Ubuntu 18.04 DNS Resolution Fails Intermittently

📖 ~1 min read

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

Internet connectivity exists but hostnames fail to resolve reliably.

Environment & Reproduction

Occurs on DHCP networks using systemd-resolved with changing upstream DNS.

Root Cause Analysis

Resolver misconfiguration, stale cache, or conflicting network manager profiles.

Quick Triage

Compare ping by IP versus hostname and test current DNS server responses.

Step-by-Step Diagnosis

Review resolvectl status, /etc/resolv.conf link, and NetworkManager DNS settings.

Solution – Primary Fix

Set reliable DNS servers, restart resolved and NetworkManager, then flush DNS cache.

Solution – Alternative Approaches

Use local caching resolver or static netplan DNS entries for consistency.

Verification & Acceptance Criteria

Repeated lookup tests succeed across reboot and network reconnect cycles.

Rollback Plan

Restore previous netplan profile if custom resolver changes disrupt routing.

Prevention & Hardening

Standardize DNS profiles and monitor resolver latency from endpoints.

Related Errors & Cross-Refs

Temporary failure in name resolution, SERVFAIL responses, intermittent NXDOMAIN.

Related tutorial: View the step-by-step tutorial for Ubuntu 18.04 LTS.

View all Ubuntu 18.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

systemd-resolved, netplan, and NetworkManager DNS documentation.