DNS: understand and diagnose resolution

Objectives and progression

This path starts with the chain linking application, resolver, and authority. It develops record-type interpretation, migration cache management, and response diagnosis before covering transport and validation. Cases use illustrative names and addresses, with support, private-network, and production decisions. The goal is evidence-based investigation and mitigation rather than random changes.

Audience: Production support, administrators, developers, and technical managers investigating connectivity.

Prerequisites: Understand IP addresses and terminal use; access only authorized exercise environments.

125 estimated study minutes

• Distinguish cache, authority, and client context.
• Interpret responses and choose the next diagnostic test.
• Plan changes and mitigation considering caching, transport, and validation.

Modules

1. Resolver, authority, and client context
2. Records, aliases, and query type
3. TTL, negative caching, and controlled change
4. NXDOMAIN, NODATA, SERVFAIL, and timeout
5. DNS transport and DNSSEC validation

Continue learning

Technical assessments

• TCP/IP
• TLS and Certificates
• Production Support L3

References and version

DNS RFC 1034/1035 with RFC 2181, 2308, 3596, 4033, 7766 and 8767; dig BIND 9.20

• RFC 3596: DNS IPv6 extensions · 2026-09-28
• RFC 1034: DNS concepts · 2026-09-28
• RFC 1035: DNS implementation · 2026-09-28
• RFC 2308: negative caching · 2026-09-28
• RFC 2181: DNS clarifications · 2026-09-28
• RFC 7766: DNS over TCP · 2026-09-28
• RFC 4033: DNS security · 2026-09-28
• RFC 8767: serving stale DNS data · 2026-09-28
• ISC BIND 9: dig manual · 2026-09-28