How Anycast works
With ordinary (unicast) addressing one address belongs to a single host. With anycast, dozens of servers around the world announce the very same address over the BGP protocol. When a request arrives, the network itself picks the shortest route and delivers the packet to the nearest instance. It works the same for IPv4 and IPv6, and if one location fails, traffic automatically shifts to the next.
Where it is used
Anycast is valued wherever speed and resilience matter:
- Root servers — DNS root servers use anycast so that DNS queries are served close to the user.
- CDN — a CDN delivers content from the nearest point of presence.
- DDoS protection — an attack is spread across many sites instead of one.
In effect, anycast provides natural load balancing at the routing level, without a separate load balancer.
