Ubuntu 24.04 LTS Intermittent DNS Failures 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

Name lookups randomly fail, breaking package installs, API calls, and internal service discovery.

Environment & Reproduction

Ubuntu 24.04 hosts using systemd-resolved stub resolver with mixed upstream DNS servers.

Root Cause Analysis

Unreliable upstream resolvers and timeout fallback behavior produce intermittent NXDOMAIN or SERVFAIL.

Quick Triage

Check resolver status and current upstream server health from the host perspective.

resolvectl status; ping -c 2 1.1.1.1

Step-by-Step Diagnosis

Test repeated queries, inspect per-link DNS, and review resolved logs for timeout spikes.

for i in {1..10}; do resolvectl query archive.ubuntu.com; done; sudo journalctl -u systemd-resolved --since '2 hours ago'

Solution – Primary Fix

Set stable DNS servers in netplan, apply configuration, and restart resolved for clean state.

sudoedit /etc/netplan/01-netcfg.yaml && sudo netplan apply && sudo systemctl restart systemd-resolved

Solution – Alternative Approaches

Deploy local caching resolver or conditional forwarding for split-horizon enterprise domains.

Verification & Acceptance Criteria

Repeated queries succeed with low latency and no resolver timeout bursts in logs.

Rollback Plan

Revert netplan DNS entries and restore previous nameserver set if new servers underperform.

Prevention & Hardening

Monitor resolver latency and automate alerts on sustained SERVFAIL/NXDOMAIN anomalies.

Related Errors & Cross-Refs

Related to network route flaps and VPN DNS leakage conditions.

Related tutorial: View the step-by-step tutorial for Ubuntu 24.04 LTS.

View all Ubuntu 24.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

systemd-resolved man pages and Ubuntu networking documentation.