One Address, Many Sites
Anycast lets many physical servers in different locations share a single IP address. The network routes each query to whichever site is closest in routing terms, so the same address answers from many places at once.
How Routing Chooses
Anycast works at the routing layer. Each site announces the same address into the global routing system, and routers pick the shortest path.
- A client in one region reaches a nearby site automatically.
- No client configuration or DNS trick is needed; the address is the same everywhere.
- Adding a site simply means announcing the address from one more location.
Why DNS Loves It
Root and large recursive services use anycast heavily because DNS queries are small, stateless, and latency sensitive.
- Lower latency because the nearest site answers.
- Resilience because if one site fails, routing shifts queries to the next nearest.
- Capacity because traffic naturally spreads across sites by geography.
Since each DNS query is a self contained request, it does not matter that consecutive queries might land on different sites.
Key idea
Anycast announces one DNS address from many sites and lets routing send each query to the nearest one, giving low latency and automatic failover for stateless lookups.