An AAAA record (pronounced "quad-A") maps a hostname to a 128-bit IPv6 address. It is the IPv6 counterpart of the A record; the name reflects that an IPv6 address is four times as long as an IPv4 one.
Why it matters
Clients that have working IPv6 prefer it, so a hostname with both A and AAAA records is reached over IPv6 first on those networks. If the AAAA record points at a server that is not actually listening on IPv6, those visitors see timeouts or slow fallbacks while IPv4 users see nothing wrong. This is a classic cause of "works for me, not for them" reports. Many mobile carriers are IPv6-heavy, so it matters.
Example
example.com. 300 IN AAAA 2001:db8:10::aVerify with dig +short example.com AAAA and test the server directly with curl -6 -I https://example.com/. The 2001:db8::/32 range is reserved for documentation.
Common mistakes
- Publishing an AAAA record while the web server, firewall or load balancer only handles IPv4.
- Moving hosts and updating only the A record, leaving the old AAAA behind.
- Testing only from an IPv4-only connection, so the broken IPv6 path is never noticed.
- Writing addresses incorrectly:
::can replace only one run of zero groups per address.
Related
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