Recently IPv6 addresses were added to some of the DNS root servers. Many have tauted this as one of the last barriers to running pure IPv6 networks. However, in reality this is not the case. There are still two major problems to overcome.

First, many of the Top Level Domains (TLDs) do not support IPv6 (AAAA) glue records. This is the next "layer" in the hierarchy below the roots mentioned above. It includes major TLDs such as .org, .us, and most other countries. Without support at these TLDs, DNS servers (such as those for nabber.org) cannot be contacted natively with IPv6, an IPv4 lookup must be used instead.

Second, the domain registrars also need to support IPv6 (AAAA) glue records. These registrars typically have a web interface in which to change the IPv4 glue records and name of the domain's DNS servers to use. Many of the registrars have not added this support for IPv6 glue records so that it is accessible to end users. The end result is the same, IPv4 must be used to query DNS records at second level domains like nabber.org, IPv6 cannot be used.

As it stands today, the only way DNS can be used with ONLY IPv6 is if 1) the requested TLD supports it, and 2) the domain registrar for that domain supports it. The odds of having both of these happen is extremely low.

UPDATE: My DNS Check tool will now check for full IPv6 compliance as described above.