AAAA Record — IPv6 Address Mapping

What Is an AAAA Record?

An AAAA record (sometimes called a "quad-A" record) maps a domain name to an IPv6 address. It serves the same purpose as an A record but for the 128-bit IPv6 address space instead of the 32-bit IPv4 space.

BIND Zone File Syntax

; Full IPv6 address
example.com.    3600    IN    AAAA    2001:0db8:85a3:0000:0000:8a2e:0370:7334

; Compressed IPv6 (consecutive zero groups replaced with ::)
example.com.    3600    IN    AAAA    2001:db8:85a3::8a2e:370:7334

; Subdomain
www             3600    IN    AAAA    2001:db8:85a3::8a2e:370:7334

IPv6 addresses use eight groups of four hexadecimal digits separated by colons. Leading zeros within a group can be omitted, and one sequence of consecutive all-zero groups can be replaced with ::.

Dual-Stack Configuration

Most modern deployments use dual-stack networking, where both A and AAAA records exist for the same domain. The client's operating system and network determine which protocol to use:

example.com.    3600    IN    A       203.0.113.50
example.com.    3600    IN    AAAA    2001:db8:85a3::8a2e:370:7334

Modern browsers implement the Happy Eyeballs algorithm (RFC 8305), which races IPv4 and IPv6 connections in parallel and uses whichever succeeds first. This ensures visitors always get the fastest connection regardless of their network capabilities.

Why IPv6 Matters

The IPv4 address space is exhausted. Regional Internet Registries have allocated all available blocks. IPv6 provides approximately 3.4 x 10^38 addresses, solving the scarcity problem permanently. Many mobile carriers and ISPs now assign IPv6 addresses by default.

Adding AAAA records ensures your site is accessible to IPv6-only clients and can improve performance for users on networks that prioritize IPv6 routing.

Validation Rules

An AAAA record value must be a valid 128-bit IPv6 address. Common formatting rules:

• Eight groups of 1-4 hex digits separated by colons
• A single :: can replace one or more consecutive all-zero groups
• Do not mix IPv4-mapped notation (::ffff:192.0.2.1) in AAAA records for standard public DNS

Troubleshooting

If an AAAA record is present but the server does not listen on IPv6, visitors using IPv6 will experience connection timeouts before falling back to IPv4. Always ensure your server is reachable on the IPv6 address before publishing the AAAA record.