DNS Troubleshooting

July 16, 2026 ยท View on GitHub

Troubleshoot from delegation toward the final service. Do not change multiple layers at once.

Step 1: Confirm the Exact Name and Type

dig A www.example.dpdns.org

Check for spelling mistakes, an unintended duplicated suffix, and the wrong record type.

Step 2: Check Parent Delegation

dig +trace NS example.dpdns.org

The delegation should lead to the authoritative nameservers configured at the registration service.

Step 3: Check Every Authoritative Server

dig @ns1.dns-service.example SOA example.dpdns.org
dig @ns2.dns-service.example SOA example.dpdns.org

All authoritative servers should answer for the zone. If they return different serials or values for too long, the DNS service may not have synchronized the zone.

Step 4: Query the Record Directly

dig @ns1.dns-service.example A www.example.dpdns.org

If the direct answer is wrong, edit the authoritative zone. Waiting for propagation will not fix a wrong authoritative answer.

Step 5: Compare Recursive Answers

Query the normal resolver and, if needed, a second resolver chosen by the user or network administrator. Different cached values can be normal during a TTL transition.

Common Problems

NXDOMAIN

  • The hostname is misspelled.
  • The record was created in the wrong zone.
  • The DNS interface appended the zone twice.
  • A negative answer is still cached.

SERVFAIL

  • Delegated nameservers do not answer.
  • The zone is missing from an authoritative server.
  • A network path or firewall is blocking DNS.

Correct DNS, but the website does not open

DNS only locates the server. Check:

curl -I http://example.dpdns.org
curl -I https://example.dpdns.org

Then check the server process, firewall, virtual host, certificate, and application logs.

Only some users see the new website

  • Old DNS answers may still be cached.
  • IPv4 and IPv6 may point to different servers.
  • A proxy or application cache may hold old content.
  • The client may be using a different hostname.

www works but the root does not

Check the root A or AAAA record and the web server's accepted hostnames. A www CNAME does not automatically configure the root.

Collect Evidence Before Asking for Help

Include:

  • The exact hostname and record type
  • dig NS output
  • A direct authoritative query
  • The expected and actual value
  • The time of the change and previous TTL
  • HTTP status from curl -I, when relevant

Remove tokens, cookies, account IDs, private addresses, and unrelated personal data before sharing logs or screenshots.

Continue to Part 3: Build and Publish a Website.