Why a Wildcard Record Does Not Resolve an Empty Non-Terminal Hostname

This article explains how to check whether a hostname is an empty non-terminal and why a wildcard record may not answer for that hostname.

Overview

A wildcard DNS record, such as *.domain.com, can answer for hostnames that do not already exist in the zone. 

However, wildcard matching does not apply when the queried hostname already exists as an empty non-terminal.

An empty non-terminal is a hostname that does not have its own DNS record, but has one or more child records below it.

Example

If the zone contains qa.example.domain.com, then example.domain.com exists in the DNS tree because it has a child record below it.

If example.domain.com does not have its own DNS record, it is an empty non-terminal. 

In that case, a wildcard record such as *.domain.com will not provide an answer for example.domain.com.

How to Check for an Empty Non-Terminal

1. Log in to UltraDNS.
2. Click Domains.
3. Open the domain that contains the wildcard record.
4. Search for *.domain.com.
5. Confirm that a wildcard record exists for *.domain.com.
6. Search for the hostname that is not resolving, such as example.domain.com.
7. Review the results:
   • If records exist below the hostname, such as qa.example.domain.com, then example.domain.com is an empty non-terminal.
   • If no records exist below the hostname, then the source material does not establish that the hostname is an empty non-terminal.

How to Resolve the Issue

If the hostname is an empty non-terminal, create a specific DNS record for that hostname.

For example, if example.domain.com must resolve, create the required record directly at example.domain.com instead of relying on *.domain.com.

Expected Outcome

After a specific record is created for the empty non-terminal hostname, DNS queries for that hostname can return the configured record instead of relying on the wildcard record.

Important Notes

• A wildcard record does not override an existing name in the DNS tree.
• A hostname can exist in the DNS tree even when it does not have a record directly assigned to it.
• Empty non-terminal behavior is defined in DNS standards. For more information, review RFC 5155.