authoritative: use other than for zone xfer?

[Mark.Andrews at nominum.com]

> 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.
> 
> Off the top of my head, if a nameserver answers with RCODE=NOERROR and
> ANCOUNT=0, then I believe the querier needs to look at the AA bit to
> distinguish between a referral and "no data of requested type found" from
> an authoritative nameserver. If it's an authoritative answer, the query is
> finished, but if the querier thinks it's an attempted referral, it'll mark
> the server as lame and keep on looking elsewhere for the data.  So there's
> at least one case where the AA bit is necessary even for the basic
> query-resolution function of DNS.

	No. AA has no effect on whether the answer contain a referral or
	not.  See RFC 2308 for a fuller description of how to differentiate
	the different answers.

	Mark
--
Mark Andrews, Nominum Inc.
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