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Reliable DNS: What Is Anycast DNS?

March 17, 2023 | By David Selden-Treiman | Filed in: DNS.


Anycast DNS is a networking technique that routes DNS queries to the geographically nearest server from multiple servers sharing the same IP address. This provides improved performance, reduced latency, and increased resilience.


Anycast DNS is an advanced method of distributing DNS queries across multiple servers located in different geographical locations. This technique is particularly beneficial as it enables DNS queries to be directed to the nearest available server, minimizing latency and ensuring a faster response time.

As opposed to the traditional Unicast DNS, which directs queries to a single DNS server, Anycast DNS offers a more efficient and robust solution for handling DNS traffic, making it an attractive choice for today’s internet infrastructure. Anycast DNS helps ensure fast, efficient DNS lookups.

What are the Types of DNS Servers?

As you explore the world of the DNS server types, it’s essential to understand the differences between Unicast DNS and Anycast DNS.

Unicast DNS

Unicast DNS is the conventional method of handling DNS queries. Each DNS server has a unique IP address.

Queries are directed to a specific server, which can sometimes be far away from the user, resulting in increased latency and slower response times. Furthermore, Unicast DNS can experience performance issues if the server becomes overloaded or suffers from an outage.

Anycast DNS

On the other hand, Anycast DNS provides a more advanced approach to handling DNS queries. In this method, multiple DNS servers share a single IP address, and each server is strategically located in various geographical locations.

The key features of Anycast DNS include:

  • efficient routing of DNS queries,
  • automatic load balancing, and
  • network redundancy.

As a result, Anycast DNS helps ensure that DNS queries are directed to the nearest available server, leading to lower latency, improved performance, and greater resilience against network failures and attacks.

How Does Anycast DNS Work?

To fully grasp how Anycast DNS works, it’s important to understand the concept of Anycast IP addressing.

Unlike Unicast IP addressing, where each server has a unique IP address, Anycast IP addressing involves multiple servers sharing the same IP address. This enables the routing and selection process to function more efficiently through the use of the Border Gateway Protocol (BGP).

BGP is responsible for directing the DNS query to the nearest Anycast DNS server, based on factors such as network proximity and server load.

Anycast DNS also offers network redundancy and load balancing, which are essential for maintaining a reliable and resilient DNS infrastructure. The distributed nature of Anycast DNS servers allows for the automatic distribution of DNS queries among different servers, preventing any single server from becoming overloaded.

In case of a server failure or outage, the Anycast DNS system will automatically redirect the queries to the next nearest available server. This ensures minimal disruption to end users.

This built-in redundancy and load balancing make Anycast DNS a highly reliable solution for managing DNS traffic.

Why Is Anycast DNS Better?

Improved Performance

When considering the benefits of Anycast DNS, improved performance stands out as a significant advantage. By directing DNS queries to the nearest available server, Anycast DNS minimizes latency and ensures faster DNS resolution. This results in a better browsing experience for users and reduced load times for websites and applications.

Enhanced Security

Enhanced security is another key benefit of Anycast DNS. The distributed nature of Anycast DNS servers makes it more difficult for attackers to target a specific server, helping to mitigate Distributed Denial of Service (DDoS) attacks.

Furthermore, Anycast DNS is highly resilient against server outages, as the system can automatically reroute queries to another server if one fails or experiences issues.


Scalability is yet another important advantage of Anycast DNS. As your network expands, you can easily add more Anycast nodes to handle increased traffic and maintain optimal performance. This flexible approach ensures that your DNS infrastructure can adapt to growing demands without the need for significant overhauls or reconfigurations. Overall, Anycast DNS offers a robust and versatile solution for managing DNS traffic, catering to the evolving needs of modern internet infrastructure.

Implementing Anycast

Implementing Anycast DNS involves setting up multiple DNS servers that share the same IP address and are distributed across various geographical locations.

