Cloudflare IIS Proxy Error


I’m hosting a webserver on an IIS server pointing a record to my IP address from Cloudflare.

When unproxied (grey cloud) I’m able to reach the site.
When I proxy Cloudflare (orange cloud) I’m unable to reach the site.

I have disabled Windows Firewall to no avail. No other security software’s are running.

Does IIS have some sort of special option to enforce original IP address? or what is the issue here, help would be appreciated.

Again, site works when unproxied using the domain, when proxied the site refuses to work error 521.

Check the logs on your server to see what happens when you try to connect to it while the DNS record is proxied. What’s your SSL Mode set to in the Cloudflare dashboard? Assuming you have a valid SSL certificate on your server (which you hopefully do) make sure you’re set to Full(Strict), as Flexible can cause a redirect loop, easily visible in the server logs.

Do you mean so that the server sees the actual visitor IPs instead of Cloudflare IPs? I don’t use IIS but there is a section at

1 Like

Thanks for your comment, There are no logs Cloudflare just does not like port 443. If I use port 8443 everything works without issues, change back to port 443 and boom error 521, it does not even attempt to connect to my web server just gives the error straight away.

This topic was automatically closed 15 days after the last reply. New replies are no longer allowed.