anycast
termnetworkingcloud
One IP address announced from many locations, so users reach the nearest instance.
With anycast, the network's own routing sends each client to the closest advertising site, spreading load and shrinking latency, the backbone of modern DNS and CDNs. The same address, many places; the routing decides which one you get.
Anycast is the trick that makes global services feel local. The same address is advertised from many locations at once, and ordinary routing delivers each user to whichever instance is closest in network terms. No clever redirection is involved: the routing table is doing the work it always did, and the cleverness is in announcing the same destination from many places.
This is why it underpins the parts of the internet that must not fail. Root DNS servers, public resolvers, and CDN edges all use it, which is also why the popular claim that there are thirteen root servers is misleading: there are thirteen root server identities, served by well over a thousand physical instances worldwide. Taking down a root server address would require taking down all of them simultaneously.
The trade is that anycast suits short, self-contained exchanges better than long stateful sessions. If routing shifts mid-conversation, packets can arrive at a different instance with no knowledge of what came before. DNS queries tolerate this naturally; long-lived connections need extra care, which is why anycast tends to front the request rather than carry the whole session.
Also known as: any-cast