Troubleshooting error code : 521

Answer these questions to help the Community help you get started.

What is the domain name?

  • Response : [Cannot attach links]

Have you searched for an answer?

  • Response : Yes

Please share your search results url:
[Cannot attach links]

When you tested your domain using the [Cloudflare Diagnostic Center], what were the results?

  • Question : Are the Cloudflare nameservers configured correctly in the site?
    Answer : Looking Good!

  • Question : Does the site have valid DNSSEC records?
    Answer : Error Found

  • Question : Check DS record configuration?
    Answer : Error Found

  • Question : Is there an A or AAAA DNS record to make connecting to ‘[Cannot attach links]’ possible?
    Answer : Looking Good!

  • Question : Check if connecting to ‘[Cannot attach links]’ works
    Answer : Error Found
    Reason : No, Cloudflare DNS could not connect to ‘[Cannot attach links]’

  • Question : Does the domain have an MX record?
    Answer : Looking Good!

  • Question : Does the request result in a redirect loop?
    Answer : Looking Good!

  • Question : Does the site respond with a succesful HTTPS status?
    Answer : Error Found
    Reason : fail - No, your request failed with a response status of 400 or above.

  • Question : Does the website redirect unencrypted traffic from HTTP to HTTPS?
    Answer : Looking Good!

  • Question : How well does the website support encryption via an SSL/TLS certificate?
    Answer : Looking Good!

  • Question : Does the website mix encrypted and non-encrypted content?
    Answer : Error Found
    Reason : response_non_200 – The site’s web server responded with a status code that isn’t 200 (OK).

  • Question : How fast is the page response time?
    Answer : Looking Good!


Describe the issue you are having:

I have a webserver, which is an IP address, which was setup to Cloudflare using this configuration ;, and for some reason the WebServer (Contabo VPS) is not connecting, or responding to Cloudflare,
[Cannot attach links]

What error message or number are you receiving?
Web server is down [Error code 521]

What steps have you taken to resolve the issue?

  1. Firewall Configuration [Disabled]
  2. None, [Out of ideas]

Was the site working with SSL prior to adding it to Cloudflare?

  • No, since the webpage did not contain any content, before

What are the steps to reproduce the error:

  1. Navigate to website, [Cannot attach links]
  2. Complete the captcha
  3. Wait, for redirect, and the error screen is presented,

Have you tried from another browser and/or incognito mode?

  • Yes

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