IPv6 Router Advertisement Instability

📖 ~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

IPv6 connectivity drops intermittently and default route disappears.

Environment & Reproduction

Unstable RAs, conflicting static routes, or interface reconfiguration races.

Root Cause Analysis

Use netstat -rn -f inet6 and rtsold status to observe route churn.

Quick Triage

Stabilize interface config and temporarily set static IPv6 gateway if appropriate.

Step-by-Step Diagnosis

Run ifconfig and netstat -rn -f inet6 repeatedly to capture flap timing.

Solution – Primary Fix

Inspect /etc/rc.conf for ifconfig_*_ipv6 and rtsold_enable inconsistencies.

Solution – Alternative Approaches

Choose either RA-driven or static model, apply with sysrc, and restart netif/routing.

Verification & Acceptance Criteria

Confirm stable IPv6 default route and successful external IPv6 reachability tests.

Rollback Plan

Avoid mixed dynamic/static IPv6 configuration on the same interface.

Prevention & Hardening

Revert to prior network profile and disable experimental IPv6 toggles.

Related Errors & Cross-Refs

Escalate if upstream router advertisements are malformed or inconsistent.

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

sysrc rtsold_enable=”YES”; service netif restart; service routing restart; netstat -rn -f inet6