Glossary

A Record

Definition: A DNS record type that maps a domain name to an IPv4 address, directing browsers to the correct server.

An A record (Address record) is the most fundamental DNS record type. It maps a domain name or subdomain to an IPv4 address, telling DNS resolvers which server to connect to when someone visits your domain.

A Record Format

example.com.     3600    IN    A    104.21.33.85
www.example.com. 3600    IN    A    104.21.33.85

Field breakdown: Name (domain) | TTL (cache duration in seconds) | Class (IN = Internet) | Type (A) | Value (IPv4 address).

A Record vs AAAA Record

  • A record → IPv4 address (e.g. 104.21.33.85)
  • AAAA record → IPv6 address (e.g. 2606:4700:3033::6815:2155)

Modern servers should have both. Browsers prefer IPv6 when available.

Multiple A Records

A domain can have multiple A records pointing to different IPs. DNS resolvers cycle through them (round-robin DNS), distributing load across multiple servers. This is a simple form of load balancing.

Common A Record Configurations

  • @ or blank — points the root domain (example.com) to the server
  • www — points www.example.com to the server
  • mail — points mail.example.com to the mail server
  • * — wildcard, catches all undefined subdomains

Common Mistakes

  • Forgetting to add a www A record separately.
  • Pointing an A record to a hostname instead of an IP (use CNAME for that).
  • Not lowering TTL before planned server migrations.

Verify A records for any domain with the DNS Lookup tool.

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