[dns-operations] TLD(s) for private use

[Mark Andrews]

In message <5e4bd2ab-0795-b5c5-2889-cc1354fd64c2 at jrcs.co.uk>, James Stevens writes:
> 
> 
> On 11/09/17 14:52, Suzanne Woolf wrote:
> > 
> > On Sep 9, 2017, at 2:29 PM, "John Levine" <johnl at taugh.com> wrote:
> > 
> >> In article <97ad36f6-4b83-8db9-1bab-e88466988e77 at jrcs.co.uk> you
> >> write:
> >>> I've not yet seen any response as to why a prefix that includes
> >>> one or more UNDERSCORE wouldn't be a viable solution - e.g.
> >>> "zz__" - or even all "[LETTER][LETTER]__" - where "XN__" could be
> >>> IDN?
> >> 
> >> Because you can't use underscores in hostnames.  Even if it's not
> >> on the public Internet, you will run into too much software that 
> >> correctly refuses hostnames that aren't ldh.
> > 
> > Indeed, I'd regard LDH compliance as essential. See also
> > https://www.icann.org/resources/pages/universal-acceptance-2012-02-25-en;
> > the "universal acceptance" problem, as stated, is rather wider than
> > the requirement here, because we were talking about locally scoped
> > names-- but assuming "lowest common denominator" software and
> > operational practice is pretty important if you're trying to draft a
> > solution that works for even most of the people, most of the time.
> 
> It would be impossible to disagree - just interesting to see that
> underscore in public names is astonishingly common - like SRV records,
> so I assumed underscore was reasonably well supported.

They are well supported by nameservers.  You just don't want them
in hostnames.  SRV uses underscores so that the labels it prepends
cannot clash with a legal hostname label.

Microsoft used _gc.example.com in AD because _gc was not a legal
hostname so it should not clash with any name that was already in
use.

Mark

> https://en.wikipedia.org/wiki/SRV_record
> https://tools.ietf.org/html/rfc2782
> 
> And PSL requires you add "_psl" to zones
> 
> https://publicsuffix.org/
> 
> 
> ...etc...
> 
> 
> 
> James
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-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org