One address, many locations
With anycast, the same IP address is announced from multiple physical locations. The routing system naturally delivers each client to the nearest instance by network distance, without the client knowing there are many.
How it works
Multiple sites advertise the identical prefix into BGP. Routers along the way pick the closest origin, so packets converge on whichever site is fewest hops away.
- Many sites announce the same address.
- Routing steers each client to the nearest site.
- Withdrawing an announcement reroutes traffic to the next nearest.
Why it helps
Anycast lowers latency by serving from nearby and improves resilience, since a failed site simply stops announcing and traffic shifts elsewhere. It is the backbone of DNS root servers and large content networks. The catch is that stateful sessions can flip between sites if routing changes mid connection, so anycast suits stateless or short lived requests best.
Key idea
Anycast shares one address across many sites so routing delivers each client to the closest healthy one.