On Thu, Oct 01, 2026 at 12:43:11PM +0200, Petr Špaček wrote: > b) should it trigger FORMERR (= whole message ignored)
I missed this part: perhaps this is a BIND-specific question, i.e.,
"trigger FORMERR". BIND's resolver's response parser (assuming it's
still resquery_response()) used DNS_R_FORMERR result for malformed
responses. But BIND did fallback for that result and didn't return
FORMERR in this case to a client. What I meant to say is that the
"trigger FORMERR" part is an implementation detail. I haven't looked at
recent BIND code which may have changed and so my answer may be
incorrect.
Such a response should be considered malformed (what BIND used
DNS_R_FORMERR internally for), and usually it's SERVFAIL that's returned
to a resolver's client if that leads to processing failure. FORMERR is
not returned in this case to the client; FORMERR is usually returned
when the nameserver is unable to parse the client's request message
(query). You can find this stated in RFC 1035 section 4.1.1:
> 1 Format error - The name server was
> unable to interpret the query.
Mukund
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