---
title: CDN-Loop
summary: null
url: https://www.fastly.com/documentation/reference/http/http-headers/CDN-Loop
---

The `CDN-Loop` header is appended by Fastly (and other CDN providers) when a request transits the network. It is similar to the `Fastly-FF` header, in that it can be used to detect infinite loops in edge logic.

Unlike `Fastly-FF`, the `CDN-Loop` header is recognized and modified by other cloud platform providers.

## Examples

If a user visits a domain that resolves to Fastly, and we forward that request to your origin server, the request will have an added `CDN-Loop` header with up to four "Fastly" tokens listed depending on whether your service is configured to use [Clustering](https://www.fastly.com/documentation/guides/vcl/clustering/) and [Shielding](https://www.fastly.com/documentation/guides/concepts/shielding/):

```
CDN-Loop: Fastly, Fastly
```

In this example, a user has visited a domain that resolves to `OtherProvider`, and that provider has forwarded the request to Fastly:

```
CDN-Loop: OtherProvider, Fastly
```