[dns-operations] NXDOMAIN and negative caching

Andrew Boling aboling at gmail.com
Tue Feb 2 00:36:26 UTC 2016

On Mon, Feb 1, 2016 at 6:21 PM, Michael Smitasin <mnsmitasin at lbl.gov> wrote:
> What I infer from that (perhaps it's explicitly stated elsewhere?) is two
> things:
> - An NXDOMAIN indicates /no/ records exist for that name.
> - When an NXDOMAIN is cached, it will be returned for /any/ QTYPE matching
> the same QNAME, QCLASS.
Both inferences are correct. In particular, you'll want to pay attention to
RFC 2038 §2.2 which describes the synthetic "NODATA" state. This is what
you would expect to find if the A record exists but the NS record does not.
RFC 2038 §5 goes on to explain the difference in handling between NXDOMAIN
and NODATA. Note that the negative caching changes from a <QNAME, QCLASS>
association to <QNAME, QTYPE, QCLASS> in the case of NODATA.

§2.1, §2.2, and §5 should be sufficient to demonstrate that your server is
behaving correctly and that the authoritative server is incorrectly
handling the NODATA case.
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