What Is an AAAA Record? Examples and A vs. AAAA Differences

A domain doesn't have one IP address -- it has up to two entirely separate kinds, stored as two different DNS record types. An A record holds an IPv4 address (like 192.0.2.10). An AAAA record (said "quad-A") holds an IPv6 address (like 2606:4700::6810:84e5). For illustration, an AAAA record example in a zone file reads example.com. 3600 IN AAAA 2606:4700::6810:84e5, and the matching A record reads example.com. 3600 IN A 192.0.2.10. They're queried independently, answered independently, and a domain can have one, the other, both, or -- less commonly today -- neither reachable from a given network.

Why two address families exist at all

IPv4 addresses are 32-bit numbers, which caps the total possible addresses at around 4.3 billion -- a number the internet has already exhausted. IPv6 uses 128-bit addresses, an address space so large that practical exhaustion isn't a realistic concern. IPv6 was designed as the long-term replacement, but because the two protocols aren't compatible at the wire level, the internet has spent two decades running both side by side rather than cutting over all at once.

What an AAAA record means for a lookup

• A domain with only an A record is IPv4-only -- still extremely common, especially for smaller or older infrastructure.
• A domain with both records is dual-stacked -- most large platforms and CDNs work this way today.
• A client (browser, app, or server) that supports both will generally prefer IPv6 when both are available and the network path actually supports it.
• Seeing an AAAA record doesn't guarantee you can reach it -- your own network or ISP still needs working IPv6 connectivity.

How a dual-stack client actually picks one

When both records exist, most modern operating systems don't just blindly try IPv6 first and give up if it fails. They use an algorithm known as Happy Eyeballs (RFC 8305): the client fires off connection attempts to the IPv6 address and a fallback IPv4 address nearly simultaneously, with the IPv6 attempt given a small head start, and simply uses whichever connection completes first. This is why a domain with a broken or unreachable AAAA record usually still loads without any visible delay for most users -- the IPv4 fallback wins the race silently -- even though a naive "try IPv6, then give up and retry IPv4 from scratch" approach would have introduced a multi-second stall.

If you're debugging connectivity, checking both is worth doing before anything else: a missing AAAA record ruling out IPv6 as the culprit (or confirming it as one) takes a single lookup and immediately narrows the problem space.

A dual-stack answer isn't always symmetric

It's easy to assume a domain's A and AAAA records point at equivalent, interchangeable infrastructure, but that's not guaranteed. A CDN might have rolled out IPv6 support to some edge locations before others, meaning the AAAA record routes through a smaller subset of the same network than the A record does. An origin server migrated to new IPv4 hosting might still be serving IPv6 traffic from an older, soon-to-be-decommissioned host if the AAAA record wasn't updated in the same change. Treating the two record types as independently maintained -- because they genuinely are -- rather than assuming a single "the server" behind both, avoids a class of migration mistake where one address family gets updated and the other quietly gets left behind.