Error 521 occurs when Cloudflare is unable to connect to your server. This error occurs because of server downtime or the server not responding to Cloudflare’s requests. However, you can fix this error with simple steps like:  

  • Verifying SSL/TLS settings 
  • Making sure DNS settings are correctly configured 
  • Checking server logs for errors  
  • Ensuring your server is responsive  
  • Making sure your server’s firewall is not blocking Cloudflare’s IP address  

In this article, we will discuss how to fix the Cloudflare 521 error in detail. But before that, let us understand what error 521 is in detail. 

What is Error 521? 

When someone tries to visit a website that uses Cloudflare’s Content Delivery Network (CDN), here is what happens: 

  1. The web browser first connects to Cloudflare. 
  2. Then, Cloudflare reaches out to the website’s original server to load the content. 

Error 521 happens when Cloudflare cannot connect to the website’s original server. However, that is not the only reason for error 521. Let us look at other reasons for this error.

What Causes Error 521?  

  1. Web server is offline: The original server might be down, or there could be an issue with server software like Apache or Nginx.  
  2. Cloudflare IPs are blocked or blacklisted: Since all traffic comes through Cloudflare’s IPs, the server’s security settings might block these IPs if it detects too many requests.  
  3. Misconfigured origin server: The original server needs to be set up correctly to work with Cloudflare. If not, it can cause this error.  
  4. Apache modules blocking requests: Security modules designed to prevent attacks may unintentionally block Cloudflare’s requests if not configured properly. 

How to Fix Error 521  

Here are six ways to fix this error:  

  • Check if the Web Server is working  

Typically, Cloudflare error 521 occurs when your website’s server goes offline, is under maintenance, or is facing downtime. If you know how to use Terminal, run the “PING” command (Linux), or Traceroute (Windows) to check your server’s status. Meanwhile, if you cannot access your server, contact BigRock’s customer support team for help.

  • Test Your Server’s Connection  

Sometimes, firewalls or security settings on your server might block Cloudflare’s IP addresses. Re-configuring the security settings can help fix the Cloudflare 521 error. You can do that by:  

  1. Safelist Cloudflare IPs: Adding Cloudflare’s IPs into a safelist ensures that your server does not block Cloudflare from accessing your website. Here are three ways you can do it:  
  2. Add Cloudflare’s IP addresses to your server’s .htaccess file. The code will look like this: allow from    
  3. You can go to your hosting provider’s control panel, in this case, BigRock’s cPanel and navigate to the “Advanced” option. You will see the “IP manager” option; click on it and add the IPs there.  
  4. Disable Security Modules on Apache Servers. Turn off modules like “mod_antiloris” and “mod_reqtimeout”, which block IPs that make too many requests.

  • Check Your Encryption Settings 

Cloudflare uses encryption to connect to your web server, and incorrect settings can cause error 521. Here is how to fix error 521:  

  • Go to the Cloudflare dashboard and click “SSL/TLS” settings  
  • Choose the correct encryption mode:  
  1.  -Flexible: Use if your site does not have an SSL certificate. 
  2.  -Full: Use if your site has an SSL certificate.   
  3.  -Strict: Use for advanced SSL configurations (requires extra steps).  
  • If you are unsure, turn on the “SSL/TLS Recommender” for Cloudflare to suggest the best settings.

  • Check for Website Issues  

Sometimes, issues with your website can lead to the Cloudflare 521 error. That is when you must disable Cloudflare and check if the error disappears temporarily. It may take a few hours to reflect fully. However, purge the Cloudflare cache from the dashboard if you want to speed up the process.

  • Clear Your Server Cache  

Clearing your server’s cache helps ensure that Cloudflare requests fresh resources, making it easier for the server to handle them. Log into your website’s backend and clear the server cache to do this. If you are unsure how to do this, contact your hosting provider for assistance. Once the cache is cleared, refresh your website and see if the error 521 message is gone. If it disappears, then clearing the cache resolves the issue!

  • Upgrade Your Hosting Plan 

If your website is experiencing high traffic, upgrading your hosting plan could be the ideal solution. Switching to a dedicated server or cloud server ensures that your website gets sufficient resources to handle the traffic efficiently. These hosting options provide better performance, scalability, and reliability compared to shared hosting.

Resolving Other Cloudflare Errors

You may encounter other Cloudflare errors, like “Error 520” or “Error 522.” Here is how to handle them:

  • Error 520: Web Server Returning an Unknown Error   

This happens when the original web server crashes or sends an unexpected response. You can:  

  1. Check if the server is running smoothly 
  2. Review the response headers for a clue 
  3. Temporarily disable the `.htaccess` file to identify potential misconfigurations.
  • Error 522: Connection Timed Out 

This error is usually caused by server overload, too many requests overwhelming the server, or firewall restrictions. Here is how to fix Error 522:   

  • Ensure your server is not overloaded.  
  • Safelist Cloudflare IPs in your server’s firewall settings.  
  • Enable KeepAlive messages to maintain persistent connections.  
  • Review your Cloudflare DNS settings to ensure everything is configured correctly. 

If these issues continue, contact your hosting provider or Cloudflare support for further assistance. 

Summing Up  

You now know what causes the “Error 521: Web server is down” message and how to troubleshoot and resolve it. By following the steps outlined in this guide, you can fix the issue and take steps to prevent it from recurring in the future.

Remember that error 521 is just one of many error messages that can occur on websites using Cloudflare’s CDN. Regular maintenance, proper server configuration, and monitoring can minimize such issues and ensure your site runs smoothly without your web hosting provider’s intervention.  

If you have any questions, refer to our FAQs for more clarity!  

Frequently Asked Questions (FAQs)  

  • How can I avoid getting “Error 521“? 

You can avoid the 521 error by ensuring that your original server is always running and operational. Additionally, review your server’s firewall and security settings to ensure Cloudflare IPs are not being blocked.  

  • How can I clear my Cloudflare cache? 

You need to log into your Cloudflare account to clear the entire cache. Click on “Purge Everything,” then confirm by clicking on “Purge Everything” again. The process typically takes up to 30 seconds. To remove specific items from the cache, use the “Custom Purge” option.  

  • Is “Error 521” a frequent issue for Cloudflare users? 

No, this error is rare for Cloudflare users. It usually signals a problem with the original server rather than Cloudflare itself.  

  • Do I need server access to resolve “Error 521“? 

Yes, resolving this error requires troubleshooting your origin server. If you are unable to fix it yourself, reach out to your hosting provider for assistance. BigRock users can contact their customer support team for help any time of the day.  

We’d love to hear from you! Share your thoughts or questions in the comments below!