Anycast explained: Advantages and drawbacks

Anycast explained: Advantages and Drawbacks

IPv4 and IPv6 addresses have three common types: Unicast, Multicast, and Broadcast. Anycast is not a type of address in the same sense as Unicast, Multicast, and Broadcast; rather, it’s a routing methodology that can be applied to both IPv4 and IPv6 addresses. In this piece, we’ll delve into the functionality of Anycast and its significance, as well as shed light on certain limitations..

How does Anycast work?

We’ve previously mentioned about Anycast IP. But, let’s just go over the basics again, just to refresh our memories.

Anycast refers to the network configuration where multiple servers or nodes share the same IP address. In a normal network, each connected machine must have a different IP address from the others.

However, the magic is done via the Border Gateway Protocol on the routers. When trying to send data to an Anycast IP, the router will route the data to the nearest healthy server or the most appropriate server.

The network routing can be determined by network latency, routing configuration or geographical proximity. Servers using Anycast IP are usually located far from each other to provide a form of geographical load balancing.

Why use Anycast?

Organizations running critical network services such as Domain Name Service (DNS) servers or Content Delivery Network (CDN) servers are the most commons users of Anycast. Without DNS servers, we would be surfing websites using only IP addresses as opposed to using a friendly domain name like The DNS server translates the user-friendly name into its corresponding IP address to enable data transmission to the server. Meanwhile, CDN servers are located around the world to serve as localized website caches for frequently requested items such as images, JavaScript codes and videos.

With Anycast, network services are able to serve a huge number of requests simultaneously from around the globe due to its geographical load balancing feature. E.g., Website users from the United States and Canada will be routed to the servers situated in North America while users from South East Asia may be served by servers in Singapore.

In addition, it can help to absorb the devastating flood of requests from Distributed Denial of Service (DDoS) attacks. Just by having many servers dispersed throughout the world, DDoS attacks are mitigated by the sheer fact that attacks from various regions are diverted to their respective regional servers. Any network service using Anycast will remain accessible and be highly resilient to DDoS attacks by sharing the load among hundreds or thousands of servers.

High traffic websites like e-commerce sites or search engines frequently use Anycast IP as they must maintain a reasonable response time when serving user requests. By having the nearest server attend to the user’s request, the lower network latency and faster response will definitely give a better impression to the end user.

Another great feature of using an Anycast network is to have an automatic failover to the next nearest healthy server. No critical online services can afford any downtime, therefore having the Anycast network providing fault tolerance is a welcome feature indeed.

Drawbacks of Anycast

To implement your own Anycast network, there are a lot of effort and costs involved. Additional hardware and routing need to be setup and configured. Then, there’s the cost of procuring servers in the various data centers around the world.

There is also a need to setup the “heartbeat” monitoring service that will check the health of every server in the network to make sure they are responding to requests. Unhealthy ones will need to be excluded from the routing automatically.

Diagnosing the connectivity issues is also complicated due to the automated routing and requires analyzing data from logs, monitoring service, BGP metrics and much more.

Trying to determine the IP geolocation of any Anycast IP is pointless as it will show a different geolocation based on the location of the users. The IP2Location DB25 data contains the address_type field which can show if an IP is Anycast. If the type is Anycast, then be aware that the geolocation data contained within may not be accurate.


There is no denying the benefits that using Anycast IP for critical online systems can bring. Benefits such as faster response times to the lower network latency when transmitting or receiving data. Coupled with the geographical load balancing feature intrinsic to Anycast networks, organizations and businesses can keep operating at peak efficiency, even during a DDoS attack.


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