Re: [DNSOP] Variant bad idea of the day

"John R Levine" <johnl@taugh.com> Wed, 02 January 2019 19:48 UTC

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Date: 2 Jan 2019 14:48:49 -0500
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From: "John R Levine" <johnl@taugh.com>
To: "Brian Dickson" <brian.peter.dickson@gmail.com>
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Subject: Re: [DNSOP] Variant bad idea of the day
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On Wed, 2 Jan 2019, Brian Dickson wrote:
>> Let's assume for the purposes of argument that we have a DNS server that
>> knows how to translate between A-labels an U-labels.  Then I invent this
>> DNS record
>
> Is it the case that you have a bunch of labels that you want to have
> treated as equivalent, and that at the terminus of any given FQDN involving
> a sequence of equivalence-sets of labels, there is a single "canonical"
> owner name for all the RRtypes/RRsets?

Basically yes, it's the IDN version of ASCII upper/lower case equivalence. 
If you have a label ABCD in your zone, it'll match abcd and Abcd and 14 
other upper-lower combinations.

> This is to use DNAMEs for all of the variants, with all names being
> letter-digit-hyphen format (a-label?), so for i18n stuff, xn--* format.

Unfortunately this is a WKBI for multiple reasons:

* DNAME only maps names below it, not the name itself.  This is why this 
approach completely failed in the .CAT TLD to try and map accented to
unaccented names.

* DNAME only maps one name at a time, but a name can have many variants 
and there can be variants at every level, e.g., if a name is FOO.BAR, 
there's 8 possible variants for each label.

* DNAME synthesized names are not equivalent to the original, particularly 
for mail since MX to CNAME is not allowed and the rule is spottily 
followed.

Taiwan has a DNAME to map the simplified .台湾 to .台灣.  It sort of
works.

$ dig xn--kprw13d. dname

;; ANSWER SECTION:
xn--kprw13d.            3600    IN      DNAME   xn--kpry57d.

> This is to use authority-size zone file references, and pull in identical
> zone files by reference, rather than keep the parallel zones as separately
> maintained entities.

That's not exactly a WKBI, but it only solves a small part of the problem. 
You can use it to map equivalent zones line foo.ngo and foo.ong, but it 
doesn't handle variant names within the zone.  I use it in my DNS toaster 
for a user who has a lot of vanity zones and want them all to point to the 
same place.

Regards,
John Levine, johnl@taugh.com, Taughannock Networks, Trumansburg NY
Please consider the environment before reading this e-mail. https://jl.ly