Anycast IP Routing Explained: How Cloudflare & Google Announce One IP to the World

Unicast vs Anycast: The Architecture of Global Scale

In traditional Unicast Routing, a single IP address belongs to a single physical network interface card situated in one specific datacenter. If a user in Tokyo requests a server in Frankfurt, packets must cross the globe. In Anycast Routing, a single IP address (e.g., 1.1.1.1 or 8.8.8.8) is advertised simultaneously by hundreds of datacenters across the planet.

How BGP Anycast Routes Traffic to the Nearest Edge Node

Anycast functions through the internet core routing protocol, BGP (Border Gateway Protocol):

• Simultaneous BGP Route Announcements: Cloudflare or Google announces the same /24 IP prefix from over 300 edge datacenters worldwide to tier-1 transit providers (Telia, Lumen, NTT).
• Shortest AS-Path Routing: When an ISP router receives multiple announcements for the same IP, it routes user packets along the path with the fewest Autonomous System (AS) hops.
• Sub-10ms Latency: A user in São Paulo connects to an Anycast edge node in São Paulo, while a user in London connects to an edge node in London—both using the exact same destination IP.

The Ultimate DDoS Mitigation Weapon

Anycast is the primary foundation of modern DDoS defense. When a 1-terabit botnet attacks an Anycast IP, the malicious flood is naturally segmented and absorbed across 300 regional scrubbing centers rather than overwhelming a single origin server.

Learn more about global routing defense in our guide on Bogon IP filtering and BGP blackholing.

Test your connection latency and check your ISP routing on our free online IP check suite.