NETWORKING
DNS Explained for IT Technicians
Learn what DNS does, what a lookup failure looks like, and how to separate DNS trouble from general network trouble.
Updated 28 October 2026 · Original TechLoomix learning examples. Fictional cases are labeled; no production changes are required.
Start with the question DNS actually answers
DNS returns records for names. An address record, a mail-routing record and a name-server record answer different questions. A successful lookup does not prove that a web application is healthy: the service can still fail because of routing, TLS, authentication or its own backend. Write down the exact name and record type before diagnosing “the internet.”
Worked case: one internal site fails
In this fictional lab, a laptop opens public websites but cannot open portal.example.test. A colleague on the same approved network can open it. First compare the complete hostname and the configured DNS server. Record a lookup against the laptop’s configured resolver, then compare the colleague’s answer. If one machine uses an unintended resolver, investigate how that setting was assigned. Do not replace corporate DNS with a public resolver; private zones may be unavailable there.
An NXDOMAIN answer means the queried name was reported nonexistent by that DNS path. A timeout means no timely response; it does not establish that the record is absent. An old address can suggest caching, but confirm the intended record before clearing anything.
A small evidence table
- Query: exact fully qualified hostname and record type.
- Resolver: address used, network/VPN context and time.
- Response: returned address, error or timeout.
- Comparison: one working client with the same intended access.
- Outcome: verified application access or a precise escalation.
Practice without changing production
Create three paper tickets: the correct name returns an unexpected address; the correct name times out; and a misspelled name returns nonexistent. For each, write one next observation that would distinguish two possible causes. A strong answer explains what the test can establish and what it cannot. Never use an IP-only browser test as proof that HTTPS should work: certificate names and virtual hosting matter.
Technical references
Continue with a practical exercise
Download the free readiness checklist or browse the learning library. Use the next resource to answer one specific gap in your evidence.