📖 ~1 min read
Table of contents
Symptom & Impact
Link speed/duplex drops after reboot and throughput degrades significantly.
Environment & Reproduction
Seen where manual ifconfig tuning was never persisted.
ifconfig Root Cause Analysis
Runtime media settings are ephemeral unless captured in startup config.
Quick Triage
Compare expected media profile with current live interface state.
sysrc ifconfig_Step-by-Step Diagnosis
Inspect rc.conf and local overrides for conflicting interface directives.
grep -R "ifconfig_" /etc/rc.conf*
Solution – Primary Fix
Persist desired media options in rc.conf and restart netif.
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sudo sysrc ifconfig_='inet / media 1000baseT mediaopt full-duplex' && sudo service netif restart 
Solution – Alternative Approaches
Prefer autonegotiation if switch policy and hardware support are stable.
Verification & Acceptance Criteria
Interface retains expected speed/duplex after reboot.
Rollback Plan
Remove forced media options and return to prior autonegotiation profile.
Prevention & Hardening
Document interface tuning centrally and audit drift regularly.
Related Errors & Cross-Refs
Related to NIC driver updates and switch-side forced speed mismatches.
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 network interface configuration manual.
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