What Is Anycast? How Big Websites Stay Fast and DDoS-Resilient
Have you ever wondered why large public DNS resolvers and major CDNs load almost instantly for users all over the world? And why they stay online even under massive DDoS attacks?
One technology is central to the answer: Anycast.
Meanwhile, for many companies expanding overseas, the reality looks like this: a single server handles traffic from the whole world, distant users get slow load times, and one attack takes the entire site down. Let's look at how Anycast solves these problems.
Key Takeaways
- Anycast is a routing method in which the same IP address is announced from multiple nodes worldwide, and the BGP routing protocol sends each user to the node that is closest on the network.
- Anycast makes websites faster, more stable and more DDoS-resilient because users reach the nearest node, routes for a failed node are withdrawn automatically, and attack traffic is spread across many nodes.
- Building your own Anycast network typically requires your own ASN, an independently announceable IP block (for IPv4, usually at least a /24), server nodes in multiple regions, and data centers that support BGP sessions.
- Anycast is best suited to stateless or short-lived connection services such as DNS, CDNs, and global websites and APIs, while long-lived stateful workloads need supporting architecture such as session synchronization.
- IMIDC, a member of all four major RIRs (RIPE NCC, APNIC, ARIN and AFRINIC), provides ASN services, IP resources covering 24 regions, 9 data centers and BGP session support as a one-stop package for deploying Anycast.
1. What Is Anycast? The One-Sentence Answer
Anycast: the same IP address is announced from multiple locations around the world at the same time, and each user is routed to the node that is "closest" on the network.
An analogy: - Unicast: there is only one store in the country, and everyone has to travel to that one address. - Anycast: there is a chain of stores across the country, all with the same sign and the same name, and each customer automatically goes to the nearest one.
"Closest" here is determined by the BGP routing protocol based on network paths. It usually correlates with geographic distance, but the two are not exactly the same.
2. Anycast vs Unicast at a Glance
| Aspect | Unicast | Anycast |
|---|---|---|
| IP-to-node relationship | One IP maps to one node | One IP maps to multiple nodes |
| User access path | Everyone reaches the same location | Users connect to the nearest node |
| Speed for distant users | The farther away, the slower | Generally faster |
| Single point of failure | If the node fails, the service is unreachable | If one node fails, traffic automatically shifts to others |
| DDoS resilience | Attack traffic converges on one point | Attack traffic is spread across many nodes |
| Barrier to entry | Low | Requires an IP block and BGP capability, usually an ASN |
3. Why Is Anycast Both Fast and Resilient?
1. Fast: users automatically reach the nearest node
Users in Tokyo connect to the Japan node, users in Los Angeles connect to the US node, and users in Singapore connect to the Singapore node. Shorter physical distance and fewer network hops naturally mean lower latency.
2. Stable: automatic failover when a node goes down
When a node goes offline, its BGP announcement for the IP is withdrawn and traffic is routed to the other nodes. Users barely notice, and the service stays online.
3. Resilient: attack traffic gets "diluted"
A DDoS attack works by overwhelming the target with massive traffic. With Anycast, attack traffic coming from around the world is split across whichever nodes are closest to each source, so the load on any single node drops dramatically. This is one of the key reasons the DNS root server system makes wide use of Anycast.
4. Which Services Are a Good Fit for Anycast?
- DNS resolution: the classic Anycast use case.
- CDN and static content acceleration: delivering images, videos and downloads from the nearest location.
- Global websites and APIs: cross-border e-commerce, SaaS and open platforms.
- Game acceleration and login gateways: players connect to the nearest entry point.
- Entry layers that need high availability and attack resilience: such as gateways and reverse proxies.
Note: Anycast is best suited to stateless or short-lived connection services. For long-lived, stateful workloads, you need supporting architecture (such as session synchronization).
5. What Do You Need to Build Your Own Anycast Network?
To run your own Anycast network, you typically need:
- Your own ASN (Autonomous System Number): used to announce routes on the internet.
- An independently announceable IP block: for IPv4, usually at least a /24.
- Server nodes in multiple regions: all running the same service.
- Data centers that support BGP sessions: to establish BGP peering with upstream providers.
There are also a few details to get right: every node must serve consistent content; health checks must be configured so that route announcements are withdrawn promptly when a service fails, avoiding sending users to a node that is "alive but broken"; and routing policies must be coordinated with upstream carriers so traffic is distributed as intended. These tasks may seem minor, but they directly determine how well Anycast actually performs.
Sounds like a high bar? That is exactly where many businesses stop. IMIDC provides all of this as a one-stop service.
6. Why Deploy Anycast with IMIDC?
IMIDC (Rainbow Network) has provided network infrastructure services since 2014 and is a member of all four major RIRs: RIPE NCC, APNIC, ARIN and AFRINIC:
- ASN services: help with applying for and managing your own ASN.
- IP resources: IPs covering 24 regions, with multi-IP allocations of up to /24.
- BGP & Anycast support: data centers support BGP sessions and announcing your own IP blocks.
- 9 data centers: Hong Kong, Taiwan, Japan, South Korea, Singapore, Thailand, Russia, the United States and South Africa, a natural fit for multi-node deployment.
- CN2 direct connectivity + DDoS protection: Asian nodes balance access from mainland China with security.
- 10Gbps uplinks, all-SSD storage, Tier 3+ data centers, 99.9% uptime.
- 24/7 technical support: dedicated engineers help with BGP configuration and routing troubleshooting.
From ASN and IPs to servers and BGP sessions, you don't need to juggle multiple vendors. IMIDC covers it all.
FAQ
Is Anycast the same as a CDN?
No. Anycast is a routing method; a CDN is a content delivery service. Many CDNs use Anycast under the hood to route users to the nearest node, but some CDNs use DNS-based steering instead.
Can I use Anycast without my own ASN?
Some providers can announce your routes using their own ASN, but flexibility is limited. If you are planning a long-term global business, we recommend getting your own ASN and IP block so you control your routing.
Can Anycast fully stop DDoS attacks?
Anycast effectively spreads attack traffic and improves overall resilience, but it is not a cure-all. We recommend combining it with data center DDoS protection and scrubbing solutions.
What is the minimum number of nodes for Anycast?
Technically, two nodes are enough. But to get real acceleration and disaster-recovery benefits, cover the main regions where your users are located.
Conclusion: Give Your Website an Enterprise-Grade Architecture
Anycast is no longer reserved for tech giants. With the right ASN, IP and data center resources, small and mid-sized businesses can also build a network entry point that offers nearest-node access, automatic failover and DDoS resilience worldwide.
👉 Visit https://www.imidc.com and contact live support or submit a ticket. IMIDC network engineers will assess an Anycast deployment plan for you.