📖 ~1 min read
Table of contents
Symptom & Impact
Hostnames fail to resolve, breaking package downloads, API calls, and outbound connectivity.
Environment & Reproduction
Observed on servers using mixed DHCP, static networking, or custom resolver overrides.
Root Cause Analysis
Resolver chain misconfiguration or unreachable upstream nameserver causes intermittent lookup failures.
Quick Triage
Test direct IP reachability and compare dig results against configured DNS servers.
Step-by-Step Diagnosis
Inspect /etc/resolv.conf, systemd-resolved status, and NetworkManager DNS settings.
Solution – Primary Fix
Define reliable nameservers, align resolver ownership, and restart networking components cleanly.
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Solution – Alternative Approaches
Deploy a local caching resolver to reduce external DNS dependency and transient timeout impact.
Verification & Acceptance Criteria
Repeated dig and getent host lookups succeed with stable latency and no SERVFAIL spikes.
Rollback Plan
Revert resolver and network configs to previous validated versions and restart services.
Prevention & Hardening
Monitor DNS SLA, configure redundant resolvers, and enforce config management for resolver files.
Related Errors & Cross-Refs
Temporary failure resolving; Name or service not known; server misbehaving.
Related tutorial: View the step-by-step tutorial for debian-12.
View all debian-12 tutorials on the Tutorials Hub →
Browse all common problems & solutions on the Tutorials Hub.
References & Further Reading
systemd-resolved documentation, Debian networking manual, and DNS operations runbooks.
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