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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.

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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.

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Origin content availability

Request the affected content directly from the origin and confirm an HTTP 200 response:
When the origin uses name-based virtual hosting, send its expected Host header:
For HTTPS, use --resolve to connect to the origin IP while preserving the hostname for the Host header and TLS:
If the origin uses an IP allowlist or a DDoS Protection service, allowlist CDN edge IPs. Retrieve the current public IP list:
The public IP list changes over time, so keep the allowlist updated with a recurring script. The Origin ACL guide covers allowlisting CDN edges. Origin access control can also use request headers that the CDN adds when pulling content.

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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 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 option controls which virtual host the origin uses.
After changing Origin pull protocol or Change Host header, click Save changes before retesting the request.

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4xx response tracking and logs

The Response codes report tracks 4xx responses for CDN resources.
1

Open CDN

In the Gcore Customer Portal, select CDN.
2

Open CDN statistics

Navigate to Reports → Statistics.
3

View response codes

Select Response codes.
The Log viewer shows recent request details. For long-term log export, Logs uploader is a paid option that must be enabled by support. To activate it, contact the account manager or Gcore Support. 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.