> ## Documentation Index
> Fetch the complete documentation index at: https://gcore-doc-1894.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# CDN 4xx response troubleshooting

A 4xx response can come from the CDN or origin when a request is invalid, access is denied, or the requested content does not exist.

## Status-specific causes

The response code helps identify which request or access setting to check.

* `400 Bad Request`: Verify the request syntax and the Host header expected by the origin.
* `401 Unauthorized` and `403 Forbidden`: Check authentication credentials, CDN access policies, secure tokens, and origin access control lists (ACLs).
* `404 Not Found`: Verify that the requested path is correct and that the content exists on the origin.
* `405 Method Not Allowed`: Verify that the CDN resource and origin support the request method.

## Origin content availability

Request the affected content directly from the origin and confirm an HTTP `200` response:

```bash theme={null}
curl -sS -D - -o /dev/null https://origin.example.com/path/to/content
```

When the origin uses name-based virtual hosting, send its expected Host header:

```bash theme={null}
curl -sS -D - -o /dev/null http://192.0.2.10/path/to/content \
  -H "Host: origin.example.com"
```

For HTTPS, use `--resolve` to connect to the origin IP while preserving the hostname for the Host header and TLS:

```bash theme={null}
curl -sS -D - -o /dev/null \
  --resolve origin.example.com:443:192.0.2.10 \
  https://origin.example.com/path/to/content
```

If the origin uses an IP allowlist or a DDoS Protection service, allowlist CDN edge IPs. Retrieve the current public IP list:

```bash theme={null}
curl -i -X GET https://api.gcore.com/cdn/public-ip-list
```

The public IP list changes over time, so keep the allowlist updated with a recurring script. The [Origin ACL](/cdn/getting-started/configure-an-origin/add-cdn-servers-to-the-origin-acl-whitelist) guide covers allowlisting CDN edges. Origin access control can also use [request headers](/cdn/cdn-resource-options/http-headers/specify-http-headers-that-cdn-adds-to-requests-to-the-origin) that the CDN adds when pulling content.

## CDN resource settings

Check the resource status and origin request settings before retesting the affected URL.

* Confirm that the CDN resource is active. After creating a new resource, wait until the configuration is applied on CDN edges — usually about 15 minutes.
* Select an **Origin pull protocol** so the origin can respond to requests from CDN edges. The [Origin pull](/cdn/cdn-resource-options/general/specify-an-origin-and-the-origin-pull-protocol) option controls which scheme the CDN uses when requesting content from the origin.
* Enable **Change Host header** and set a value that matches the origin or the host configured on the origin. The [Host header](/cdn/cdn-resource-options/http-headers/configure-and-check-the-host-header) option controls which virtual host the origin uses.

After changing **Origin pull protocol** or **Change Host header**, click **Save changes** before retesting the request.

## 4xx response tracking and logs

The **Response codes** report tracks 4xx responses for CDN resources.

<Steps>
  <Step title="Open CDN">
    In the [Gcore Customer Portal](https://portal.gcore.com), select **CDN**.
  </Step>

  <Step title="Open CDN statistics">
    Navigate to **Reports** → **Statistics**.
  </Step>

  <Step title="View response codes">
    Select **Response codes**.
  </Step>
</Steps>

The [Log viewer](/cdn/logs/log-viewer-view-and-download-cdn-resource-logs) shows recent request details. For long-term log export, [Logs uploader](/cdn/logs/logs-uploader) is a paid option that must be enabled by support. To activate it, contact the account manager or [Gcore Support](mailto:support@gcore.com).

If you need to open a support ticket for a specific failed request, include the `traceparent` header from the CDN response if possible — it uniquely identifies the request and allows Gcore Support to locate it in Gcore systems. See [Traceparent header for troubleshooting](/cdn/troubleshooting/traceparent-header-for-troubleshooting).