When trying to setup Cloudflare DNS for SSL for my DigitalOcean Ubuntu server, I received a “Error 521” and started troubleshooting.
I found this article: https://support.cloudflare.com/hc/en-us/articles/200169166-How-do-I-whitelist-CloudFlare-s-IP-addresses-in-iptables-
And followed the steps until saving. Since there was no change, when I tested https://MyDomain.com, I didn’t bother saving the iptable entries.
Is there something I’m missing here??
This textbox defaults to using Markdown to format your answer.
You can type !ref in this text area to quickly search our full set of tutorials, documentation & marketplace offerings and insert the link!
Accepted Answer
MDS nailed it in the comment section, essentially when your are getting a 521 error on SSL requests, but non-SSL requests work fine; it usually indicates one of two things:
- Your web server is not set-up to receive SSL connections.
- Your firewall is blocking connections over SSL.
This behaviour can occur in Full and Full (Strict) mode, but not Flexible as the connection will be in plain-text HTTP.
If your web server is not configured to receive SSL connections, you will need to add this configuration before using Full or Full (Strict), however if it is configured you will instead need to whitelist port 443 on your server.
In IP Tables it is possible to open up port 443 as follows:
iptables -A INPUT -p tcp -m tcp --dport 443 -j ACCEPT
The next step would be to whitelist CloudFlare’s IPs, there is a guide on how to whitelist CloudFlare IPs in IPTables.
Hello there,
Also, another thing to mention is that you’ll need to make sure all CloudFlare’s IP ranges.
A full list of IPs can be found here:
https://www.cloudflare.com/ips/
Regards
Become a contributor for community
Get paid to write technical tutorials and select a tech-focused charity to receive a matching donation.
DigitalOcean Documentation
Full documentation for every DigitalOcean product.
Resources for startups and SMBs
The Wave has everything you need to know about building a business, from raising funding to marketing your product.
The developer cloud
Scale up as you grow — whether you're running one virtual machine or ten thousand.
Get started for free
Sign up and get $200 in credit for your first 60 days with DigitalOcean.*
*This promotional offer applies to new accounts only.