ANYCAST routing as the basis for every CDN - ­čĆć Managed Server


12 September 2023

ANYCAST routing as the basis for every CDN

What is ANYCAST routing and what are the advantages for creating a CDN?

Content delivery networks (CDNs) have become a cornerstone of modern web architecture. They allow you to distribute content to users spread across different parts of the world, optimizing performance and reducing latency. One of the most crucial aspects that allows a CDN to function effectively is ANYCAST routing. In this article, we'll take a detailed look at how ANYCAST routing works and why it's so critical to the operation of every CDN.

What is ANYCAST Routing?

ANYCAST is one of the IP routing methods used to address and route traffic in a network. Unlike the UNICAST and MULTICAST methods, ANYCAST allows you to route a single IP address to multiple destinations. When a packet is sent to an ANYCAST address, the router determines the most efficient route to reach one of multiple possible destinations.

Why is ANYCAST Important for CDNs?

What is Latency?

Before addressing ANYCAST's role in reducing latency, it is important to understand what latency itself is. In network terms, latency is the time it takes for a data packet to travel from one point to another in the network. This delay can be affected by various factors such as the physical distance between the client and the server, quality of network service, traffic congestion, and so on.

Why is it Important to Reduce Latency?

High latency can have a significant impact on user experience. For example, a slower loading time can make a website or application seem less responsive, thereby reducing user engagement and potentially increasing site abandonment rates. In the context of e-commerce applications, high latency can even lead to reduced conversions and a drop in revenue.

How ANYCAST Optimizes Latency in a CDN

ANYCAST routing addresses the latency issue in several ways:

Identification of the nearest PoP

When a user makes a request to a site that uses a CDN with ANYCAST support, the request is automatically routed to the PoP (Point of Presence) closest to the user. Each PoP is a physical location where the CDN servers are located. By having multiple PoPs in various geographic locations, ANYCAST can reduce the distance data has to travel, thus reducing latency.

Calculation of the Optimal Route

ANYCAST routing uses protocols such as Border Gateway Protocol (BGP) to calculate the most efficient route to route data. This not only reduces the distance the data has to travel, but also minimizes any delays caused by congestion or other network problems.

Dynamic Load Balancing

ANYCAST also allows for more sophisticated load balancing. If a PoP is particularly busy or experiencing a failure, ANYCAST can redirect requests to another PoP, ensuring latency remains minimal.

Practical Example

Imagine a user in Rome accessing a website hosted in a data center in the United States. Without a CDN, the user request would have to cross the ocean, leading to significant latency. However, if the site uses a CDN with ANYCAST support, the request could be routed to a closer PoP, perhaps located in Europe, drastically reducing latency.

Latency optimization is a key element to improving the performance and reliability of a CDN. Thanks to its ability to intelligently and dynamically route requests, ANYCAST routing is an essential component for any CDN that aspires to provide high-quality service. With the increasing adoption of complex web applications and the need to deliver content to a global user base, reducing latency through technologies like ANYCAST is more crucial than ever.

Technical Operation

Path Selection Algorithms

Routers use algorithms such as BGP (Border Gateway Protocol) to determine the shortest path to the desired destination. Such algorithms take into consideration various factors such as latency, number of hops and other metrics to select the optimal route.

Load Balancing

ANYCAST routing can be configured to load balance between different servers based on metrics such as server capacity, available bandwidth, and latency.

Practical Case: CDN and Web Performance Optimization

Let's imagine an e-commerce application that has a global user base and uses a CDN with ANYCAST support to deliver content. We examine three different scenarios, involving users from Italy, Brazil and Antarctica.

User in Italy

As already mentioned, a user accessing the application from Italy would be automatically routed to the nearest PoP, which could be located in Milan. The geographic proximity of the PoP would reduce latency to very low levels, perhaps less than 20 milliseconds, thereby improving the user experience. Web page and images would load quickly, making the entire browsing and purchasing process enjoyable and smooth.

User in Brazil

For a user in Brazil, the situation may be slightly different. Suppose the closest PoP is located in São Paulo. While latency would generally be higher than for a user in Italy (due to factors such as local network quality), it would still be significantly lower than directly accessing a server in the US or Europe. We could expect a latency of around 40-60 milliseconds, which is still acceptable for most web applications.

User in Antarctica

Antarctica represents a unique challenge. PoP availability in this region is almost non-existent due to logistical difficulties and high maintenance costs. In this case, the ANYCAST system could route traffic through a PoP in Australia or South Africa, depending on which route is more efficient. However, latency would inevitably be higher, perhaps reaching several hundred milliseconds.

In this situation, while the user experience would be compromised, it would still be better than what you would get without a CDN. Content optimization techniques, such as compression and caching, could be used to further mitigate the effect of high latency.

Challenges and Considerations

Implementing ANYCAST: The Need to Be an Autonomous System and Other Factors to Consider

Implementing ANYCAST is a task that requires some experience in networking and systems engineering, as well as some specific resources and technical requirements. One of the fundamental requirements for implementing ANYCAST is the need to be an Autonomous System (AS).

What is an Autonomous System?

An Autonomous System is a set of IP networks and routers that operate under a single routing policy and are under the control of a single administrative entity. An AS is identified by a unique number, known as an ASN (Autonomous System Number), which serves to distinguish the AS from other autonomous systems on the Internet. Being an AS is essential for implementing ANYCAST routing, as it allows the use of protocols such as the Border Gateway Protocol (BGP) to manage traffic routing efficiently.

autonomous system

Configuration Complexity

Setting up ANYCAST can be very complex and requires a good understanding of how networks work. The following are some of the technical considerations to take into account:

  1. BGP configuration: You need to configure BGP so that it can make intelligent decisions about traffic routing.
  2. PoP selection: The choice of Points of Presence (PoP) in various geographical locations is crucial for the performance of the network.
  3. Load Balancing: Load balancing strategies must be implemented to effectively distribute traffic across various PoPs.
  4. Failover management: In case of failure of a PoP or part of the network, it is necessary to have contingency plans to redirect traffic efficiently.

Associated Costs

  1. Cost of PoPs: Establishing multiple PoPs in various geographic locations can be costly in both hardware and network connectivity.
  2. Operating costs: Maintenance and management of an ANYCAST network requires specialized human resources, which can increase operational costs.
  3. License Fees: Some ANYCAST solutions may require the purchase of software licenses, further increasing costs.

However, the benefits generally outweigh the costs, providing a significant improvement in performance and redundancy. This is especially true for applications that require low latency and high availability, such as streaming services, e-commerce platforms and online games.


Implementing ANYCAST is not a task to be taken lightly, but the potential benefits in terms of performance and redundancy make the investment of time and resources very worthwhile. Being an Autonomous System is a key requirement to take full advantage of ANYCAST's capabilities, providing granular control over routing and enabling effective traffic management at a global level.

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