Knowledge Hub / Networking

DNS

How does a name become usable network data?

Name resolution, records, caching, commands and the trust boundaries around DNS.

Last verified: 2026-09-20
Review interval: 365 days
Status: In review

01 / Overview

How does a name become usable network data?

DNS is a distributed naming system. A client asks a resolver for typed data associated with a name; the resolver may answer from cache or continue through authoritative DNS data. A successful answer is evidence about a DNS record, not proof that the destination service is safe.

Level: Intermediate
Units: 4
Estimated time: 114 min

What you will learn

Distinguish a DNS name, zone, server and typed record.
Trace a query from client to recursive resolver and authoritative answer.
Choose a DNS command for the observation you need.
Separate a DNS failure from later route, port, TLS or application failures.

Know first

IP addressing
Network interface
Client and server
Packet
Command

Learning materials

Labs: available
Embedded practice: available
Visuals: 3
Documents: 3

01DNS names, hierarchy and record types28 min
02DNS resolution, referrals and cache24 min
03DNS tools and Wireshark inspection32 min
04DNS troubleshooting and security boundaries30 min

Start topic →

02 / Learn

Learn

DNS names, hierarchy and record types
Build the vocabulary needed to read a DNS answer without confusing names, zones, servers and records.
Open lesson →
DNS resolution, referrals and cache
Trace a recursive lookup and learn where cache changes the path.
Open lesson →
DNS tools and Wireshark inspection
Use DNS commands deliberately and learn how to inspect a query and response in Wireshark.
Open lesson →
DNS troubleshooting and security boundaries
Diagnose failures one boundary at a time and distinguish DNSSEC, encrypted DNS and DNS abuse.
Open lesson →

03 / Concepts

Concepts

Domain namedns-domain-name: A sequence of labels located in the hierarchical DNS namespace.
Resolverdns-resolver: The component that obtains DNS information for a client, directly or through referrals.
Authoritative serverdns-authoritative-server: A name server with authoritative data for a zone rather than a cached copy from elsewhere.
Resource recorddns-resource-record: Typed DNS data associated with a name, such as an address or name-server record.
Cache and TTLdns-cache-ttl: Resolvers can reuse data for a bounded lifetime; TTL controls that cache interval.
Namespace and hierarchydns-namespace: DNS names form a tree: the root delegates top-level domains, which delegate zones below them.
Recursive resolutiondns-recursion: A recursive resolver follows referrals and returns a final answer or an error to its client.
Root and TLD serversdns-root-tld: Root and top-level-domain servers normally provide referrals toward the authoritative zone, not the host address itself.
A recorddns-record-a: Maps a name to an IPv4 address.
AAAA recorddns-record-aaaa: Maps a name to an IPv6 address.
CNAME recorddns-record-cname: Identifies one domain name as an alias of another canonical name.
MX recorddns-record-mx: Specifies mail exchangers for a domain with preference values.
TXT recorddns-record-txt: Carries one or more character strings; applications define how those strings are interpreted.
NS recorddns-record-ns: Identifies an authoritative name server for a zone.
PTR recorddns-record-ptr: Points from a name in the reverse namespace to another domain name.
SOA recorddns-record-soa: Carries administrative parameters for a zone, including its serial and timing values.

04 / Commands

Commands

Environment	Command	Purpose	Lab
multi	`nslookup example.test`	Ask a configured DNS server for information about a name.	Available in Command Lab
linux	`dig example.test A`	Inspect a DNS query and its returned sections with a query-oriented tool.	Available in Command Lab
powershell	`Resolve-DnsName example.test -Type A`	Resolve a name with the Windows DNS client cmdlet and request a record type explicitly.	Available in Command Lab
windows	`ipconfig /displaydns`	Display the contents of the Windows DNS client resolver cache.	Available in Command Lab
powershell	`Get-DnsClientCache`	Display entries in the Windows DNS client cache.	Available in Command Lab
powershell	`Clear-DnsClientCache`	Clear the Windows DNS client cache without producing success output.	Available in Command Lab
windows	`ipconfig /flushdns`	Flush the Windows DNS client resolver cache.	Available in Command Lab
linux	`host -t AAAA example.test`	Perform a compact DNS lookup for an explicitly selected record type.	Available in Command Lab
multi	`ping example.test`	Observe simulated name resolution followed by an ICMP reachability check; it does not prove application health.	Available in Command Lab