To ensure optimal performance and reliability, it’s essential to adhere to best practices when deploying Anycast DNS servers. These include selecting appropriate server locations to cover the target audience, ensuring sufficient network capacity, and maintaining a robust and secure network infrastructure.

When configuring Anycast DNS services, you can choose from various DNS service providers or set up your custom solution using popular DNS software like BIND (Berkeley Internet Name Domain). To implement Anycast DNS using BIND, follow these steps:

  1. Install BIND on multiple servers: Install the BIND software on all the servers that you want to include in your Anycast DNS network. Ensure that each server has sufficient resources to handle the expected DNS query load.
  2. Configure the named.conf file: On each server, configure the named.conf file with the required settings, such as the shared Anycast IP address, zone files, and any specific security settings. Make sure that the configuration is consistent across all servers.
  3. Set up BGP routing: Configure your network routers to use the Border Gateway Protocol (BGP) and advertise the shared Anycast IP address from each server. This will enable the routing infrastructure to direct DNS queries to the nearest server based on network proximity.
  4. Synchronize zone files: To ensure consistency across all Anycast DNS servers, regularly synchronize the DNS zone files using a tool like rsync or a version control system like Git. This will help maintain the integrity of the DNS data and prevent inconsistencies that may lead to errors or downtime.
  5. Monitor and troubleshoot: Regularly monitor your Anycast DNS network for performance, security, and stability. Use tools like dig, nslookup, or traceroute to troubleshoot issues and ensure that DNS queries are being correctly routed to the nearest server.

By following these steps and maintaining a consistent configuration across your Anycast DNS servers, you can successfully deploy an Anycast DNS network using BIND. This will enable you to take full advantage of the performance, security, and scalability benefits that Anycast DNS has to offer.

What Is the Border Gateway Protocol?

BGP is a path vector protocol, which means that routers using BGP maintain a table of routes, along with the path information necessary to reach a specific network. This enables BGP routers to make informed decisions about the best path to forward packets to their destination. BGP routers establish connections, or “sessions,” with their neighbors and exchange routing information, including the list of available routes and their associated path attributes.

One of the key features of BGP is its ability to choose the best route based on various factors, such as the number of AS hops, the shortest path, or other policy-based criteria. This flexibility allows network administrators to implement complex routing policies and optimize network performance. BGP also provides loop prevention by including the AS path in its updates, which allows routers to detect and discard routes that would cause loops.

BGP plays a critical role in Anycast DNS, as it directs DNS queries to the nearest available server based on network proximity. By utilizing BGP, Anycast DNS can efficiently route queries, minimize latency, and offer improved performance.

How Do I Set Up the Border Gateway Protocol for Anycast DNS?

Setting up a server with the Border Gateway Protocol (BGP) to use with Anycast DNS involves several steps, which require a good understanding of networking concepts and familiarity with configuring routers and servers. Follow these steps to set up a BGP-enabled server for Anycast DNS:

Acquire An Autonomous System Number (ASN)

To set up a BGP-enabled server, you will need an Autonomous System Number (ASN) for your network. This unique identifier is essential for BGP routing and can be obtained from your regional Internet registry (RIR), such as ARIN, RIPE NCC, or APNIC.

Obtain An IP Address Space

To establish your Anycast DNS network, you’ll need a block of IP addresses. You can either use provider-independent IP addresses, which can be obtained from your RIR, or provider-assigned IP addresses from your Internet Service Provider (ISP).

Set Up Your DNS Servers

Install and configure the DNS software, such as BIND, on multiple servers that will be part of your Anycast DNS network. Ensure that each server has the same configuration, including the shared Anycast IP address for your DNS service.

Configure BGP on Your Routers

To enable BGP routing, you’ll need to configure your routers to support BGP and establish BGP sessions with your neighboring ASes. This typically involves specifying your ASN, configuring BGP neighbor relationships, and defining routing policies.

