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DNS Records

This guide explains all common DNS record types, their purposes, usage scenarios, and examples, including IPv4 and IPv6 considerations.

A Record (Address Record)

  • Purpose: Maps a domain or subdomain to an IPv4 address.
  • Use case: Your server has an IPv4 address and you want your domain to resolve to it.
  • Format: 123.45.67.89
  • Example:
Host Type Value
@ A 123.45.67.89
www A 123.45.67.89
  • Notes: Most websites still rely on A records since IPv4 is universally supported.

AAAA Record (IPv6 Address Record)

  • Purpose: Maps a domain or subdomain to an IPv6 address.
  • Use case: Your server supports IPv6 and you want your site accessible on IPv6 networks.
  • Format: 2001:0db8:85a3::8a2e:0370:7334
  • Example:
Host Type Value
@ AAAA 2001:db8::1234
  • Notes: Modern browsers prefer IPv6 if available. If both A and AAAA exist, IPv6 is tried first. Then fallbacks to IPv4.

CNAME Record (Canonical Name)

  • Purpose: Points a subdomain to another hostname, not an IP.
  • Use case: You want blog.yourdomain.com to resolve to yourdomain.com or username.github.io.
  • Format: hostname
  • Example:
Host Type Value
www CNAME yourdomain.com
blog CNAME yourdomain.com
notes CNAME username.github.io
  • Notes: Cannot be used for the root domain (@). Useful for subdomains that should follow another hostname’s IP automatically.
  • Alternatively you can use IP addresses as a value instead of hostnames. But it is preferable to use hostnames because if the IP address changes, you only need to update it in one place.

MX Record (Mail Exchange)

  • Purpose: Directs email to your mail server.
  • Use case: You want your domain to receive emails.
  • Format: priority + mail server hostname
  • Example:
Host Type Value
@ MX 10 mail.yourdomain.com
  • Notes: Lower priority numbers have higher priority. Multiple MX records provide redundancy.

TXT Record (Text Record)

  • Purpose: Store arbitrary text for verification, SPF, DKIM, or DMARC.
  • Use case: Email authentication, domain verification.
  • Example:
Host Type Value
@ TXT "v=spf1 include:_spf.google.com ~all"
@ TXT "google-site-verification=abc123"
_github-pages-challenge-john.blog TXT 11233122
  • Notes: Important for preventing email spoofing and verifying domain ownership.

NS Record (Name Server Record)

  • Purpose: Specifies which nameservers are authoritative for the domain.
  • Use case: Point your domain to a hosting provider’s DNS service.
  • Format: hostname
  • Example:
Host Type Value
@ NS ns1.hosting.com
@ NS ns2.hosting.com
  • Notes: Typically set at the registrar. Changing NS changes who controls DNS records for your domain.

Relationship Between IPv4, IPv6, and DNS

  • A record → IPv4
  • AAAA record → IPv6
  • If a domain has both A and AAAA, modern clients try IPv6 first and fall back to IPv4 if IPv6 fails.
  • If A and AAAA point to different servers, users may see different content depending on their network.
  • IPv6 adoption depends on OS, network, and ISP support. Older devices/networks may only support IPv4.

Example Combined DNS Setup

Host Type Value Notes
@ A 123.45.67.89 Main website IPv4
@ AAAA 2001:db8::1234 Main website IPv6
www CNAME @ Follows root domain
internal CNAME yourdomain.com Internal subdomain pointing to main server
notes CNAME username.github.io GitHub Pages subdomain
@ MX 10 mail.yourdomain.com Email server
@ TXT "v=spf1 include:_spf.google.com ~all" Email SPF
@ NS ns1.hosting.com Primary nameserver
@ NS ns2.hosting.com Secondary nameserver

This setup ensures:

  • Your website works on IPv4 and IPv6.
  • Subdomains correctly point to GitHub Pages or internal servers.
  • Email is authenticated and reliable.
  • DNS is managed via your chosen authoritative nameservers.