AAAA Records in DNS: The IPv6 Half of Your Domain, Explained

An AAAA record maps a domain name to an IPv6 address, and that is the entire idea - it is the exact counterpart of the A record, which maps to IPv4. The name is ‘quad-A’ because an IPv6 address is four times the size of an IPv4 one (128 bits versus 32), so the record type got four A’s instead of one. If your domain has an AAAA record, IPv6-capable clients can reach it over IPv6; if it does not, they fall back to IPv4 through your A record.

It sounds like trivia until a mismatched or half-configured AAAA record makes a site load slowly for some users and nobody can work out why. Here is the practical version.

Table of contents

• A and AAAA, side by side
• When you actually need one
• The failure mode: a broken AAAA is worse than none
• Checking your AAAA records
• How this fits the rest of the stack
• FAQ

A and AAAA, side by side

; A record - IPv4
example.com.    3600    IN    A       203.0.113.10

; AAAA record - IPv6
example.com.    3600    IN    AAAA    2606:4700:4700::1111

Same job, different address family. A resolver asks for both. A client with working IPv6 will generally prefer the AAAA result; a client without IPv6 uses the A. Most domains have an A record; not all have an AAAA, because not every host has an IPv6 address to point at.

When you actually need one

• Your host has an IPv6 address. If your server or CDN offers IPv6, add the AAAA so IPv6 clients connect natively instead of routing through IPv4 translation.
• You care about mobile and international reach. Large mobile networks are heavily IPv6, and some regions are IPv6-first. An AAAA record can mean a faster, more direct path for those users.
• Your CDN or platform sets it for you. Many managed platforms publish both A and AAAA automatically. In that case you do nothing - it is already there.

If your server has no IPv6 address, you do not add an AAAA record pointing at a made-up one. A missing AAAA is fine; a wrong AAAA is the thing that breaks.

The failure mode: a broken AAAA is worse than none

This is the part worth internalizing. If you publish an AAAA record pointing at an IPv6 address that does not actually serve your site, IPv6 clients try it first, wait for it to time out, and only then fall back to IPv4. The result is a site that is slow to load for exactly the users on IPv6 - and fine for everyone else, so it is maddening to reproduce.

The rule: only publish an AAAA record if that IPv6 address genuinely answers on the ports you serve. An AAAA you set up ‘to be modern’ and never tested is a latency bug waiting for an IPv6 user to find it.

Checking your AAAA records

dig example.com AAAA +short     # returns the IPv6 address, or nothing
dig example.com A +short        # the IPv4 counterpart

# Test that the IPv6 address actually serves the site
curl -6 -I https://example.com  # forces IPv6; should return headers

dig AAAA tells you what is published; curl -6 tells you whether that address actually works. Run both. A published AAAA that curl -6 cannot reach is precisely the slow-for-some-users bug described above, and this two-command check is how you catch it before your users do.

How this fits the rest of the stack

An AAAA record is a small thing that is either correct or quietly harmful - much like most DNS and infrastructure settings, where the danger is the misconfiguration that only some users hit. When a managed platform serves your site, it typically publishes and tests both A and AAAA for you, removing the footgun entirely. The RunxBuild hosting calculator shows a site and its bandwidth as line items, and the RunxBuild dashboard is where you attach a domain and get the records set correctly without hand-editing an IPv6 address.

Useful related references:

• What does flushing DNS actually do
• DNS address could not be found
• How to change your DNS settings
• Static sites and domains on RunxBuild

FAQ

What is an AAAA record in DNS?

An AAAA record maps a domain name to an IPv6 address, exactly as an A record maps to an IPv4 address. It is called quad-A because IPv6 addresses are 128 bits, four times the size of a 32-bit IPv4 address. IPv6-capable clients use the AAAA record to connect natively; clients without IPv6 fall back to the A record.

What is the difference between an A record and an AAAA record?

Only the address family. An A record points to an IPv4 address like 203.0.113.10; an AAAA record points to an IPv6 address like 2606:4700:4700::1111. They serve the same purpose - telling clients where to reach a domain - and a domain commonly has both so clients can use whichever protocol they support.

Do I need an AAAA record?

Only if your server or CDN has an IPv6 address that actually serves your site. If it does, adding an AAAA gives IPv6 clients a direct path, which helps on mobile and in IPv6-first regions. If your host has no working IPv6, a missing AAAA is perfectly fine - do not invent one, because a broken AAAA is worse than none.

Why does a wrong AAAA record slow down my site?

Because IPv6 clients try the AAAA address first. If it points to an IPv6 address that does not serve your site, those clients wait for a timeout before falling back to your IPv4 A record, so the page loads slowly for IPv6 users only. Publish an AAAA record just for an address you have confirmed answers on the ports you serve.

How do I check my domain’s AAAA record?

Run dig example.com AAAA +short to see the published IPv6 address, and dig example.com A +short for the IPv4 counterpart. Then confirm the IPv6 address actually works with curl -6 -I https://example.com, which forces an IPv6 connection. A published AAAA that curl -6 cannot reach is the cause of slow loads for IPv6 users.