What Is Anycast?
Anycast is a network addressing method where multiple servers share the same IP address. Queries are routed to the nearest node based on BGP hop count, reducing latency and increasing resilience.
How It Differs from Unicast
Unicast binds one IP to one server; if that server fails, the domain goes offline. Anycast automatically reroutes traffic to the next closest node, often in <30 seconds, without DNS changes.
Inside the Architecture
- Identical zone files on every node
- BGP announcements from dozens of global PoPs
- Health checks withdraw failed nodes from route tables
- Resolver sees single IP, lowest RTT wins
Performance Benefits
Tests show 30-70% faster query resolution versus legacy single-server DNS. For e-commerce, a 100 ms speed gain can raise conversion 1-2%.
DDoS Mitigation
Because traffic disperses across nodes, a 500 Gbps attack is absorbed in smaller 5-10 Gbps chunks, each scrubbed locally. Anycast plus rate-limiting keeps authoritative DNS online during largest recorded attacks.
Setting Up Anycast
Most registrars offer it transparently (Cloudflare, NS1, Amazon Route 53). If you run BIND on own hardware, you need:
- Own IP prefix ≥/24 for IPv4, ≥/48 for IPv6
- ASN and BGP feeds at multiple IXPs
- Identical BIND config + rsync/git sync
- Out-of-band monitoring to withdraw bad routes
Limitations
Geolocation by IP becomes inaccurate—user in South Africa may exit via London node. Applications requiring precise geo should use EDNS Client Subnet or app-level GPS.
Cost Outlook
Cloud-based anycast DNS is free-$50/mo for millions of queries. Rolling your own requires $10k+ in routers, transit, and IP space—worthwhile only at registrar scale.
Key Takeaway
Anycast DNS is now the de-facto standard for speed and uptime. Unless you have regulatory reasons to keep DNS on-prem, outsource to anycast provider and gain global resilience overnight.