DNS
Name resolution roles, common record types, iterative and recursive queries, and basic verification of client and device DNS.
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.
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.) |
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.
Server: 192.168.10.53Which resolver answered — verify it's the one you configured.Address: 192.168.10.53#53Non-authoritative answer:Came from a resolver, not the zone owner — could be cached or freshly resolved recursively.Name: example.comAddress: 93.184.216.34The A record returned.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.