RHEL 8 DNS Settings Overwritten by DHCP and Break Internal Name Resolution

📖 ~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

Internal service hostnames fail intermittently on RHEL 8 because DHCP lease renewals overwrite resolver settings with public or incorrect DNS servers.

Environment & Reproduction

Occurs on DHCP-managed interfaces where NetworkManager accepts peer DNS unintentionally. Reproduce by renewing leases and checking resolver changes.

Root Cause Analysis

Connection profile permits automatic DNS injection, replacing required internal resolvers. Split-horizon DNS architectures then break application lookups.

Quick Triage

Review nmcli connection show values, inspect /etc/resolv.conf, test lookups, and check systemctl status NetworkManager with journalctl logs around lease events.

Step-by-Step Diagnosis

Identify active profile, verify ipv4.ignore-auto-dns and static DNS parameters, and correlate lease renewal timestamps with observed resolution failures.

Solution – Primary Fix

Configure NetworkManager profile to ignore auto DNS, set approved internal resolvers, reactivate connection, and validate name resolution for critical domains.

Solution – Alternative Approaches

Use local DNS cache forwarding to internal resolvers, lock resolver config in immutable images, or segregate management/application interfaces by policy.

Verification & Acceptance Criteria

Resolver settings persist across renewals and reboot, critical FQDN lookups succeed, and dependent services recover without manual intervention.

Rollback Plan

Restore previous profile values, reactivate connection, and revert to DHCP-provided DNS temporarily if emergency connectivity requires it.

Prevention & Hardening

Template NetworkManager DNS policy, monitor resolver drift, and include DNS persistence checks in host compliance baselines.

Related Errors & Cross-Refs

Related to SSH reverse DNS delays, podman DNS failures, and subscription-manager repo access issues caused by resolver misconfiguration.

Related tutorial: View the step-by-step tutorial for rhel-8.

View all rhel-8 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Red Hat NetworkManager DNS documentation, nmcli man page, resolver behavior references, and journalctl guidance for network event troubleshooting.