What are A and AAAA records?

Every device on the internet has an IP address. The older kind, IPv4, looks like 192.0.2.10, and an A record in DNS ties it to your domain name. The newer kind, IPv6, is longer, like 2001:db8::10, and the record that ties it to your domain is called AAAA. A site can have both; the browser picks whichever answers faster.

Why it matters

IPv4 addresses have run out, and many providers, mobile networks in particular, give their users IPv6, sometimes only IPv6. Those users usually reach an IPv4-only site through a translator in the provider’s network (NAT64), an extra hop that can be slower or break. With an AAAA record they connect to your site directly. Missing IPv6 is not an error, which is why CheckNet shows it only as a warning.

Add an AAAA record

1. Ask your host, or look in its panel, whether your server has an IPv6 address. If the site sits behind a CDN or proxy, that service usually provides IPv6 itself and only needs it switched on in its settings.
2. Make sure the web server listens on IPv6 too, and the server’s firewall allows ports 80 and 443 over IPv6.
3. In your domain’s DNS panel, create a record of type AAAA, name @, with the server’s IPv6 address; if you use www, do the same for it.
4. Keep the existing A record so people with only IPv4 can still reach the site.
5. Wait a few minutes and check the domain again on CheckNet’s DNS page.

example.com.      A     192.0.2.10
example.com.      AAAA  2001:db8::10
www.example.com.  AAAA  2001:db8::10

Common problems

• An AAAA record, but the site does not answer over IPv6: this is worse than no IPv6, because some programs try IPv6 first and hang until it fails. Either fix the web server and firewall, or remove the AAAA record.
• The wrong address: addresses starting fe80:: or fd00:: are local and cannot be reached from the internet. Get the server’s public address from your host.
• SSL certificates: a certificate is issued for the domain name, not the IP, so IPv6 needs no separate certificate; just make sure the same web server answers on both addresses.

Your own connection cannot tell you whether the site works over IPv6, because you may not have IPv6 yourself. From a machine that has IPv6, run curl -6 -I https://example.com; if response headers come back, the site works over IPv6.

Check it with CheckNet

On CheckNet’s DNS page, look at the rows “has an IPv4 address” and “has an IPv6 address”. If the IPv6 row is a warning, no AAAA record was found. The addresses themselves are in the records table, next to type A and AAAA.