Getting 521 error even port is open for 443

Website is showing 521 error eventhough the port is opened for 443. the website is running behind IIS windows

Hello rohit.singh

The 521 error suggests that Cloudflare is unable to establish an SSL/TLS handshake with your origin server. To fix this:

  1. Verify that the port 443 is really open using a tool like
  2. Confirm that your server is running with a valid certificate. You can do this by running the server IP address through an SSL Checker like
  3. Ensure your firewall is not blocking Cloudflare’s requests. You may need to allowlist Cloudflare’s IP ranges.
  4. Check if your server is properly configured for HTTPS request. In your case, since you’re using IIS windows, confirm that the HTTPS binding is correctly configured.

If all these are in order and you’re still facing the issue, it would be best to get in touch with your hosting provider for further investigation.


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