Ubuntu 18.04 LTS DNS resolution fails intermittently with systemd-resolved

📖 ~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

Applications fail to resolve domains causing service disruptions.

Environment & Reproduction

Ubuntu 18.04 with Netplan and mixed DHCP or static DNS settings.

Root Cause Analysis

Resolver race conditions and stale upstream entries cause lookup failures.

Quick Triage

Test direct IP connectivity and compare dig versus ping behavior.

Step-by-Step Diagnosis

Inspect resolvectl status, journal logs, and /etc/resolv.conf linkage.

Solution – Primary Fix

Set consistent upstream servers and restart systemd-resolved cleanly.

Solution – Alternative Approaches

Switch to NetworkManager DNS handling for desktop-heavy systems.

Verification & Acceptance Criteria

Repeated lookups complete quickly with no timeout or SERVFAIL.

Rollback Plan

Restore previous Netplan YAML and resolver symlink configuration.

Prevention & Hardening

Pin trusted resolvers and monitor DNS latency over time.

Related Errors & Cross-Refs

Cross-check against firewall egress blocks and proxy misconfiguration.

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 manuals and Ubuntu networking reference guides.