Published: March 27, 2026 In a previous post, we watched a single DNS misconfiguration on one AWS server bring 3,500 companies across 60 countries to a standstill. DNS lives at Layer 7. The failure started there. This kind of thing repeats. On June 21, 2022, a misconfigured BGP route at Cloudflare blocked 50% of all global HTTP traffic. No server was overloaded. No deployment had gone wrong. Packets simply lost their way and looped endlessly through the network. This time, the failure was at Layer 3. Both incidents share one thing: it took far too long to find the cause. Because no one knew which layer had failed. The OSI model is not a taxonomy for networking textbooks. It's a fault map — a way to pinpoint exactly where a system breaks. ref. Cloudflare Blog: Cloudflare outage on June 21, 2022 Why the Layers Don't Talk to Each Other Before the fault map makes sense, this question needs an answer. Why does the OSI model split into 7 layers at all?…