Ubuntu 18.04 intermittent DNS resolution failures

📖 ~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

Hostnames intermittently fail to resolve, disrupting browsing and package updates.

Environment & Reproduction

Ping by IP succeeds while domain lookups randomly fail.

Root Cause Analysis

Resolver misconfiguration, unstable upstream DNS, or network manager race conditions can cause failures.

Quick Triage

Test lookup against multiple resolvers and verify current nameserver settings.

Step-by-Step Diagnosis

Use resolvectl or systemd-resolve stats, dig queries, and inspect /etc/resolv.conf links.

Solution – Primary Fix

Set reliable DNS servers, correct resolver service ownership, and flush caches.

Solution – Alternative Approaches

Deploy local caching resolver for consistency in unreliable upstream environments.

Verification & Acceptance Criteria

Repeated DNS queries succeed with low latency and no random NXDOMAIN/timeouts.

Rollback Plan

Restore prior resolver settings if application-specific DNS routes break.

Prevention & Hardening

Monitor DNS health and define resilient primary/secondary resolvers.

Related Errors & Cross-Refs

Often surfaces with apt fetch errors and VPN split-DNS conflicts.

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

Review systemd-resolved and Ubuntu name resolution architecture docs.