Diluting the Attack
Anycast is one of the most effective architectural defenses against DDoS (Distributed Denial of Service) attacks. A DDoS attack works by overwhelming a target with more traffic than its network connection or servers can handle. Anycast defeats this by making it structurally impossible to concentrate the attack.
Unicast scenario:
An attacker controls a botnet that generates 500 Gbps of traffic aimed at your server's IP in Virginia. Your datacenter uplink is 100 Gbps. Your server goes offline in seconds. Every user on Earth is affected.
Anycast scenario:
The same 500 Gbps attack targets your Anycast IP. But the attack traffic originates from bots distributed globally — some in Europe, some in Asia, some in the Americas. BGP routes each bot's traffic to the nearest Anycast POP:
- European bots → Frankfurt (receives ~150 Gbps)
- Asian bots → Singapore (receives ~120 Gbps)
- American bots → New York (receives ~230 Gbps)
If each POP has 300 Gbps of capacity and scrubbing infrastructure, all three sites absorb the attack. No single site is overwhelmed. Legitimate users in each region continue to be served normally, because their traffic also routes to their local POP — which is handling the attack traffic on a separate scrubbing pipeline.
This is exactly how Cloudflare absorbed a 3.8 Tbps DDoS attack in 2024 — the largest ever recorded at the time. Their Anycast network spread the load across hundreds of POPs, each absorbing a fraction of the total volume.