What is CDN? How does it work?

A Content Delivery Network or a Content Distribution Network (CDN) is a distributed system of servers, strategically deployed in multiple data centers across the globe. Within a CDN, your content is available in many copies throughout these servers. In other words, a CDN is an interconnected system that caches, stores, and distributes your content to many end-users simultaneously. The ultimate goal of this technology is to deliver content to thousands of end-users with high availability and high performance.

For instance, without CDN, if your website is based in Los Angeles, the people who are accessing it from San Francisco will receive the content faster than people accessing it from Shanghai. The farther away the person accessing the website or application is, the longer the load time and the more frustrating the user experience becomes. In case of CDN usage, each end-user will access the same content from the closest CDN server and there will not be a significant performance difference between the end-users based on their location.

How Do CDNs Work?

CDNs are made up of a network of servers referred to as “Points of Presence” or PoPs. Each one of these servers (PoPs) is expanded in locations all over the world. The CDN server located closest to the end-user is called as “Edge Server.” When a user requests content from a website or application through a CDN, they will be connected to the closest edge server. This ensures the user will receive the best performance experience possible.

Why should we use CDN?

Faster Performance and Lower Latency

The very first reason to use a CDN is to provide an easy way to increase the speed of your websites while lowering the latency simultaneously.

Traditional Web Hosts Can’t Keep Up

Traditional web hosting is no longer capable of meeting the demands of websites. A CDN, made up of edge servers that are deployed in different locations of the world, now play a significant role in surpassing the computing resources of traditional web hosting in order to deliver rich and high-quality multimedia content in a reliable and cost-effective way. CDNs now are responsible for a majority of the load on a lot of websites. This can allow for savings on your web host and also less of your resources being used.

SEO Advantages

When it comes to search engine optimization (SEO) page speed is a very important factor as it pertains to page rankings. Most search engines consider the page loading time in their formulas.


Some websites may go down at one point, which can be very frustrating. It may also lead to a loss of income in the case of e-businesses.  However, due to CDNs’ architecture, CDNs improve reliability for your service. With a CDN, requests for specific content are always routed to the nearest and most available PoP. In case of any failure in a PoP, the next most available PoP will take over the request and send the requested content.

Traffic Spikes & Scalability

With the majority of resources now being delivered via a content distribution network, your origin server doesn’t have to work as hard as before. You can rely on CDN to uptake your traffic load. This will allow you to easily scale up your website and/or application.

Better Security & DDoS Protection

A CDN provides additional security. Since 60%+ of the traffic is being served through the CDN provider, CDNs will mitigate DDoS attacks for you on their edge servers.

Lower Costs

CDN in most cases reduces most of the website’s bandwidth consumption, which in return reduces the load/costs on the origin server.

What is Static Content?

Contents can be categorized into two while using CDN: Dynamic Content and Static Content.

Static content can be delivered to an end-user without having to be generated, modified, or processed. The server delivers the same file to each user, making static content one of the simplest and most efficient content types to be transmitted via a CDN.

What is Dynamic Content?

Dynamic content is the term used to describe site content that automatically adapts to various pre-defined conditions, such as particular user signals. The content featured on the website will adjust dynamically so that different users see different content. Dynamic web page: example of server-side scripting (PHP and MySQL).

Dynamic Content Acceleration: What is FEO (Front-end Optimization)?

The term “front end” relates to the interaction between your website and a user’s browser in the context of web services. Front end optimization (FEO), which is also known as content optimization, is the process of fine-tuning your website to make it more browser-friendly and load faster.

Broadly speaking, FEO focuses on reducing file sizes and minimizing the number of requests needed for a given page to load.

During the FEO process, web designers draw a distinction between the perceived and the actual page load time. Perceived load time is considered because of its impact on the overall user experience while the actual load time is often used as a performance benchmark metric.

How does using CDN affect SEO?

CDNs improve the speed and quality of content that is delivered to the clients. CDNs should be seen as a part of the solution for search ranking. Since CDNs will improve page speed, it will affect the ranking. It is good to know that CDN is not the only way to improve SEO yet it is still quite effective.

For instance, CDNs help to ensure each version of your website across several servers and locations are identical. CDNs use caching algorithms and canonical headers to help enhance the SEO of websites by combatting duplicate content creation issues.

It is obvious that web page load time impacts search rankings. CDNs play an important role in optimizing page speed and many people aren’t familiar with CDNs or the process in which they can improve page speed.

When it comes to SEO using a CDN will:

  • Improve the load time of your content

  • Reduce the open connections to your web server

  • Increase user experience and site performances

  • Lower image size sent to the user

  • Minimize traffic spikes at point of origin to save your website stability

  • Help scale in case of high traffic

Does CDN reduce DDOS attacks?

Many organizations mistakenly believe that Content Delivery Networks (CDN) provides a solution to stop DDOS attacks.

The fact is that a CDN merely addresses the symptoms of a DDOS attack. By absorbing these large volumes of data, a CDN actually let all the information into and through the network, also providing an “all are welcome” approach. In addition, most CDN based DDoS protection solutions only focus on absorbing HTTP/HTTPS DDOS attacks, ignoring all others such as NTP/DNS amplification attacks, which are very common.

CDNs offer two main forms of cloud-based DDOS solutions

  • Always-on solutions, which provide symmetric protection for regular operations,

  • On-demand solutions, which offer asymmetric protection for higher threat situations.

What is Anycast DNS?

Anycast is a networking technique where the same IP prefix is advertised from multiple locations. The network then decides where to route a user request, based on routing protocol expenses and possibly the ‘health’ of the advertising servers. There are several benefits of anycast.

