FreeBSD 12 – resolv.conf gets overwritten by dhclient and breaks internal DNS

📖 ~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 DNS resolution intermittently fails after lease renew events.

Environment & Reproduction

Seen in mixed static/DHCP networks requiring custom resolvers.

Root Cause Analysis

dhclient rewrites resolv.conf, dropping enterprise DNS settings.

Quick Triage

Compare file timestamps with dhclient renewal log entries.

Step-by-Step Diagnosis

Review dhclient.conf and lease options controlling resolver updates.

Solution – Primary Fix

Use supersede directives to preserve required DNS servers/search domains.

Solution – Alternative Approaches

Set static interface and resolver configuration on critical hosts.

Verification & Acceptance Criteria

Renewal no longer removes internal resolver entries.

Rollback Plan

Remove supersede lines and revert to provider DNS behavior.

Prevention & Hardening

Monitor resolv.conf checksum changes and alert on drift.

Related Errors & Cross-Refs

Common with split-DNS VPN and search-order issues.

Related tutorial: View the step-by-step tutorial for FreeBSD 12.

View all FreeBSD 12 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

dhclient.conf manual and FreeBSD netif configuration docs.