DNS/DJBについて、ここに記述してください。

Returning NXDOMAIN for empty nonterminals is not a bug.

http://www.ietf.org/mail-archive/web/dnsext/current/msg11084.html

archive: http://marc.info/?t=130132703600002&r=1&w=2 

Bottom line: On behalf of the millions of users who rely on my DNS
software (and other deployed software that signals empty nonterminals
with NXDOMAIN), I object to any attempt to change the definition of
NXDOMAIN from the RFC 2308/Vixie 1999/BIND 9/tinydns/etc. definition
into something that applies to subdomains. In particular, I object to
the dnsext-reimprove document.

Vixie: