Anycast is a routing method where the same IP address is announced from many servers in different locations. The internet's routing system sends each visitor to the nearest (in network terms) server. Anycast DNS uses this to make nameservers fast worldwide and hard to knock offline. This guide explains how it works.
Before you start
No setup is needed – this is a concept guide. Anycast is usually something you get from a DNS or CDN provider rather than build yourself.
Unicast vs anycast
| Unicast | Anycast | |
|---|---|---|
| IP address | One IP = one server | One IP = many servers |
| Routing | Every visitor reaches the same machine | Each visitor reaches the nearest node |
| Latency | Depends on distance to that server | Low for most of the world |
| Single-site failure | Service down | Traffic moves to other nodes |
How anycast works
- A provider runs DNS servers in many data centres, each configured with the same IP address.
- Each site announces that IP prefix to the internet with BGP.
- Routers choose the shortest BGP path, so a resolver in Frankfurt reaches the Frankfurt node and one in Singapore reaches the Singapore node.
- If a node fails or is withdrawn, its announcement disappears and traffic flows to the next-nearest node.
DNS suits anycast well because most queries are a single UDP packet and response, so changing routes mid-session rarely matters.
Benefits of anycast DNS
- Speed – lower lookup latency for global visitors.
- Resilience – a data-centre outage does not take DNS down.
- DDoS absorption – attack traffic is spread across many sites instead of hitting one.
- Simplicity for users – the same nameserver IPs work everywhere.
The DNS root servers and big public resolvers such as 1.1.1.1 and 8.8.8.8 all use anycast.
Limits of anycast
- "Nearest" means shortest BGP path, which is not always lowest latency.
- Running your own requires your own IP prefix (at least a /24 for IPv4), an ASN and BGP sessions in every location.
- Long TCP connections can break if routing changes mid-connection, which is why anycast is more common for DNS and CDNs than for application servers.
Do you need anycast DNS?
- For a typical site whose visitors are mostly in one region, two or more well-run unicast nameservers are fine.
- For global audiences, high traffic or DDoS-prone sites, use a DNS provider with an anycast network, or a CDN such as Cloudflare in front of your hosting.
Check whether a nameserver uses anycast
- Run
tracerouteormtrto the nameserver IP from different locations – the final hop will be in different cities. - Some providers answer
dig @ns.example CH TXT id.serverwith the node name, showing which site you reached.
FAQ: anycast DNS
Is anycast the same as load balancing?
It spreads traffic by geography and routing, not by server load. Many providers combine both.
Does anycast DNS make my website faster?
It speeds up the DNS lookup, which is the first step of every new visit. Page speed after that depends on your hosting and caching.
Can I use anycast DNS with cPanel hosting?
Yes, by pointing your domain's nameservers to an anycast DNS provider and keeping A records pointed at your hosting server.