Unicast vs Anycast: the core difference
In standard Unicast routing, each server has a unique IP address. If a user in Jakarta queries a DNS server hosted only in New York, every query must travel halfway around the world — adding 200–300ms of latency.
In Anycast routing, multiple servers in different locations all advertise the same IP address via BGP (Border Gateway Protocol). The internet's routing infrastructure automatically selects the "closest" server based on network topology — typically the one with the fewest BGP hops or lowest measured latency.
The client doesn't know which server answered. From its perspective, it queried an IP address and got a fast answer. The geographic distribution is invisible at the application layer.
How Anycast DNS improves TLD performance
Anycast can help TLD operators in three ways:
Reach and latency
Multiple service locations give queries a choice of closer routes. Actual latency still depends on routing, connectivity, and user location.
Resilience during an outage
When a location becomes unreachable, routing changes can shift traffic to a healthy site. Recovery speed depends on detection, BGP configuration, and network conditions.
DDoS mitigation
Attack traffic can spread across sites, but distribution is not necessarily even. Backbone capacity does not guarantee the same capacity for every client. ADG offers up to 1 Tbps of backbone-level mitigation capacity, with per-client limits defined by configuration and agreement.
Anycast DNS for ICANN-compliant TLD operations
A TLD's Registry Agreement and technical specifications define availability, diversity, and recovery obligations. The exact requirement depends on the applicable agreement and service scope.
Anycast is a widely used way to improve resilience and reach: the same DNS service is announced from multiple locations, so queries can be routed to a healthy nearby site. ADG offers access to 30+ Anycast nodes across six continents through the .id Registry global infrastructure. The applicable availability target, coverage, recovery objective, and capacity are documented in the service agreement.
Anycast vs GeoDNS: what's different?
Anycast and GeoDNS are sometimes confused. They solve similar problems differently:
| Anycast DNS | GeoDNS | |
|---|---|---|
| Routing mechanism | BGP network routing | Application-layer logic |
| Awareness | Network topology (hops) | Geographic IP databases |
| Failover speed | Seconds (BGP reconvergence) | Depends on TTL + health check |
| DDoS protection | Inherent (traffic distributed) | Minimal |
| Use case | Authoritative nameservers | Load-balancing HTTP responses |
For authoritative DNS nameservers — the servers that TLD operators run — Anycast is the correct technology. GeoDNS is more commonly used for balancing traffic among application servers (web, API).
Frequently asked questions
How many Anycast nodes do I need for 99.999% uptime?
There is no universal node count that guarantees a 99.999% target. Availability also depends on provider diversity, routing, monitoring, failover, change control, and operations. ADG can map the required target to a proposed topology and document the commitment in the service agreement.
Can I run Anycast DNS myself instead of using an RSP?
Technically yes, but operationally challenging. Running Anycast DNS requires BGP peering agreements with ISPs, co-location agreements in multiple datacenters globally, 24/7 NOC coverage, DNSSEC infrastructure, and expertise in RFC-compliant TLD operations. Most TLD operators choose an RSP to avoid this operational complexity.
Does ADG's Anycast network support IPv6?
Yes. ADG's Anycast DNS network is fully dual-stack, supporting both IPv4 and IPv6. ICANN requires TLD operators to support IPv6 for both their DNS nameservers and WHOIS/RDAP endpoints.