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5xx · Server Error

521 Web Server Is Down

A Cloudflare error meaning the origin server refused the connection.

What it means

HTTP 521 is a non-standard Cloudflare status returned when Cloudflare cannot establish a connection to the origin server because the origin actively refused it. The edge is healthy; the server behind it is down or is rejecting connections from Cloudflare.

When it happens

It happens when the origin web server has crashed or been stopped, when its firewall or security rules block Cloudflare's IP ranges, or when the service is not listening on the expected port.

How to fix it

  • Confirm the origin web server is running and listening on the correct port.
  • Whitelist Cloudflare's IP ranges in the origin firewall and any security software.
  • Restart the web server if it has crashed.
  • Check that the DNS record points to the correct origin IP address.

SEO impact

Damaging if sustained. Crawlers see a server error and cannot index the page. A down origin behind Cloudflare needs fixing quickly to avoid crawl-rate and ranking loss.

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Related codes

500 Internal Server Error

A generic error meaning the server encountered an unexpected condition.

501 Not Implemented

The server does not support the functionality required to fulfil the request.

502 Bad Gateway

A server acting as a gateway received an invalid response from the upstream server.

503 Service Unavailable

The server is temporarily unable to handle the request, often due to overload or maintenance.

504 Gateway Timeout

A gateway server did not receive a timely response from the upstream server.

505 HTTP Version Not Supported

The server does not support the HTTP protocol version used in the request.

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