A subdomain can fail even when the root domain works. It may need its own A, AAAA, CNAME, TXT, or service-specific record.

Useful dig commands

dig app.example.com A
dig app.example.com CNAME
dig app.example.com TXT

Troubleshooting checklist

  1. Check the exact subdomain.
  2. Check whether the service expects CNAME or A records.
  3. Check for conflicting CNAME and other records.
  4. Check the parent domain delegation if nothing resolves.

How to interpret the result

If the answer matches the expected value, DNS is probably not the layer causing the current symptom. Continue with HTTP, TLS, mail server, firewall, or application checks. If the answer is missing, stale, or different between resolvers, keep the investigation in DNS until the public answer is correct.

Support note

When opening a ticket with a DNS provider, include the exact name, record type, resolver tested, returned value, and time of the lookup. That is much more useful than saying “DNS is not working.”