AAAA Record Lookup

An IPv6 address looks long and strange, but getting it into DNS is as simple as for IPv4: add an AAAA record. The record is called quad-A because an IPv6 address is four times as long as an IPv4 one. The page asks a resolver for a name’s AAAA records and shows them in both of the forms you meet in practice.

What the record does

An AAAA record maps a host name to a 128-bit IPv6 address. A site that publishes both A and AAAA records is reachable by either protocol, and clients choose. Browsers and operating systems prefer IPv6 when it works, using a method called Happy Eyeballs (RFC 8305) that starts the IPv4 attempt shortly after the IPv6 one, so a broken IPv6 path costs only a fraction of a second. A name without any AAAA record keeps working for everyone with IPv4; users on IPv6-only networks reach it through a translator (NAT64), which adds a hop.

The two address forms

IPv6 text can be shortened by dropping leading zeros and replacing one run of zero groups with a double colon. RFC 5952 fixes a single canonical way of doing this. The table shows that form, which is what tools print, and the full form with all eight groups of four digits, which is what you need to compare two addresses reliably or to build the reverse name by hand. The IPv6 Expander and IPv6 Compressor convert any address both ways.

The kind column

The last column classifies the address. Most records point at global unicast addresses, which begin with 2 or 3. A unique local address (starting fc or fd) or a link-local one (fe80) in a public name is a sign of a mistake, since neither is routed on the Internet. The documentation prefix 2001:db8::/32 should never appear in a live name either.

Introducing IPv6 safely

Adding an AAAA record is the last step of enabling IPv6, not the first. First the server needs a global address and a firewall that allows the same traffic as for IPv4, then the web server and any load balancer must listen on it, and monitoring should test it separately. Only then publish the record. A frequent cause of slow sites is an AAAA record that was added before the firewall rules were. The IPv6 Test tells you whether your own connection can reach IPv6-only servers, which you need to check it from the outside.

A worked example

Press Sample to look up cloudflare.com. The page lists AAAA records in a table with the address, the full form and the kind. When this guide was reviewed they were global unicast addresses beginning 2606:4700::; in shortened form 2606:4700::6810:84e5 and in full form 2606:4700:0000:0000:0000:0000:6810:84e5. The explanation underneath notes that a name without AAAA records is not broken but needs NAT64 for IPv6-only users. The addresses of large providers change over time; the layout does not.

Limits

A record in DNS shows what is published, not whether the host answers on that address. Some resolvers also synthesise AAAA records (DNS64) for IPv6-only clients; that is a service of the resolver, not data published by the domain. For a complete view of a domain use the DNS Lookup.

Related tools

• A Record Lookup shows the IPv4 side of the same name.
• IPv6 Expander writes any address in full.
• IPv6 Test checks your own connection’s IPv6 reachability.
• DNS Lookup shows every common record type.