Error 521: Web server is down
Cloudflare could not connect to your origin
Seen in Cloudflare
The origin refused Cloudflare's connection.
Common causes
- The web server is stopped.
- The origin firewall blocks Cloudflare's IP ranges.
- The origin listens on a different port than Cloudflare uses.
How to fix it
- Start the web server and check it listens on 80/443.
- Allow Cloudflare's published IP ranges.
- Match the origin port to the SSL mode.
Got a different message? Paste it into the error explainer.
Related errors
- Error 522: Connection timed out · Cloudflare timed out connecting to your origin
- 504 ERROR The request could not be satisfied · CloudFront timed out waiting for the origin
- 502 Bad Gateway · The proxy got a bad response from the server behind it
- 503 Service Unavailable · The server is temporarily unable to handle requests
- 504 Gateway Timeout · The server behind the proxy took too long
- Error 520: Web server is returning an unknown error · Cloudflare got an empty or invalid response
- Error 525: SSL handshake failed · Cloudflare could not complete TLS with your origin
- Error 526: Invalid SSL certificate · Cloudflare doesn't trust your origin's certificate
- 429 Too Many Requests · You've hit a rate limit
- 400 Bad Request · The server could not understand the request
- 401 Unauthorized · The request needs valid credentials
- 403 Forbidden · The server refuses to allow this request