Split-horizon DNS returns different answers depending on where the query is made. It is common in corporate networks, VPNs, and private cloud environments.

Useful dig commands

dig @10.0.0.53 app.internal.example.com A
dig @1.1.1.1 app.internal.example.com A

Troubleshooting checklist

  1. Compare a private resolver with a public resolver.
  2. Check whether the name is meant to be public.
  3. Avoid publishing internal hostnames unintentionally.
  4. Document which resolver should be authoritative for each environment.

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.”