RHEL 9: 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 sometimes resolve and sometimes fail, affecting package installs and app dependencies.

Environment & Reproduction

Run `resolvectl status`, `dig`, and `nmcli connection show` for DNS assignment details.

Root Cause Analysis

Verify resolver-related packages and NSS components are installed correctly.

Quick Triage

Check `systemctl status NetworkManager` and any local caching resolver service.

Step-by-Step Diagnosis

Review `journalctl -b -u NetworkManager` for DHCP DNS churn and resolver updates.

Solution – Primary Fix

Set static DNS via `nmcli connection modify` and reconnect profile to apply.

Solution – Alternative Approaches

Confirm outbound UDP/TCP 53 is not blocked by `firewalld` or upstream ACLs.

Verification & Acceptance Criteria

SELinux generally allows resolver operations; audit only if custom local DNS service is denied.

Rollback Plan

Reboot and validate stable resolution with repeated `dig` tests.

Prevention & Hardening

Avoid conflicting DNS settings from multiple network profiles.

Related Errors & Cross-Refs

Restore previous connection profile from backup if static settings break failover.

Related tutorial: View the step-by-step tutorial for rhel-9.

View all rhel-9 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Use NetworkManager and resolver documentation for enterprise DNS design.