to a major misconfiguration that knocked the sites completely off the Internet in what has been described as an epic and nightmare scenario.
Earlier on Monday, Facebook began slowing down and completely stopped, with browsers unable to resolve the domain. The problem happened across other Facebook owned sites as well. The configuration errors that caused Facebook to go offline appear to have done more than just take it offline, it essentially made Facebook disappear from the Internet.
It turns out the problem may have been due to the configuration of Facebook's Border Gateway Protocol (BGP) routing. The BGP routing protocol is a service that calculates the most efficient path to reach a website through the multiple autonomous systems/networks that form the Internet.
Basically, when a browser asks for Facebook.com the domain name is translated by the DNS system to an Internet Protocol address (IP address) to a series of numbers that is an address. That IP address number is the address of the content on Facebook's servers. The browser makes the request and the BGP routing system calculates the fastest series of network hops to reach that content on Facebook's servers.
According to reports on Twitter, the BGP routes to Facebook have been dropped from the Internet. The CTO of Cloudflare tweeted that five minutes before the Facebook DNS stopped working, they noticed a large number of BGP route withdrawals. Cyber Security Expert Kevin Beaumont called it an "epic configuration error."