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CDN Support Overview

Updated on Nov 3, 2026

Telerik UI for ASP.NET AJAX can load the control scripts and skins from a Content Delivery Network (CDN) instead of serving them from the application. The CDN support 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 scripts and skins 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 has a number of advantages:

Reduced latency – requests will be automatically redirected to the nearest server
Better use of caching – each resource only needs to be downloaded once
Reduced hosting load – the resources are delivered by the CDN instead of your web server

Note that the RadScriptManager does NOT combine the web resources needed for the Telerik controls in a single request when the CDN is enabled.

Caching is what a CDN is all about. Say you have a number of applications that all utilize RadGrid. A customer will load the RadGrid scripts just once and then use the cached version until they clear the browser cache. Proxies will also aggressively cache these resources.

When NOT to use CDN?

Intranet scenarios often do not benefit from external CDNs, as internal networks can provide lower latency and do not depend on external connectivity.
When you are using an internal build (not an official one).

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 (or Auto and EnableCdn is true on the RadScriptManager) and you have not changed BaseUrl and BaseSecureUrl, or they still point to one of the discontinued Telerik hosts listed above, the scripts are served from the Telerik.Web.UI assembly, exactly as if TelerikCdn was Disabled. 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 scripts, and Content Security Policy (CSP) rules.
If you do not need a CDN, set TelerikCdn to Disabled (or remove the setting) to serve the resources 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 resources are served from the assembly otherwise. Since the Telerik CDN is discontinued, EnableCdn="true" alone (without custom BaseUrl and BaseSecureUrl) loads only the Microsoft AJAX scripts from the Microsoft CDN, while the Telerik scripts are served from the assembly. To load the Telerik scripts from a CDN, set TelerikCdn to Enabled and specify your own base URLs.

The Telerik script CDN settings take effect only through the RadScriptManager. The standard asp:ScriptManager does not apply these settings, so EnableCdn="true" on it loads only the Microsoft AJAX scripts from the Microsoft CDN, while the Telerik scripts are served from the assembly through the standard ScriptResource.axd handler. The CDN delivery of the skins is configured independently through the RadStyleSheetManager.

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 resources from a CDN, always specify your own base URLs as described in the Custom CDN Provider article.

The RadStyleSheetManager has the same configuration for enabling the CDN and for convenience, the examples below show enabling the CDN for the styles along with the scripts. In the examples, my.favorite.cdn stands for your own CDN host, which hosts the resources as described in the Custom CDN Provider article.

CDN support will be enabled ONLY for:

Official Major Releases

Official Service Packs

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 RadScriptManager and RadStyleSheetManager:

ASPNET

<telerik:RadScriptManager 
	ID="RadScriptManager1"    
	runat="server"    
	CdnSettings-TelerikCdn="Enabled"
	CdnSettings-BaseUrl="http://my.favorite.cdn"
	CdnSettings-BaseSecureUrl="https://my.favorite.cdn">
</telerik:RadScriptManager>

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

Another way to set these properties is to use the composite property of RadScriptManager and RadStyleSheetManager:

ASPNET

<telerik:RadScriptManager 
	ID="RadScriptManager1" 
	runat="server">
	<CdnSettings TelerikCdn="Enabled" BaseUrl="http://my.favorite.cdn" BaseSecureUrl="https://my.favorite.cdn" />
</telerik:RadScriptManager>

<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 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.StyleSheetManager.* keys enable the CDN support for the CSS and image files for the skins. The scripts and the skins 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 (<CdnSettings TelerikCdn="Enabled" BaseUrl="..." BaseSecureUrl="..." />), the RadScriptManager and RadStyleSheetManager render 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.

The rendered URLs have the {BaseUrl}/ajax/{version}/... or {BaseUrl}/ajaxz/{version}/... format, where {version} is the short version of the Telerik.Web.UI assembly (for example, 2025.2.609). Make sure the folder structure on your CDN matches it.

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.

More Optimizations

To further optimize the load of the scripts you can download the Microsoft ASP.NET AJAX scripts from the Microsoft CDN by setting EnableCdn="true":

ASPNET

<telerik:RadScriptManager 
	runat="server" 
	ID="RadScriptManager1" 
	EnableCdn="true"> 
	<CdnSettings TelerikCdn="Enabled" BaseUrl="http://my.favorite.cdn" BaseSecureUrl="https://my.favorite.cdn" />
</telerik:RadScriptManager>
<telerik:RadStyleSheetManager 
	runat="server" 
	ID="RadStyleSheetManager1">    
	<CdnSettings TelerikCdn="Enabled" BaseUrl="http://my.favorite.cdn" BaseSecureUrl="https://my.favorite.cdn" />
</telerik:RadStyleSheetManager>

Both MS AJAX scripts and Telerik resources will be served from the respective CDNs.

Additional Resources

Configure Local CDN