📖 ~1 min read
Table of contents
Symptom & Impact
Applications intermittently fail DNS lookups, causing service outages and failed outbound API calls.
Environment & Reproduction
Debian 13 servers using systemd-resolved with mixed DHCP and static DNS configuration.
Root Cause Analysis
Inconsistent resolver upstreams and stale cache state can produce transient lookup failures.
Quick Triage
Validate /etc/resolv.conf linkage and current resolved status before changing network stacks.
Step-by-Step Diagnosis
Review resolver logs, query latency, and upstream reachability per interface.
Solution – Primary Fix
Normalize DNS settings, restart systemd-resolved, and flush local cache to clear stale records.
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Solution – Alternative Approaches
Use unbound or dnsmasq as a local caching resolver where explicit policy control is required.
Verification & Acceptance Criteria
Repeated dig/getent lookups succeed with stable response times and no SERVFAIL spikes.
Rollback Plan
Restore previous resolver configuration and restart network services to return to baseline behavior.
Prevention & Hardening
Pin reliable upstream resolvers and monitor DNS latency and failure rates as SLO indicators.
Related Errors & Cross-Refs
Related issues include split-DNS misrouting, stale DHCP leases, and broken search domain logic.
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 resolver documentation and systemd-resolved operational recommendations.
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