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[DNSOP] Re: ordering of RRSets in the answer section of a DNS response

Florian Weimer <fw@deneb.enyo.de> Fri, 16 January 2026 10:35 UTC

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From: Florian Weimer <fw@deneb.enyo.de>
To: Dave Lawrence <tale=40dd.org@dmarc.ietf.org>
In-Reply-To: <26985.4353.270647.420916@gro.dd.org> (Dave Lawrence's message of "Thu, 15 Jan 2026 11:08:33 -0500")
References: <9175DF63-77F9-4B4C-9EA9-76B30F941F84@strandkip.nl> <875x94rufa.fsf@mid.deneb.enyo.de> <26985.4353.270647.420916@gro.dd.org>
Date: Fri, 16 Jan 2026 11:35:16 +0100
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Subject: [DNSOP] Re: ordering of RRSets in the answer section of a DNS response
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* Dave Lawrence:

> Florian Weimer writes:
>> I think it's been previously observed that compression is not actually
>> optional in practice, that is, the first answer record needs to start
>> with 0xc0 0x0c.  It's not really related to ordering, but it fits
>> the underlying theme of producing maximally compatible responses.
>
> Well, it is at least minimally related to ordering in that it insists
> on the qname being first in Answer.
>
> I'd like to hear what software out there is requiring this though.  Is
> it a/some library stub(s)?

If I recall correctly, it was a DNS proxy of some kind.  Not very
well-behaved, obviously, but sufficiently widely deployed so that it
mattered to some recursive resolver operators.

I could not find a reference it, hopefully someone else will remember
and has access to relevant (potentially private) email archives.

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