Re: [dbound] [art] [DNSOP] not DNAME, was Related Domains By DNS (RDBD) Draft

John C Klensin <> Thu, 28 February 2019 03:52 UTC

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Date: Wed, 27 Feb 2019 22:52:13 -0500
From: John C Klensin <>
To: John R Levine <>
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Subject: Re: [dbound] [art] [DNSOP] not DNAME, was Related Domains By DNS (RDBD) Draft
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--On Wednesday, February 27, 2019 20:48 -0500 John R Levine
<> wrote:

> On Wed, 27 Feb 2019, John C Klensin wrote:
>> at least one aspect of it is probably worth mentioning.  It
>> requires understanding "tree" but not any special
>> understanding of IDNs, variants, etc.
> You don't even have to go that for.

Actually, you are identifying cases I was deliberately avoiding,
precisely because fixes have been proposed that might almost
work but that still don't solve, or allow solutions for, the
tree problem.

>  Let's say you do this:
> Then will be an alias for, but DNAMEs
> only affect names below themselves, so will remain
> undefined, and you can't put a CNAME and a DNAME on the same
> name.  This makes it useless for what most people imagine they
> want to use it for.


> There's the additional issue that an MX with a target of a
> CNAME or DNAME doesn't work reliably,

"doesn't work reliably" may or may not be a synonym for "is
explicitly prohibited by SMTP" but the latter is true is any

>  and the point you made
> that if you've got variants, you can get a very bushy tree
> every time a variant character appears in a label.

Yep.  And that raises several other issues with this proposal,
all of which I was trying to avoid because they are (i) more
complicated and (ii) involve more or less subtle DNS issues.

> This issue has been argued at great length with proposals like
> BNAME and CLONE so let's not redo it here.