Definition
Anycast is an addressing and routing technique in which a single IP address is advertised from multiple physical locations at once. When a client connects to that address, the network's routing fabric delivers the packets to whichever instance is closest in routing terms, not to one fixed machine. This is the opposite of unicast, where one address maps to exactly one server and all traffic always lands there. The result is that the same service IP can be served by dozens of geographically dispersed nodes while users transparently hit the nearest one.
How BGP makes anycast work
Anycast is built on top of BGP. Each location announces the identical prefix to its upstream networks, and BGP's best-path selection naturally steers each requester toward the announcement with the lowest-cost route, factoring in hop count, transit cost, and latency. If one node fails or stops announcing the prefix, routes simply converge onto the remaining instances, giving automatic failover without any client-side changes or DNS reconfiguration.
Where it is used
Anycast underpins the most resilience-critical parts of the internet: root and recursive DNS resolvers, public DNS services, and large-scale DDoS absorption all rely on it to spread load and stay reachable under attack. For a sovereignty-minded operator, anycast is how you turn several independent points of presence into one robust, location-aware service. It pairs naturally with a load balancer at each site, where anycast picks the nearest region and the local balancer distributes traffic across the servers inside it.
In Simple Terms
Anycast is an addressing and routing technique in which a single IP address is advertised from multiple physical locations at once. When a client connects…