📖 ~1 min read
Table of contents
Symptom & Impact
Host boots with wrong addressing, causing loss of route reachability and failed service registration.
Environment & Reproduction
Happens with YAML syntax errors, renderer mismatch, or cloud-init overwriting local netplan files.
Root Cause Analysis
Invalid or superseded netplan definitions are skipped, so runtime network config remains stale.
Quick Triage
Run netplan validation, identify effective renderer, and inspect cloud-init network ownership status.
Step-by-Step Diagnosis
Check YAML parse output, systemd-networkd logs, and file precedence under /etc/netplan.
Solution – Primary Fix
Correct YAML schema, disable conflicting cloud-init network management, and apply netplan persistently.
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Solution – Alternative Approaches
Use NetworkManager renderer where appropriate or static systemd-networkd unit definitions.
Verification & Acceptance Criteria
Assigned IP, routes, and DNS match intended design across reboot and interface restarts.
Rollback Plan
Restore prior netplan and cloud-init files if updated network model breaks production reachability.
Prevention & Hardening
Lint netplan YAML in CI and enforce one configuration owner for each host profile.
Related Errors & Cross-Refs
Cross-link to missing NIC and DNS instability cases with relevant Ubuntu networking tutorial.
Related tutorial: View the step-by-step tutorial for Ubuntu 18.04 LTS.
View all Ubuntu 18.04 LTS tutorials on the Tutorials Hub →
Browse all common problems & solutions on the Tutorials Hub.
References & Further Reading
Consult netplan reference docs, cloud-init networking docs, and Ubuntu server network guides.
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