i added ip4 of cloudfare into iptables but still when i go to my website using https i get Error 521 : Web server is down. Please help its urgent

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Hello there,

Error 521 occurs when the origin web server refuses connections from Cloudflare. Security solutions at your origin may block legitimate connections from certain Cloudflare IP addresses.

You can also make sure that port 443 is open with this command:

  • iptables -A INPUT -p tcp -m tcp --dport 443 -j ACCEPT

Also, you can check our tutorial for whitelisting IPs with iptables:



by Mitchell Anicas
Iptables is a software firewall for Linux distributions. This cheat sheet-style guide provides a quick reference to iptables commands that will create firewall rules that are useful in common, everyday scenarios. This includes iptables examples of allowing and blocking various services by port, network interface, and source IP address.