Anycast

How Anycast Works

Anycast routing works by advertising the same IPv4Internet Protocol version 4. The fourth revision of IP using 32-bit addresses (e.g., 192.168.1.1), providing approximately 4.3 billion unique addresses. Still the most widely used internet protocol despite address exhaustion. or IPv6Internet Protocol version 6. The successor to IPv4 using 128-bit addresses (e.g., 2001:0db8::1), providing a virtually unlimited address space of 3.4 x 10^38 addresses. Designed to solve IPv4 address exhaustion. prefix from multiple physical locations simultaneously. When a client sends a packet to an anycast address, the internet's routing infrastructure — specifically BGP — automatically delivers it to the topologically nearest node announcing that prefix. "Nearest" is determined by AS path length and other routing metrics, not necessarily geographic distance.

Unlike UnicastA network communication method that sends data from one sender to one specific receiver. The most common form of IP communication, used for web browsing, email, and file transfers., where a single host owns an address, anycast distributes that ownership across a fleet of servers. If one node goes offline, BGP reconverges and traffic shifts to the next-best node within seconds, providing automatic failover without any client-side changes.

Common Use Cases

Anycast is foundational to the modern internet. The DNS root servers (operated by organizations like ICANN and Verisign) each serve a single anycast address, yet are physically replicated hundreds of times worldwide. Content delivery networks use anycast to route users to their nearest PoP. DDoS mitigation providers absorb attack traffic by spreading it across global anycast nodes so no single location is overwhelmed.

Anycast vs. Other Addressing Methods

Use DNS Lookup to see how anycast DNS resolves differently from different regions.