  • In steady-state, users of an anycast service (DNS is an excellent example) will always connect to the ‘closest’ (from a routing protocol perspective) DNS server. This reduces latency, as well as providing a level of load-balancing (assuming that your consumers are evenly distributed around your network).

  • Another advantage is the ease of configuration management. Rather than having to configure different DNS servers depending on where a server/workstation is deployed (Asia, America, Europe), you have only one IP address that is configured in every location.

Packet latency is largely a function of geographic distance (It has other impacting factors too). With Anycast, we tell routers the same server is located at a bunch of different spots around the internet. Because internet routers are always optimizing routes they pick the one closest to the requester. Moving DNS servers closer, mitigates this geographic latency component. While lower latency is one of the most important benefits of Anycast DNS, we will also gain resilience at the same time.

Are CDNs valuable for video streaming?

A video CDN, video content distribution network, is a large geographically dispersed network of servers delivering live and on-demand, high-quality videos to web-connected devices. These specialized video streaming server networks accelerate delivery through caching, which stores content temporarily on multiple servers throughout the video CDN. When a viewer submits a request, the nearest content cashing server the user’s location delivers the video.

To keep up with increasing demand, network service providers realize the need to build their own content distribution networks supporting the VoD server (video-on-demand) and IPTV server (Internet Protocol Television) technology. Network service providers that deploy their own video CDN can benefit from:

  • Reducing traffic on the backbone network, which improves video content and web performance overall.

  • Creating and deploying value-added, targeted services to attract new customers and retain existing subscribers.

  • Content providers also benefit from a video CDN, as customer conversion rates increase and loyalty strengthens.

  • CDN video streaming can greatly accelerate the delivery of video media and make the environment more secure and reliable. CDNs provide a low latency viewing experience, which is the most important thing for user satisfaction.

When deciding what CDN to use, there are several factors that you consider:

  1. Geography – Are your viewers distributed all across the globe, or mainly concentrated to certain continents or countries like Asia, Europe, USA, China. The reason for pointing out is certain top tier CDNs have a low presence in Asia, especially China while some of the CDNs are generally built for specific areas. Many CDNs especially serve to the USA only.

  2. Scale – Are you watching live stream international sports events or Video on Demand services? Only a few CDNs in the world are currently efficient enough to cater to a huge scale worldwide specifically for live streaming.

  3. Pricing – Are you a startup that is more comfortable with pay-per-use pricing or are you able to commit considerable bandwidth beforehand. These are the questions you need to consider. Different CDNs cater to different business models.

Are CDNs effective for Mobile Users?

Based on the Cisco Annual Internet Report, Mobile connectivity is increasing dramatically every year. This makes it mandatory for mobile websites to be fast and responsive to user requests.

Several studies have reported that the visitors requesting content from their mobile devices can easily find a difference of at least 10% faster page upload on servers with a CDN in comparison to the response from sites without a CDN. Users on mobile devices expect performance to be at least similar if not better to what they get on their desktops. Mobile acceleration can also be improved by optimizing the locations of POPs. As a rule of thumb, serving contents from different locations closer to your end-user will help you improve your QoE and QoS.

What is Hybrid CDN?

Hybrid CDN is the solution for a medium-sized company. It basically means you are still using third-party CDN. But on the top of that content delivery, you are going to build your own platform, so you are boosting that third-party CDN. That is because commercial CDNs just simply provide a service for you and hundreds of other companies. So they can’t analyze performance for your personal use case If you want to make sure you are optimizing your content delivery you have to do yourself.

A Hybrid CDN mixes Private and Public CDNs to deliver live and Video-on-Demand content. It optimizes the cost, performance and resilience of your video service. Public CDN provides high availability. Private CDN provides cost-effective scalability.

What is Geoblocking?

Geoblocking is a measure used to limit end-users access to some of the contents based on their geographic location. The end user’s location is calculated using the geolocation technique. Then, the user’s IP address is checked against a blacklist or whitelist; the result of this check is used to determine whether the system will approve or deny access to the content, such as films, TV shows and sports events, primarily for copyright and licensing reasons. Other use cases for geoblocking are, such as blocking malicious traffic, enforcing price discrimination, location-aware authentication, fraud prevention or online gambling.

What is the difference between Push and Origin Pull method?

There are two methods for content distribution in CDN: Origin Pull and Origin Push. Based on how you would like to place your content on CDNs edge servers, you can choose one of them.

In the Origin Pull method, after deploying CDN on your origin server, the first request for the content will be retrieved from your origin server. Then it is cached and served to the requester. Next requests for the same content will be served directly from CDN’s Edge servers. In this method, you don’t need to transfer your content to CDN’s edge servers.

In the Origin Push method, you need to transfer your content to CDN. The transfer can be done using different methods such as FTP. Then CDN distributes these contents to edge servers.

What is difference in video performance between streaming and progressive download?

When you store your video files on a conventional Web server and the files are downloaded through HTTP, then we are talking about “Progressive Download”. Progressive (HTTP) download is the most common method for transferring files over the Internet: when you visit a Web site, all of its elements, text and images, are transferred in this way.

Contrary to Progressive Download, Streaming is accomplished through specialized Media Servers which are optimized for transferring digital video/audio. The transference is managed by messages that are sent/received between the WebTV (Video Player) and the Media Server.

Who needs CDN?

CDNs are ultimately responsible for the performance and user experience of any online service that depends on fast, low latency delivery of files, images, scripts and other contents.

They are fundamental to online broadcasters and other Over-The-Top (OTT) service providers, who either build their own private network for content delivery or partner with a CDN service provider. CDNs provide a revenue stream for companies with distributed network infrastructure, such as ISPs, who can monetize that infrastructure by using it to take CDN services to market and use CDNs to control traffic flow across that infrastructure, to reduce costs.