Getting 521 error

Hi iam having so many issues after using Cloudflare first i was facing error 520 then 1016 then now 521
What it is this what is the use of Cloudflare than its happens automatically gets solved and again it shows the same error 521 till now what to do Cloudflare please help me.

Common causes

The two most common causes leading to Error 521 are:

The web server is offline

The origin web server process (e.g., Apache or Nginx) might not be running or has crashed. In that case:

  • Ensure your web server is running normally.
  • Review the server’s error logs to see what is causing the error.

If you’re unable to perform these tasks, contact your host provider.

Cloudflare requests are blocked

The origin web server or hosting provider’s network might be blocking Cloudflare’s requests.

As a reverse proxy, Cloudflare connects to your server from a Cloudflare IP and all subsequent traffic comes exclusively from a smaller set of Cloudflare IPs. As a result, certain server-side security solutions might mistake the increase in legitimate connections from this smaller set of IPs as an attack. This results in some Cloudflare IPs being blocked or rate-limited.

To resolve this issue, whitelist all Cloudflare IP ranges in your server’s firewall or any other security software at the origin. See the list of Cloudflare IP ranges.

If you’re unable to whitelist Cloudflare IPs, contact your host provider.


In short, you are using some sort of security solution (i.e. IDS/IPS) which is triggered by CF servers and block them occasionally.

Whitelist Clouldflare IPs in your security solution. If you need to be completely hidden to the outside world, here is a good solution based on port knocking.


A 520 means your web server isn’t responding to Cloudflare. You would have to check your server logs to see why.

Cache duration in Cloudflare depends on how often your content changes.

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