Why did Facebook, Whatsapp, and Instagram went down (4/10/2021)

On Tuesday 5 pm UTC, people started reporting that they couldn't access Facebook, Instagram, Whatsapp, and messenger

Why did Facebook, Whatsapp, and Instagram Weren't working?

Official Facebook Report stated that

Our engineering teams have learned that configuration changes on the backbone routers that coordinate network traffic between our data centers caused issues that interrupted this communication. This disruption to network traffic had a cascading effect on the way our data centers communicate, bringing our services to a halt.

Our services are now back online and we’re actively working to fully return them to regular operations. We want to make clear at this time we believe the root cause of this outage was a faulty configuration change. We also have no evidence that user data was compromised as a result of this downtime.

This is what Cloudflare noticed

At 15:58 UTC we noticed that Facebook had stopped announcing the routes to their DNS prefixes. That meant that, at least, Facebook’s DNS servers were unavailable. Because of this Cloudflare’s 1.1.1.1 DNS resolver could no longer respond to queries asking for the IP address of facebook.com.

Meanwhile, other Facebook IP addresses remained routed but weren’t particularly useful since without DNS Facebook and related services were effectively unavailable:
We keep track of all the BGP updates and announcements we see in our global network. At our scale, the data we collect gives us a view of how the Internet is connected and where the traffic is meant to flow from and to everywhere on the planet.

A BGP UPDATE message informs a router of any changes you’ve made to a prefix advertisement or entirely withdraws the prefix. We can clearly see this in the number of updates we received from Facebook when checking our time-series BGP database. Normally this chart is fairly quiet: Facebook doesn’t make a lot of changes to its network minute to minute.

But at around 15:40 UTC we saw a peak of routing changes from Facebook. That’s when the trouble began.

This is a detailed analysis by the one and only MR. Hussein Nasser

Resources I used

Facebook Official Report
Understanding How Facebook Disappeared from the Internet by cloud flare
Hussein Nasser Youtube Channel