521 Web Server Is Down
The origin server refused the connection from Cloudflare.
What to do
The origin refused Cloudflare's connection. Check the web server is running, and that a firewall is not blocking Cloudflare's IP addresses.
- Class
- 5xx Server Error. The server failed to fulfill a request that looked valid.
- Registered
- No. Cloudflare sends it, and it is not in the IANA registry, so other servers may mean something else by it.
- References
- Cloudflare
Every 5xx code
- 500 Internal Server Error
- 501 Not Implemented
- 502 Bad Gateway
- 503 Service Unavailable
- 504 Gateway Timeout
- 505 HTTP Version Not Supported
- 506 Variant Also Negotiates
- 507 Insufficient Storage
- 508 Loop Detected
- 510 Not Extended
- 511 Network Authentication Required
- 520 Web Server Returns an Unknown Error
- 521 Web Server Is Down
- 522 Connection Timed Out
- 523 Origin Is Unreachable
- 524 A Timeout Occurred
- 525 SSL Handshake Failed
- 526 Invalid SSL Certificate
- 530 (No name)
- 561 Unauthorized