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DNS Resource Records Summary

Jun 16, 2025

Overview

This lecture explains common DNS resource records found in a DNS server configuration file, their purposes, and how they facilitate name resolution and other DNS-related functions.

DNS Resource Records Overview

  • DNS servers use resource records to store information about domain names, IP addresses, and related data.
  • Records can map names to IPs, provide certificate info, define aliases, and support various DNS services.

Start of Authority (SOA) Record

  • SOA record appears at the top of a DNS configuration and contains DNS zone details.
  • Includes serial number, domain name, retry/expiration times, and storage durations for zone information.

Address Records (A and AAAA)

  • A record maps a domain name to an IPv4 address (e.g., www.example.com to 162.59.246.1).
  • AAAA (Quad A) record maps a domain name to an IPv6 address.

Canonical Name (CNAME) Record

  • CNAME creates an alias for a domain, allowing multiple names to point to a single server.
  • Example: chat.example.com and ftp.example.com can both map to mail.example.com.

Mail Exchanger (MX) Record

  • MX record specifies the mail server responsible for receiving email for the domain.
  • Additional name resolution is needed if only the mail server's name (not IP) is given.

Text (TXT) Record

  • TXT records store human-readable text for various purposes, like SPF and DKIM email security settings.
  • SPF (Sender Policy Framework) indicates authorized mail servers for sending emails on behalf of the domain.
  • DKIM (DomainKeys Identified Mail) stores public keys for verifying digital signatures on email.

Name Server (NS) Record

  • NS records specify which servers are authoritative for a given domain.
  • Each NS record lists a name server that handles DNS requests for the domain.

Pointer (PTR) Record

  • PTR records map IP addresses (in reverse) to domain names, supporting reverse DNS lookups.
  • Used to find the domain name associated with a specific IP address.

Key Terms & Definitions

  • Resource Record — An entry in a DNS database containing information about a domain.
  • SOA Record — Start of Authority; contains primary info about the DNS zone.
  • A Record — Maps a name to an IPv4 address.
  • AAAA (Quad A) Record — Maps a name to an IPv6 address.
  • CNAME Record — Creates an alias from one name to another canonical name.
  • MX Record — Designates mail servers for a domain.
  • TXT Record — Stores text data, often for SPF and DKIM.
  • NS Record — Specifies authoritative DNS servers.
  • PTR Record — Maps IP addresses to domain names (reverse lookup).

Action Items / Next Steps

  • Review a DNS configuration file and identify each discussed record type.
  • Prepare to match example DNS queries with their corresponding record responses.

Full transcript