05 / Labs

Labs

DNS Command Lab
Guided DNS exercise for resolver, answer, record type and virtual cache state.
deterministic simulator
Open safe simulator →

06 / Visuals

Visuals

A sequence from application name to DNS resolver and returned address.
dns-resolution-flow
technical-diagram · verified
Open visual →
DNS hierarchy from the root through a top-level domain and authoritative zone to typed records.
dns-hierarchy-v1
technical-diagram · verified
Open visual →
Wireshark 4.6.8 on macOS showing a controlled DNS query and response filtered with dns, with packet list, details and bytes panes visible.
wireshark-dns-ui-v1
real-screenshot · verified
Open visual →

06B / Documents

Documents

DNS Foundations Study Guide
A project-authored guide to names, resolvers, records, caching, commands, troubleshooting and the boundaries of DNS security.
local PDF + HTML · project-owned
Open document →
RFC 1034 — Domain Names: Concepts and Facilities
The normative DNS concepts reference used to verify the platform's original explanations. It remains on the official RFC Editor site.
external reference only · external-only
Open document →
Wireshark User's Guide
The official current interface and workflow reference. The platform links to it instead of storing an unverified local copy.
external reference only · external-only
Open document →

07 / Security

Security

Treat DNS answers as data crossing a trust boundary. A resolver response can be wrong, stale or maliciously influenced.
DNSSEC authenticates signed DNS data; it does not encrypt the DNS question or make the destination application trustworthy.

08 / Troubleshooting

Troubleshooting

Separate the name, requested record type, resolver used, returned answer, cache state and the later connection attempt.
Compare answers from the configured resolver with an explicitly selected resolver before blaming the application.

09 / Quick checks

Quick checks

Level 2dns-resolver-vs-answer

A lookup shows Server: 192.0.2.53 and Address: 192.0.2.25. Which value identifies the DNS resolver used for the query?

192.0.2.53192.0.2.25

Level 4dns-reachability-diagnosis

A workstation can reach 192.0.2.25 but cannot resolve app.example.test. Which subsystem should you inspect first?

DNS resolutionLocal storageDisplay driver

Level 3dns-cache-flush-effect

What does Clear-DnsClientCache change in the DNS Command Lab?

The simulated local DNS client cacheThe authoritative zoneFiles on the learner's computer

Level 3wireshark-dns-display-filter

A capture already exists. Which Wireshark display filter shows decoded DNS protocol traffic?

dnscapture port 53

What does a resolver do that a browser normally does not do by itself?
Why does a valid DNS answer not prove that the destination service is safe?

10 / GRAPH

Related concepts

DHCP
TCP
UDP
ICMP →
HTTP
TLS
Wireshark
Linux shell →
PowerShell →

Used in certifications

These links reuse canonical knowledge; the certification page does not own or duplicate the topic.

11 / Resources

Resources

RFC 1034 — Domain Names: Concepts and Facilities
RFC Editor · official-doc · free
Resources ↗
RFC 1035 — Domain Names: Implementation and Specification
RFC Editor · official-doc · free
Resources ↗
RFC 4033 — DNS Security Introduction and Requirements
RFC Editor · official-doc · free
Resources ↗
RFC 8484 — DNS Queries over HTTPS
RFC Editor · official-doc · free
Resources ↗
nslookup command
Microsoft · official-doc · free
Resources ↗
ipconfig command
Microsoft · official-doc · free
Resources ↗
DnsClient PowerShell module
Microsoft · official-doc · free
Resources ↗
BIND 9.20 manual pages
Internet Systems Consortium · official-doc · free
Resources ↗
Wireshark User's Guide
Wireshark Foundation · official-doc · free
Resources ↗
Wireshark DNS display-filter reference
Wireshark Foundation · official-doc · free
Resources ↗

12 / Sources and freshness

Sources and freshness

Last verified: 2026-09-20
Review interval: 365 days
Source version: RFC 1034/1035/4033/8484 · BIND 9.20.29 · Wireshark User's Guide 4.7 · Microsoft Learn 2026-09-20