🟠 High   ⏱ 5–30 min  Last verified: 19 May 2026
Affected versions: FreeBSD 12

📖 ~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

CARP VIP repeatedly switches master/backup state, causing intermittent service interruptions and packet loss.

Environment & Reproduction

During interface or switch maintenance, both nodes oscillate between MASTER and BACKUP unexpectedly.

Root Cause Analysis

Skew misconfiguration, packet filtering of CARP advertisements, and interface latency spikes often trigger flapping.

Quick Triage

Check ifconfig carp status, sysctl net.inet.carp settings, and capture protocol 112 traffic between peers.

Step-by-Step Diagnosis

Correlate state transitions with link events and advertisement intervals to isolate instability origin. image_ref=0

Illustrative mockup for freebsd-12 — terminal_or_shell
Inspecting CARP state transitions and interface status — Illustrative mockup — Progressive Robot

Solution – Primary Fix

Adjust advskew/advbase appropriately, ensure CARP protocol traffic is allowed, and stabilize interface settings. image_ref=1

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Illustrative mockup for freebsd-12 — log_or_config
Reviewing carp and network failover configuration — Illustrative mockup — Progressive Robot

Solution – Alternative Approaches

Use dedicated heartbeat VLANs and stricter switch QoS for failover control-plane traffic.

Verification & Acceptance Criteria

CARP roles remain stable under load and maintenance simulation, with deterministic failover and recovery behavior.

Rollback Plan

Restore previous CARP tunables and disable recent network policy changes if flapping persists.

Prevention & Hardening

Run periodic failover drills and monitor CARP state-change frequency with automated alert thresholds.

Commonly linked with ARP cache churn, duplicate VIP warnings, and split-brain style failover incidents.

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

See man carp, FreeBSD High Availability guidance, and PF interaction notes for CARP traffic.

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