What is DNS and what are the common DNS record types?
DNS maps names to addresses; key record types are A (IPv4), AAAA (IPv6), NS (name server), and MX (mail), and every DNS message has question, answer, authority, and additional sections.
DNS (Domain Name Service):
An automated service that matches resource names (like domain names) with their numeric IP addresses.
* A maps to IPv4, AAAA to IPv6, NS names the authoritative server, MX routes mail. *
Purpose: Domain names like www.cisco.com are much easier to remember than IP addresses like 198.133.219.25.
Common DNS Record Types:
| Record | Purpose |
|---|---|
| A | End device IPv4 address |
| NS | Authoritative name server |
| AAAA | End device IPv6 address (pronounced "quad-A") |
| MX | Mail exchange record |
DNS Message Format Sections:
| Section | Description |
|---|---|
| Question | The question for the name server |
| Answer | Resource Records answering the question |
| Authority | Resource Records pointing toward an authority |
| Additional | Resource Records holding additional information |
DNS Resolution Process:
- Client queries local DNS server
- If not found, query forwarded to other DNS servers
- Response cached temporarily for future queries
Go deeper:
-
How a DNS Server works — PowerCert's animated tour of name resolution. -
List of DNS record types (Wikipedia) — A, AAAA, NS, MX and many more, with their type IDs. -
RFC 1035 — Domain Names: Implementation and Specification — the core DNS standard, including message format.