Anycast DNS is a network addressing and routing methodology where multiple physical servers share a single IP address across different geographical locations. Unlike Unicast routing, which maps an IP to a single interface, Anycast directs incoming queries to the topologically closest node from the requester's perspective.
How it works
The system relies on the Border Gateway Protocol (BGP) to announce the same IP prefix from multiple locations. Internet routers calculate the shortest path to the destination based on network metrics. If a specific node fails or experiences congestion, BGP automatically reroutes traffic to the next nearest available server, providing seamless failover and redundancy.
This architecture is primarily used for:
- Reducing latency by processing requests at the network edge;
- Distributing global traffic load across multiple data centers;
- Mitigating DDoS attacks by isolating high-volume traffic within specific geographical segments.
A practical example is the deployment of Root DNS servers and public resolvers. By using Anycast, services like 1.1.1.1 achieve global response times under 50ms, as the request is handled by a local point of presence (PoP) rather than traveling across oceans to a central server.