Why AAAA records exist
IPv4 space is exhausted in any practical sense. IPv6 uses 128-bit addresses, written as eight hex groups. The DNS record that holds them is AAAA — four A’s, a bit of engineer humor from the 1990s. Modern operating systems implement Happy Eyeballs: they race IPv6 and IPv4 and use whichever connects first. If your AAAA record points at a dead stack, some users get a slow fallback instead of a clean IPv4 hit.
What to verify
- The address is the one your load balancer or host actually listens on.
- Firewall and web server vhosts accept IPv6, not just DNS.
- Mail servers you list in MX have working AAAA records if you advertise IPv6.
No AAAA is valid if you are IPv4-only. Publishing a broken AAAA is worse than publishing none. Background: IPv4 vs IPv6 DNS.