The AA bit is a useless bit of frippery in the DNS protocol.

[Jonathan de Boyne Pollard]

KD> Is this important? I have yet to find an application that
KD> cares about the setting of the AA bit.

I've found three: dnstracer, Sendmail, and BIND.

<URL:http://homepages.tesco.net./~J.deBoynePollard/FGA/dnstracer-incorrect-algorithm.html#RFCNonCompliance>
<URL:http://groups.google.com./groups?selm=bdprmb%242ncu%241%40FreeBSD.csie.NCTU.edu.tw>
<URL:http://groups.google.com./groups?selm=c3o04s%248tn%241%40sf1.isc.org>

Of course, the "AA" bit in DNS responses *is* a useless bit of frippery 
in the DNS protocol.  In using it, all three of those applications are 
broken.

<URL:http://groups.google.com./groups?selm=3E9C4ABF.D8DE6467%40tesco.net>

Indeed, for quite a few years now every few months in the various DNS 
server discussion fora someone new has come along having hit the bug in 
BIND that results from its daft "credibility" mechanism.

<URL:http://cr.yp.to/djbdns/bugtraq/20000112082807-15140-qmail@cr-yp-to>