Causes
This error indicates Cloudflare is unable to send requests to your server because its origin IP cannot resolve the A/AAAA or CNAME DNS record requested.
The common causes are :
- The origin host names (CNAMEs) in your Cloudflare Load Balancer default, region, and fallback pools are unresolvable.
- A missing DNS A record that mentions the origin IP address.
- A CNAME record in Cloudflare DNS points to an unresolvable external domain.
Fixes
Step 1: Uses A Fallback Pool
Use a fallback pool configured with an origin IP as a backup in case all other pools are unavailable (1st cause)
Step 2: Verify Cloudflare DNS
Verify that your Cloudflare DNS settings include an A record that points to a valid IP address. You can choose to edit existing A record or create a new one. (2nd Cause)
Step 3: Ensure Target Domain Can Be Resolved
Ensure that the target domain can be resolved by using command line tools as well as third-party tools to check DNS resolution, such as dig and nslookup. (3rd Cause)
- dig command
- dig subdomain.example.com
- dig +trace subdomain.example.com
- dig subdomain.example.com @1.1.1.1
- nslookup
- nslookup subdomain.example.com
nslookup subdomain.example.com 1.1.1.1
- nslookup subdomain.example.com
Step 4: Try An Online Services
You can try an online services, such as whatsmydns.net, to check for DNS resolution worldwide. Take note that a response other than a valid IP address (e.g., timeout, SERVFAIL, NXDOMAIN or NOERROR) most likely points to the source of your issue.