🟠 High   ⏱ 5–30 min  Last verified: 19 May 2026
Affected versions: FreeBSD 15

📖 ~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

Failover VIP never becomes master, causing service downtime on primary failure.

Environment & Reproduction

Usually appears after config drift across cluster peers.

ifconfig carp0

Root Cause Analysis

Advertisement timing, VHID, passphrase, or skew mismatch blocks master election.

Quick Triage

Compare CARP settings on all nodes and inspect packet exchange.

tcpdump -ni  proto carp

Step-by-Step Diagnosis

Verify shared VHID/password and ensure no duplicate virtual host IDs.

sysctl net.inet.carp
Illustrative mockup for freebsd-15 — carp_status
CARP remains in BACKUP unexpectedly — Illustrative mockup — Progressive Robot

Solution – Primary Fix

Align CARP parameters and enable preempt where required.

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sudo sysrc ifconfig_carp0='vhid 1 pass  advskew 0' && sudo service netif restart
Illustrative mockup for freebsd-15 — carp_advskew_fix
Adjusting advskew and preempt settings — Illustrative mockup — Progressive Robot

Solution – Alternative Approaches

Use maintenance demotion scripts during patch windows to control role changes.

Verification & Acceptance Criteria

Expected node transitions to MASTER and failover tests succeed.

Rollback Plan

Restore previous CARP parameters and clear temporary demotion values.

Prevention & Hardening

Track HA config via source control and drift detection.

Related to blocked multicast and mismatched interface MTU settings.

Related tutorial: View the step-by-step tutorial for freebsd-15.

View all freebsd-15 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

FreeBSD CARP design and operational guidance.

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