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CDN Support Overview

Updated on Nov 3, 2026

Telerik UI for ASP.NET AJAX can load the control skins (CSS and images) from a Content Delivery Network (CDN) instead of serving them from the application. This feature has been available since Q3 2009 SP1 and is included in all supported versions.

The Telerik-hosted CDN is discontinued. Starting with the November 11, 2026 release, new versions of the Telerik UI for ASP.NET AJAX skins and scripts are no longer published to the Telerik CDN (the Amazon CloudFront and telerikstatic.com hosts). The files of the versions that are already published remain accessible, but no new releases, service packs, or bug fixes will be added to them. To use a CDN with newer versions, host the resources yourself or use a CDN provider of your choice. For more information, see the Telerik CDN Is Discontinued section below and the Custom CDN Provider article.

Using a Content Delivery Network offers several benefits:

Reduced latency - requests are routed to the nearest CDN edge location
Improved caching - resources are downloaded once and reused across sites and sessions
Reduced hosting load - CDN delivery reduces bandwidth and hosting costs on your server

Caching is a key advantage. For example, if multiple applications use RadGrid, a user downloads the RadGrid CSS and images once, then continues using the cached resources until the browser cache is cleared. Network proxies may also cache these files aggressively.

When NOT to use CDN

CDN usage may not be ideal in cases such as:

Intranet environments - internal networks are often faster than external CDNs and may block external resource requests
Offline or restricted networks - CDN requires internet access
Internal or development builds - CDN is available only for official release versions

Telerik CDN Is Discontinued

Starting with the November 11, 2026 release, the Telerik CDN no longer receives new versions of the Telerik UI for ASP.NET AJAX resources. This affects the following hosts that were used by the built-in CDN support:

https://d2i2wahzwrm1n5.cloudfront.net - scripts
https://d35islomi5rx1v.cloudfront.net - skins (CSS and images)
http(s)://aspnet-scripts.telerikstatic.com - scripts
http(s)://aspnet-skins.telerikstatic.com - skins (CSS and images)

The files of the versions that were published before the discontinuation remain accessible, so applications that use older versions continue to work.

What happens when you upgrade

When you upgrade to a version that no longer has resources on the Telerik CDN, the following behavior applies:

If TelerikCdn is Enabled and you have not changed BaseUrl and BaseSecureUrl, or they still point to one of the discontinued Telerik hosts listed above, the skins are served from the embedded resources of the assemblies, exactly as if TelerikCdn was Disabled. The Default skin is located in Telerik.Web.UI.dll, while the other built-in skins are located in Telerik.Web.UI.Skins.dll, so the version-matched Skins assembly must be deployed with the application (see Skins Location). With these assemblies available, you do not need to change your code or web.config to keep the application working, but the resources are no longer delivered by a CDN.
If BaseUrl and BaseSecureUrl point to your own host or CDN provider, they continue to work as before. See the Custom CDN Provider article.
Because the resources are served from the assembly in the first scenario, the combined request (CombinedResource) is not applied either, as it requires a working CDN.

If you want to keep the benefits of a CDN with the new releases, follow the steps in the Custom CDN Provider article to host the resources on your own server or on a commercial CDN provider, such as Cloudflare, Amazon CloudFront, or Azure Front Door. The CDN resource package is available for download in your Telerik account.

The Telerik UI for ASP.NET AJAX resources are not published as an npm package and are not available through public CDNs such as jsDelivr or unpkg.

Recommended actions

Remove any hard-coded references to the discontinued Telerik CDN hosts from your pages, master pages, custom stylesheets, and Content Security Policy (CSP) rules.
If you do not need a CDN, set TelerikCdn to Disabled (or remove the setting) to serve the skins from the assembly.
If you need a CDN, configure a custom CDN provider.

How to enable the CDN support

By default, TelerikCdn is set to Auto. In this mode, the Telerik CDN is used only when EnableCdn is set to true on the RadScriptManager, and the skins are served from the assembly otherwise. Since the Telerik CDN is discontinued, EnableCdn="true" alone (without custom BaseUrl and BaseSecureUrl) does not load the skins from a CDN. To load the skins from a CDN, set TelerikCdn to Enabled and specify your own base URLs.

The skins are loaded from a CDN only when a RadStyleSheetManager is added to the page. Without it, the skins are served from the assembly through the standard ASP.NET WebResource.axd handler, even if the RadScriptManager uses a CDN.

Since the Telerik CDN is discontinued for new releases, enabling TelerikCdn without a custom BaseUrl and BaseSecureUrl results in serving the resources from the assembly. To load the skins from a CDN, always specify your own base URLs as described in the Custom CDN Provider article.

Host the Telerik UI for ASP.NET AJAX resources for your version on your own server or CDN provider, as described in the Custom CDN Provider article.
Set the CdnSettings-TelerikCdn, CdnSettings-BaseUrl and CdnSettings-BaseSecureUrl properties of the RadStyleSheetManager (my.favorite.cdn stands for your own CDN host):

ASPNET

<telerik:RadStyleSheetManager 
    ID="RadStyleSheetManager1" 
    runat="server" 
    CdnSettings-TelerikCdn="Enabled"
    CdnSettings-BaseUrl="http://my.favorite.cdn"
    CdnSettings-BaseSecureUrl="https://my.favorite.cdn" />

Another way to set these properties is to use the composite <CdnSettings> property of RadStyleSheetManager:

ASPNET

<telerik:RadStyleSheetManager 
    ID="RadStyleSheetManager1" 
    runat="server">
    <CdnSettings TelerikCdn="Enabled" BaseUrl="http://my.favorite.cdn" BaseSecureUrl="https://my.favorite.cdn" />
</telerik:RadStyleSheetManager>

Moreover, you can enable the CDN support globally by adding the following keys in the <appSettings> section of your web.config file:

XML

<appSettings>   
    <add key="Telerik.ScriptManager.TelerikCdn" value="Enabled" />   
    <add key="Telerik.ScriptManager.TelerikCdn.BaseUrl" value="http://my.favorite.cdn" />   
    <add key="Telerik.ScriptManager.TelerikCdn.BaseSecureUrl" value="https://my.favorite.cdn" />   
    <add key="Telerik.StyleSheetManager.TelerikCdn" value="Enabled" />
    <add key="Telerik.StyleSheetManager.TelerikCdn.BaseUrl" value="http://my.favorite.cdn" />
    <add key="Telerik.StyleSheetManager.TelerikCdn.BaseSecureUrl" value="https://my.favorite.cdn" />
</appSettings>

Note, that the Telerik.ScriptManager.* keys enable the CDN support for the JavaScript files. The skins and the scripts are served from separate base URLs, so you can host them on different origins.

How are my users affected?

When the CDN support is enabled with a custom BaseUrl and BaseSecureUrl, the RadStyleSheetManager renders CDN URLs that match the page protocol: BaseUrl is used for HTTP requests and BaseSecureUrl for HTTPS requests. The framework renders the URLs based on the page request scheme, and modern browsers may upgrade requests to HTTPS (HSTS, corporate policies, etc.), so it is recommended that your CDN supports HTTPS.

Note: If your environment uses firewalls, proxies, or strict corporate security policies, ensure that your CDN domain is allowed. Otherwise, disable CDN support to serve resources locally.