Anycast explained: one IP, servers everywhere

How does a service like a public DNS resolver answer in a few milliseconds whether you're in Paris, New York or Singapore, yet with a single IP address? The answer is one word: anycast. It's one of the most elegant techniques in Internet routing, and it's everywhere without being visible.

The principle: the same IP announced from several places

Normally an IP address maps to one machine in one place (that's unicast). With anycast, you announce the same prefix from multiple, geographically distributed sites. BGP routing then does its job naturally: each user is directed to the nearest instance in network terms (the shortest path). One IP, but dozens of points of presence.

Why it's powerful

• Lower latency: the user reaches the closest site, so the response is faster.
• Resilience: if a site goes down, BGP automatically reroutes traffic to the next one, with no address change.
• DDoS resistance: an attack is mechanically spread across the points of presence, instead of saturating a single site.
• Client simplicity: nothing to configure, a single address to know.

Where is anycast used?

Everywhere proximity matters. Public DNS resolvers and DNS root servers are the canonical example. CDNs rely on it to bring content closer. DDoS protection services use it to absorb and disperse attacks. Large SaaS platforms use it to offer global entry points.

What it takes to deploy

Anycast requires BGP expertise and several well-connected points of presence — that's where the operator comes in. A richly interconnected, multi-site network makes your anycast announcements effective. That's what our multi-site IP transit enables, natively DDoS-protected, with IPv4/IPv6 BGP sessions. Our managed IT can support you in designing an anycast architecture.