authoritative: use other than for zone xfer?

Barry Margolin barmar at genuity.net
Tue Jun 27 15:08:13 UTC 2000


In article <200006270249.MAA05917 at bsdi.dv.isc.org>,
 <Mark.Andrews at nominum.com> wrote:
>
>> Len Conrad wrote:
>> 
>> > Other than enabling/disabling zone transfers, what other
>> > advantage/disadvantage is there to an NS being authoritative or not?
>> >
>> > eg, who/what else cares if an authoritative NS is answering with correct
>> > data but non-authoritatively?
>
>	Namservers.  If aa is not set they will reject answers as being
>	possibly in error.

Do they really reject non-authoritative answers?  I thought they just
logged "Lame server" but used the answer anyway.

I think what BIND may do is reduce the credibility of the answer and
accelerate TTL expiration (like it does for records that come from the
Additional Records section of a response).

I think sendmail makes use of the AA flag, though.  Before querying
specifically for MX and A records, it sends an ANY query so it can try to
get them both in one shot.  If the answer is authoritative and contains
A records but no MX records, it knows that it's complete and it doesn't
need to ask specifically for MX records.  A non-authoritative answer that
contained just A records could be due to the fact that the local server
simply doesn't have the MX records in its cache yet.

-- 
Barry Margolin, barmar at genuity.net
Genuity, Burlington, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.



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