dns-resolution-diagnosis

Diagnosing DNS resolution failures requires analyzing system configurations, network connectivity, and protocol-level responses. You must check for local misconfigurations, systemd-resolved cache issues, or upstream firewalls blocking UDP port 53.

Intermittent domain resolution timeouts are frequently caused by configuration inconsistencies, cache pollution, or network-level blocking. Investigate whether the root cause is a local resolv.conf error, a systemd-resolved cache issue, or upstream firewalls.

Troubleshooting a systemd-resolved cache issue requires a multi-layer root cause analysis across system configuration and protocol types. This approach identifies whether failures are due to cache pollution, TCP fallback issues, or EDNS0 incompatibility.

Yes, using dig and resolvectl enables multi-layer root cause analysis for DNS hijacking. These tools analyze protocol-level responses and system configurations to detect network-level blocking, EDNS0 incompatibility, and configuration inconsistencies.

Yes, tcpdump and iptables are required to diagnose upstream firewall blocking UDP 53. These network diagnostic tools capture protocol-level traffic and inspect rules to identify network-level blocking causing domain lookup timeouts.

Automated troubleshooting for TCP fallback issues is limited to detecting known failure modes like EDNS0 incompatibility and configuration inconsistencies. It requires standard network diagnostic tools and cannot fix external upstream firewall policies blocking traffic.