Error code
Cloudflare 521
CLOUDFLARE521
Network Error Code· An error code from a CDN, proxy, or network edge service such as Cloudflare.
What it means
The origin web server refused the connection from Cloudflare.
How to fix it
- not listening on port 80 or 443.
Not affiliated with Cloudflare. Answer summarized from the manufacturer's manual linked above; consult that source for the authoritative procedure.
More Cloudflare codes
- 1000Cloudflare's DNS resolution points to a prohibited or loopback IP address
- 1001DNS resolution failed for the requested hostname
- 1003Direct access to Cloudflare's IP address without a valid Host header is not permitted
- 1006The visitor's IP address has been banned by the site owner using a Cloudflare firewall rule
- 1007The visitor's IP address has been banned by the site owner using a Cloudflare firewall rule
- 1008The visitor's IP address has been banned by the site owner using a Cloudflare firewall rule
- 1009Access is denied because the visitor's country is blocked by a Cloudflare country-based firewall rule
- 1010Cloudflare detected that the browser's user-agent or request pattern matches a known malicious signature and blocked access
- 1012The website is unavailable in your region due to a Cloudflare access restriction or legal requirement
- 1014A CNAME record in one Cloudflare account points to a domain in a different Cloudflare account
- 1015The visitor is being rate limited by a Cloudflare Rate Limiting rule configured by the site owner
- 1016Cloudflare could not resolve the origin DNS hostname configured in the site's DNS settings