Null Route
A networking technique that silently drops all traffic to a specific IP address.
A null route (also called a blackhole route) is when a network sends all traffic destined for a specific IP address to nowhere, effectively making that IP unreachable. Hosting providers sometimes null-route a customer's IP address during a DDoS attack to protect their network from the flood of traffic. While this stops the attack from affecting other customers, it also makes the targeted server completely unreachable until the null route is removed. This can cause Cloudflare error 523 (Origin Unreachable).