The Great Facebook Outage – October 4, 2021
“How a Routine Network Change Brought Down Facebook, WhatsApp & Instagram for 6 Hours”
Incident Overview
On October 4, 2021, billions of users around the world were abruptly cut off from their favorite social platforms — Facebook, WhatsApp, and Instagram — for more than six hours. The incident highlighted the vulnerabilities in large-scale, centralized infrastructures, and how even a minor configuration error can snowball into a global digital blackout.
Timeline of the Incident
|
Time (UTC) |
Event |
|---|---|
|
~15:30 UTC |
Network configuration change initiated by Facebook’s internal engineering team. |
|
~15:40 UTC |
Facebook’s DNS servers became unreachable; all domains began failing. |
|
16:00–18:00 UTC |
Facebook teams locked out of internal systems, including ID badges, internal dashboards, and tools. |
|
18:00–21:30 UTC |
Physical data center access initiated to manually restore BGP/DNS services. |
|
~21:45 UTC |
Gradual restoration of services begins. |
|
22:30 UTC |
Major services back online; full recovery over next few hours. |
What Went Wrong? (Technical Breakdown)
1. BGP Route Withdrawal
Facebook engineers issued a routine command intended to withdraw unused backbone routes from its Border Gateway Protocol (BGP) routers.
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BGP is the protocol that tells the internet how to reach specific IPs.
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The command accidentally removed all BGP routes to Facebook’s DNS servers.
2. DNS Servers Became Inaccessible
With no routes to Facebook’s DNS servers, any device trying to reach facebook.com, instagram.com, or whatsapp.com couldn't resolve their IPs — effectively making Facebook vanish from the internet.
3. Internal System Lockout
Since Facebook uses the same infrastructure for internal tools (login, remote access, communications), engineers couldn’t access systems remotely and had to physically go into data centers.
Incident Management Perspective
Detection
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External monitoring tools (like ThousandEyes, DownDetector) and social media flagged outages within minutes.
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Internal monitoring failed to escalate effectively due to the outage disabling internal alerting systems.
Initial Triage
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Facebook’s incident command team was formed but could not communicate through their internal messaging systems (Workplace).
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Engineers began using personal emails and alternative platforms (e.g., Zoom, Signal).
Investigation
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The outage was traced to missing BGP routes — a result of a recent configuration change.
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Confirmed by internal teams and third-party global internet monitors.
Mitigation & Recovery
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Facebook engineers were dispatched to physical data centers to manually reset configurations.
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Routes were reintroduced to BGP, DNS servers became accessible, and traffic was restored incrementally.
Closure
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A full Post-Incident Review (PIR) was conducted internally.
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The PIR emphasized the need for fail-safe access, out-of-band management, and segregated tooling for critical systems.
Business Impact
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Estimated Loss: ~$100M in ad revenue and business operations.
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Stock Price Dip: Nearly 5% drop in FB shares within 24 hours.
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Brand Trust: Millions of users lost faith in Facebook’s reliability.
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Employee Productivity: Internal tools were down; employee access was restricted.
Key Takeaways for IT Professionals
1. Redundancy in Monitoring
Implement third-party external monitoring to detect issues when internal tools go offline.
2. Out-of-Band Management
Maintain emergency remote access paths (e.g., VPN-less SSH, satellite phones) for critical configuration rollbacks.
3. Change Management Governance
Adopt stricter change approval workflows and real-time impact analysis before pushing config changes to production.
4. Documentation & Role Clarity
Ensure disaster recovery runbooks are accessible offline, and responsibilities are clear across the incident response team.
5. Communication Resilience
Use segregated, independent communication tools to coordinate during a company-wide internal outage.
Why It Matters
This wasn’t a cyberattack. It was a human error in a network update that cascaded due to the highly centralized nature of Facebook’s infrastructure. It proves that technical issues, when not accompanied by a well-practiced incident management process, can become business disasters.
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