Question about AA bit

Barry Margolin barmar at
Tue Nov 29 03:11:55 UTC 2005

In article <dmeq87$13ua$1 at>,
 Hideshi Enokihara <Hideshi.Enokihara at> wrote:

> If DNS Server1 is bind-8, AA bit of this response(4) is set to 1. 
> However, if DNS Server1 is bind-9, AA bit of this response(4) is set to 0. 
> Why is the behavior of bind-8 and bind-9 different like this?

In BIND 8, if the answer wasn't already in the cache, and the server had 
to recurse, it simply passed the response it got through unchanged.  So 
if the authoritative server answered with the AA bit set to 1 (as it 
should), so did the response to the client.  But if the answer came from 
the cache, the response would always have AA=0.

This was considered a bug, because the AA bit is supposed to indicate 
whether the server sending the answer is actually authoritative.  It was 
fixed in BIND 9, so AA=1 only when the answer comes from authoritative 
data, and AA=0 when the answer comes from cache or recursing immediately.

Barry Margolin, barmar at
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***

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