Why Subdomains Fail While the Main Domain Works

 


It’s a scenario many website owners encounter:

  • The main domain works perfectly,

  • but subdomains are failing to load or resolve.

While this may seem puzzling, the issue usually stems from DNS misconfigurations or missing records for the subdomain. Subdomains are not automatically linked to the main domain's DNS settings; they require explicit DNS records to function correctly.

In this guide, we’ll explore why subdomains fail while the main domain works and provide actionable steps for troubleshooting and resolving the issue.


Why Subdomains Require Independent DNS Records

Subdomains Aren’t Automatically Linked to the Main Domain

A common misunderstanding is that subdomains inherit all settings from the main domain.
However, subdomains are treated as separate entities in DNS. This means they require their own records (such as A, CNAME, MX) to function properly.


If the required DNS records for a subdomain are missing or incorrectly configured, it won’t resolve even if the main domain works fine.

Common Causes of Subdomain Failures

  • Missing A or CNAME records for the subdomain

  • Incorrectly configured DNS settings for the subdomain

  • Incorrect or missing delegation of DNS authority (e.g., for large domains with multiple subdomains)



Common DNS Record Errors That Cause Subdomain Failures

1. Missing or Incorrect DNS Records

If your subdomain doesn't have a corresponding DNS record, or the record is misconfigured, it will fail to resolve. Here are common DNS record issues:

A Record: Points the subdomain to an IP address (e.g., subdomain.example.com → 192.0.2.1).

CNAME Record: Points the subdomain to another domain (e.g., subdomain.example.com → example.com).

If these records are missing or incorrect, DNS queries will not return the correct IP address, causing your subdomain to fail.


2. Incorrect Formatting

Subdomain records need to be correctly formatted. For instance, an extra domain part like: trial.example.com.example.com is incorrect.

The correct entry should only include the subdomain: trial.example.com 

Formatting errors can prevent DNS servers from finding the correct record.



Subdomain Delegation: When a Subdomain Requires Independent DNS Hosting

In some cases, a subdomain needs to be hosted on a separate DNS provider or delegated to another set of DNS records.

For example, if you have a subdomain sub.example.com and want it managed by a different DNS service, the parent domain (example.com) must have an NS (Nameserver) record pointing to the correct DNS provider for the subdomain.

If this step is missed, the subdomain will not resolve properly.



DNS Propagation and Caching Delays

Even after DNS records are correctly configured for the subdomain, DNS propagation may delay its resolution.

Why DNS Propagation Matters:

  • DNS changes are not instantaneous.

  • Local DNS resolvers may cache old records for a period (TTL — Time to Live).
  • Some users may see the updated DNS records, while others still get cached results.

During propagation, it’s common for the main domain to be fully functional while the subdomain still faces issues.



Common Misunderstandings About Subdomains

Misunderstanding 1: "The main domain works, so the subdomain should too"

While it may seem like the subdomain should automatically work if the main domain is functioning, this is not the case. Subdomains require explicit DNS records and may have separate settings that need to be configured.

Misunderstanding 2: "Subdomains automatically inherit settings from the main domain"

Subdomains are essentially separate entities in DNS. They don’t automatically inherit settings or records from the main domain unless explicitly defined.

Misunderstanding 3: "Changing DNS settings for the main domain also updates the subdomain"

Changing settings for the main domain will not automatically affect subdomains. You must manually update or configure the subdomain’s DNS records.



Steps to Troubleshoot Subdomain Issues

To resolve subdomain issues, follow this checklist:

Check DNS Records for the Subdomain: Use a DNS lookup tool (like dig or nslookup) to verify that the subdomain’s DNS records exist and are correct.

Verify Record Type: Ensure that the record type (A, CNAME, etc.) matches the subdomain’s requirements.

Confirm the Record Is Added to the Right Domain: Double-check that the record is added to the correct DNS zone (parent domain or subdomain).

Wait for DNS Propagation: If changes have been made recently, allow sufficient time for DNS propagation to take effect.

By following this process, you can quickly identify where the issue lies and avoid unnecessary troubleshooting.


Conclusion

DNS issues related to subdomains are often the result of missing or misconfigured DNS records. Unlike main domains, subdomains require explicit records to function properly. By understanding the roles of DNS records, subdomain delegation, and DNS propagation, you can efficiently troubleshoot and resolve subdomain issues without unnecessary support requests.

Nicenic helps customers navigate DNS and domain management, ensuring smooth operations for both primary domains and subdomains. As an ICANN-accredited registrar, we support businesses in managing DNS configurations and ensuring reliability across the web.


Nicenic stands as that trusted partner for brands, developers, entrepreneurs, and businesses worldwide.

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