3. The CDN-Cache-Control Targeted Field

The CDN-Cache-Control response header field is a targeted field (Section 2) that allows origin servers to control the behavior of CDN caches interposed between them and clients separately from other caches that might handle the response.

It applies to caches that are part of a distributed network that operate on behalf of an origin server (commonly called a CDN).

CDN caches that use CDN-Cache-Control will typically forward this header so that downstream CDN caches can use it as well. However, they MAY remove it when this is undesirable (for example, when configured to do so because it is known not to be used downstream).

3.1. Examples

For example, the following header fields would instruct a CDN cache (i.e., a cache with a target list of [CDN-Cache-Control]) to consider the response fresh for 600 seconds, other shared caches to consider the response fresh for 120 seconds, and any remaining caches to consider the response fresh for 60 seconds:

Cache-Control: max-age=60, s-maxage=120
CDN-Cache-Control: max-age=600

These header fields would instruct a CDN cache to consider the response fresh for 600 seconds, while all other caches would be prevented from storing it:

CDN-Cache-Control: max-age=600
Cache-Control: no-store

Because CDN-Cache-Control is not present, this header field would prevent all caches from storing the response:

Cache-Control: no-store

Whereas these would prevent all caches except for CDN caches from storing the response:

Cache-Control: no-store
CDN-Cache-Control: none

(Note that 'none' is not a registered cache directive; it is here to avoid sending a header field with an empty value, which would be ignored.)