Common DNS Errors & How To Fix Them

DNS issues can cause website downtime, slow browsing, or even complete service outages. This guide covers the most common DNS errors, their causes, and step-by-step solutions to resolve them.

1. DNS_PROBE_FINISHED_NXDOMAIN

Cause:

• The domain does not exist or there is a misconfiguration in DNS settings.

Solution:

• Verify the domain name for typos.

• Flush the DNS cache using:

  ipconfig /flushdns  (Windows)
  sudo systemd-resolve --flush-caches  (Linux)

• Restart your router and try a different DNS resolver (Google DNS: 8.8.8.8).

2. SERVFAIL (Server Failure)

Cause:

• The DNS server failed to complete the query.

Solution:

• Check if the authoritative DNS server is down.

• Verify DNSSEC settings and logs.

• Use an alternative resolver to check if the issue is server-specific.

3. REFUSED Error

Cause:

• The DNS server refused to process the query.

Solution:

• Check the DNS server’s configuration for restrictions.

• Verify firewall rules that may block DNS queries.

• Restart the DNS server service (systemctl restart bind9).

4. DNS Timeouts

Cause:

• The DNS query took too long to respond.

Solution:

• Check network connectivity and packet loss.

• Ensure that DNS servers are reachable and not overloaded.

• Increase the timeout value in DNS client settings.

5. Mismatch Between Primary and Secondary DNS Servers

Cause:

• The secondary server has outdated zone files.

Solution:

• Force a zone transfer (rndc reload).

• Check logs for errors in synchronization.

• Ensure that TSIG keys match if used for secure transfers.

6. Incorrect or Missing MX Records

Cause:

• Mail servers are not properly defined in DNS.

Solution:

• Ensure that the MX records are correctly set.

• Verify mail server connectivity using:

  nslookup -q=mx example.com

• Check SPF, DKIM, and DMARC records for email security.

7. Reverse DNS Lookup Failures

Cause:

• The PTR record is missing or misconfigured.

Solution:

• Verify the PTR record with:

  nslookup 192.0.2.1

• Ensure that the authoritative server has the correct reverse DNS entry.

• Update the reverse DNS records with the hosting provider.

8. Propagation Delays

Cause:

• DNS changes take time to propagate globally.

Solution:

• Check the TTL (Time-To-Live) values; lower it before making changes.

• Use online DNS propagation checkers.

• Be patient, as updates can take up to 48 hours.

Conclusion

DNS issues are common but can often be resolved with systematic troubleshooting. Keeping DNS configurations accurate and monitoring server logs can prevent frequent outages.