Caching ANSWER:0

[Fred Morris]

When people think of "negative response caching" I suspect they're
thinking of NXDOMAIN, but there is another negative response: ANSWER:0.
To some extent this is indistiguishable from a referral, and I'm not
sure that caching of (upward) referrals is a sensible concept on its own.

Testing with BIND 9.12 and 9.18 suggests that ANSWER:0 is not cached at
all, and that each recursive request received results in a query from
the caching resolver to the authoritatives (the authoritative is not
running BIND).

I'd appreciate a pointer to an RFC which specifically discusses this.

I'd also appreciate (from someone who's read the code) a statement of
what the intended semantics are, before I go read the code myself.
Presuming that the ANSWER:0 response is authoritative, is there any
expectation regarding content in the ADDITIONAL or AUTHORITATIVE
sections which affects this behavior? NS? SOA?

Thanks in advance...

--

Fred Morris