[dns-operations] NXDOMAIN vs NOERROR/no answers for non-existant records

[Shumon Huque]

On Fri, Apr 3, 2020 at 7:35 AM Matthew Richardson <matthew-l at itconsult.co.uk>
wrote:

> I am observing responses from particular authoratitive servers for
> non-existant domains, which is puzzling me.  I thought I understood this
> topic, but am now having doubts...
>
> Consider two (real) non-existant records (which are not empty non-terminals
> - there is nothing below them):-
>
>         doesnotexist.mtgmon.itconsult.net
>         doesnotexist.monitor.itconsult.net
>
> where mtgmon.itconsult.net & monitor.itconsult.net are delegated to
> different authoratitives.
>
> Querying each against the authoratitives returns NOERROR with "ANSWER: 0"
> for the first one and NXDOMAIN for the second, behaviour which is
> consistent across all the authoratitives:-
>

The second one,  doesnotexist.monitor.itconsult.net., does not appear to be
delegated from its parent. That's why you're getting NXDOMAIN - that
response is coming from the parent zone: itconsult.net.

>> Query: doesnotexist.monitor.itconsult.net. A IN at zone itconsult.net.
>>   Send to zone itconsult.net. at address 193.201.42.1
ERROR: NXDOMAIN: doesnotexist.monitor.itconsult.net. not found

Shumon.
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