📖 ~1 min read
Table of contents
Symptom & Impact
Hosts can resolve names but outbound traffic intermittently times out.
Environment & Reproduction
Common on dual-stack networks with inconsistent router advertisements.
Root Cause Analysis
Kernel prefers an invalid or low-quality IPv6 default route.
Quick Triage
Inspect active IPv6 routes and source address selection.
Step-by-Step Diagnosis
Capture RA behavior and route changes over time.
Solution – Primary Fix
Adjust RA acceptance and route metrics for stable egress.
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Solution – Alternative Approaches
Temporarily disable IPv6 on affected interface until upstream routing is corrected.
Verification & Acceptance Criteria
IPv6 traceroute and external connectivity tests pass consistently.
Rollback Plan
Revert sysctl and route metric changes if policy requires original behavior.
Prevention & Hardening
Standardize RA policy and validate dual-stack routing in staging.
Related Errors & Cross-Refs
Related to PMTU blackholes and asymmetric upstream routes.
Related tutorial: View the step-by-step tutorial for Debian 13.
View all Debian 13 tutorials on the Tutorials Hub →
Browse all common problems & solutions on the Tutorials Hub.
References & Further Reading
Debian IPv6 networking and route policy references.
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