CCNA 200-301 v1.1 reference — IP Services

DNS

Name resolution roles, common record types, iterative and recursive queries, and basic verification of client and device DNS.

Objective 4.3v1.1 exam target

Quick Reference Handbook

How resolution works

DNS resolves names to addresses (and more) — hierarchical, distributed, cached. A client asks a recursive resolver which walks root → TLD → authoritative servers (iterative queries) and returns the answer. UDP 53 for normal queries; TCP 53 for zone transfers and oversized responses.

Roles to keep straight: the stub resolver on the client asks; the recursive resolver (usually the ISP/enterprise server) hunts the answer down; authoritative servers own zones; root and TLD servers only refer you onward. Caching at every level is bounded by each record's TTL.

Trace a first-time lookup

Client asks: www.example.org

Stub → recursive resolver: 'give me the answer'.
Resolver → root: referral to .org TLD servers.
Resolver → .org TLD: referral to example.org's authoritative NS.
Resolver → authoritative NS: the A record → cached and returned to the client.

The client sees one query/answer; the resolver did the walking.

Record types

Common DNS record types

Type	Purpose
A	Name → IPv4 address
AAAA	Name → IPv6 address
CNAME	Name → another name (alias)
MX	Mail exchangers for a domain
PTR	IP → name (reverse lookup)
NS	Authoritative name servers for a zone
TXT	Arbitrary text (verification, SPF, etc.)

Configuration and verification

Configure device DNS resolution

Let the router resolve names — Privileged EXEC → Global configuration

Cisco IOS / IOS XE

configure terminal
ip name-server 192.168.10.53
ip domain-name example.test
ip domain lookup
 end

Verify

show hosts
ping router1.example.test

Name lookups succeed and cache in show hosts.
Typos at the CLI trigger a lookup attempt when domain lookup is on — disable it on lab gear to avoid the delay.

Changes device configuration.

$ nslookup example.com (interpreted)

Server: 192.168.10.53Which resolver answered — verify it's the one you configured.

Address: 192.168.10.53#53

Non-authoritative answer:Came from a resolver, not the zone owner — could be cached or freshly resolved recursively.

Name: example.com

Address: 93.184.216.34The A record returned.

Common mistakes

Treating 'NXDOMAIN' as a network failure — it is a valid DNS answer: the name does not exist.
Forgetting TCP/53 — large responses and transfers use TCP; opening only UDP breaks them.
Blaming DNS when the resolver itself is unreachable — test the resolver IP first.
Confusing recursive vs iterative — resolvers do recursive work for clients and iterative work among servers.

Everything fails by name, works by IP

Observation: All name lookups time out on one subnet; other subnets are fine.

Hypotheses

Clients' DNS server address wrong/missing on this scope
ACL between this subnet and the resolver
Resolver down for everyone (ruled out — others work)

Check	Indicates
`ipconfig /all` (or OS equivalent) DNS field	Confirms the assigned resolver for this subnet.
Ping the resolver IP from the subnet	Reachability vs DNS-service failure split.
`nslookup host <server-ip>` explicitly	Bypasses the configured server to isolate the path.

Correction: Fix the DHCP-delivered DNS option or the ACL.

Lookups succeed against the configured resolver.

On this page

How resolution works
Record types
Configuration and verification

Related resources

Practise this topic Source topic 38: DNS (Domain Name System)Practise topic 38 deck

Sources

Cisco CCNA 200-301 v1.1 Exam Topics (official PDF) — reviewed 2026-11-02
RFC 1034 — Domain Names — Concepts and Facilities — reviewed 2026-11-02
RFC 1035 — Domain Names — Implementation and Specification — reviewed 2026-11-02

Targets CCNA 200-301 v1.1 objectives. Supplemental blocks are labeled beyond exam scope.