Do you have Linux/FreeBSD hosts on IPv4-only networks? Have you checked your DNS query logs recently? If you have, you’ll might be wondering what all the queries for AAAA records are.

The above table is from a document titled DNS stub resolver behavior of IPv6 ready hosts. It was written in 2006, and the situation remains, at least as far as Linux is concerned.

RHEL/Centos 5.6 and SLES 11 SP1 insist on having its stub resolver query for AAAA records even if IPv6 connectivity is completely disabled in the kernel.

Henk Jan mentioned that this bug has been resolved (pun not intended) in Ubuntu with a patch to glibc.

I urge vendors to add a switch to the resolver configuration allowing us to enable or disable this behavior at our discretion.