How to Diagnose Linux Server DNS Resolution Issues

Episode 55 of Linux Server Admin tackles a common but infuriating problem: DNS resolution failures that can cripple server connectivity. Lucas and Luna walk through a real-world scenario where an application suddenly can't reach external APIs. They cover the diagnostic toolkit — digging into /etc/resolv.conf, testing with dig and nslookup, checking systemd-resolved stubs, and tracing timeouts with tcpdump. Specific commands like 'dig +trace example.com' and 'resolvectl query' are demonstrated. They also discuss how stub resolvers can mask upstream failures and when to use fallback nameservers. By the end, you'll have a repeatable process for isolating whether the problem is a misconfigured resolver, a blocked port, or a slow upstream server. No fluff — just practical server troubleshooting for sysadmins.

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