How to Fix Subdomains Not Resolving Due to Missing Root Indicator in DNS Zones Make it Rain Paper

Overview

When adding a subdomain in DNS management tools like WHM or external DNS panels, the subdomain may fail to resolve if the fully-qualified domain name (FQDN) is entered without a trailing period ("."). This occurs due to the way DNS zones are processed as relative by default.

Pre-requirements

• Access to your DNS Zone editor (e.g., WHM, cPanel, or external DNS panel)
• Basic knowledge of DNS records and subdomains
• Administrative rights to modify DNS settings

Understanding the Issue

DNS zones are relative, meaning if the "root" indicator (a trailing period) is not included when adding a subdomain, the DNS system may misinterpret the entry and append the domain name twice. For example:

sub.example_domain.com.domain.com

Instead of properly resolving the subdomain, it appends the domain name twice, causing a resolution failure.

Steps to Resolve the Subdomain Issue

Step 1: Open Your DNS Zone Editor

Access your DNS zone editor through WHM, cPanel, or an external DNS provider's management panel.

Step 2: Add the Subdomain

When adding a subdomain, ensure you enter either:

• Only the subdomain name (e.g., sub)
• The fully-qualified domain name with the trailing period (e.g., sub.example_domain.com.)

Step 3: Verify the Record

Ensure that the DNS record for the subdomain is correctly added. You can verify using the dig command:

dig sub.example_domain.com

If configured properly, you should receive a valid response with the correct IP address.

Common Mistakes to Avoid

• Do not enter the fully-qualified domain name (FQDN) without the trailing period ("."). If you use sub.example_domain.com without the period, it may append the domain again, resulting in a misconfiguration.
• Avoid only entering part of the domain like sub.example_domain, as it can lead to incomplete DNS records.

Gotchas to Avoid

• If using a third-party DNS provider, ensure that you are aware of how their system handles relative DNS entries. Some providers automatically add the domain name if the FQDN is not provided with a trailing period.
• Make sure the DNS changes have propagated. DNS propagation may take up to 48 hours to fully complete.

Additional Troubleshooting Tips

• Use nslookup or dig commands to verify DNS record propagation:

dig sub.example_domain.com

• Check for any conflicting DNS records or misconfigurations that might prevent the subdomain from resolving properly.

Additional Resources

• Understanding Domain Names and DNS Zones
• RFC 1034 - Domain Names: Concepts and Facilities