Re: [DNSOP] Fundamental ANAME problems

Tony Finch <dot@dotat.at> Tue, 06 November 2018 19:03 UTC

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Date: Tue, 6 Nov 2018 19:03:41 +0000
From: Tony Finch <dot@dotat.at>
To: Ray Bellis <ray@bellis.me.uk>
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Subject: Re: [DNSOP] Fundamental ANAME problems
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Ray Bellis <ray@bellis.me.uk>; wrote:
> On 06/11/2018 20:44, Tony Finch wrote:
>
> > If you are using an _prefix without any meaning of its own but only to
> > move a record away from the apex (so that it can be delegated or CNAMEd)
> > and also using a specific RR type or an RDATA prefix, then wildcards do
> > not conflict.
>
> I believe they still do, e.g.
>
> _domainkey.*.example.com IN TXT ...

You obviously can't do that, but you can do:

	*.example.com TXT ...

and it'll match queries for tag._domainkey.whatever.example.com.

Except that it won't work very well for the specific example of _domainkey
records, because of the tag selector in the qname.

It will probably work OK for DMARC records which do not have any selectors
in the qname and which have a nice prefix in the TXT RDATA.

For the runing LJ example, if you want to match

	_http.fanf.livejournal.com HTTP ...

the zone admin can publish

	*.livejournal.com HTTP ...

But for the HTTP case, the record itself provides enough indirection so
there isn't any need for a _prefix to allow delegation as you might want
to for DMARC.

Tony.
-- 
f.anthony.n.finch  <dot@dotat.at>;  http://dotat.at/
Fair Isle, Faeroes, Southeast Southeast Iceland: Southeasterly 5 to 7,
occasionally gale 8 in Fair Isle. Rough, occasionally very rough. Occasional
rain. Moderate or good, occasionally poor.