Advertise your Anycast IP address

Using BGP, advertise the shared Anycast IP address from each of your DNS servers. This will enable the global routing infrastructure to direct DNS queries to the nearest server based on network proximity.

Test Your Anycast DNS Network

Verify that your Anycast DNS network is functioning correctly by using diagnostic tools like dig, nslookup, or traceroute. Ensure that DNS queries are being correctly routed to the nearest server and that your BGP routing policies are working as intended.

What Software is Used to Handle BGP Routing?

There are several software solutions available to handle BGP routing, each with its own set of features and capabilities. Some popular BGP routing software options include:


Quagga is an open-source routing software suite that provides implementations of various routing protocols, including BGP, OSPF, and RIP. Quagga is widely used for its flexibility, ease of configuration, and strong community support.

BIRD (BGP Internet Routing Daemon)

BIRD is another open-source routing software that supports BGP, OSPF, RIP, and other routing protocols. It is known for its performance, stability, and efficient memory usage. BIRD is commonly used by Internet Service Providers (ISPs) and internet exchange points (IXPs).

FRRouting (FRR)

FRRouting is a free, open-source routing software suite that evolved from Quagga. FRR supports multiple routing protocols, including BGP, OSPF, and RIP. It offers improved performance, stability, and a more active development community compared to Quagga.

What Are The Limitations of Anycast DNS?

Possible Routing Inefficiencies

While Anycast DNS offers numerous benefits, it’s important to be aware of some limitations and considerations before implementing this technology. One potential issue is routing inefficiencies that may arise due to the dynamic nature of the internet’s routing infrastructure.

Although BGP does a commendable job of directing queries to the nearest server, there may be instances where suboptimal routing occurs. This can result in longer response times or increased latency, which can impact the overall performance of your Anycast DNS network.

Monitoring & Troubleshooting

Anycast DNS can also pose challenges, as it can be difficult to determine which server is handling a specific DNS query. Traditional diagnostic tools, like ping and traceroute, may not provide accurate results due to the nature of Anycast routing. To overcome these challenges, you may need to invest in specialized monitoring tools and adopt tailored troubleshooting strategies that consider the unique aspects of Anycast DNS.

It’s More Expensive

Lastly, cost implications should be considered when deploying Anycast DNS. Setting up and maintaining multiple servers in various geographical locations can be more expensive than running a Unicast DNS infrastructure. Also, if you have to pay for a block of IPv4 addresses, that too can be an issue.

However, it’s crucial to weigh these costs against the benefits of improved performance, security, and reliability that Anycast DNS can provide for your network.


In conclusion, Anycast DNS presents a powerful and efficient solution for managing DNS traffic in today’s ever-evolving internet landscape. By intelligently directing queries to the nearest available server, Anycast DNS offers improved performance, lower latency, and faster DNS resolution for end users. The distributed nature of Anycast DNS servers also enhances security by making it more difficult for attackers to target a specific server, and provides resilience against server outages and failures.

As you weigh the benefits of Anycast DNS against its limitations, it’s important to consider the specific needs and requirements of your network infrastructure. By doing so, you can ensure that you make the most of this advanced technology and contribute to a more stable, secure, and efficient internet experience for users worldwide.

As the internet continues to grow and evolve, Anycast DNS is poised to play an increasingly important role in maintaining optimal performance and reliability. Stay informed about the latest developments and trends in Anycast DNS technology to ensure that your network remains up-to-date and ready to meet the challenges of the modern internet landscape.

David Selden-Treiman, Director of Operations at Potent Pages.

David Selden-Treiman is Director of Operations and a project manager at Potent Pages. He specializes in custom web crawler development, website optimization, server management, web application development, and custom programming. Working at Potent Pages since 2012 and programming since 2003, David has extensive expertise solving problems using programming for dozens of clients. He also has extensive experience managing and optimizing servers, managing dozens of servers for both Potent Pages and other clients.


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