"SRV-Style" labels and "IDN"

Mark Andrews Mark_Andrews at isc.org
Wed Apr 1 00:15:36 CEST 2009

In message <8BC845943058D844ABFC73D2220D4665081E4704 at nics-mail.sbg.nic.at>, "Al
exander Mayrhofer" writes:
> Hi,
> I'm currently reading through the idnabis-Documents, and didn't find a
> clear answer to the following issue:
> of draft-ietf-idnabis-defs-08 defines an IDN as "name that may
> contain any mixture of NR-LDH-labels, A-labels, or U-labels".  From what
> i read, that means that an IDN may not contain a "SRV-style" label,
> starting with an underscore. A few lines later, it is clarified that
> such a label is not an "Internationalized Label". There's no text about
> those labels in the definition of "IDN". Therefore, from the definition,
> the following example:
>    _sip._tcp.<A-Label>.<tld>
> Would not be an IDN. My questions now, unless i have missed something:
> - Is my assumption correct that the example is not an IDN?
> - If it is not an IDN, what is it? 

	This reflects the mis-use of DOMAIN in IDN.  In reality
	IDN's should be named IHN's (International HOST Names).
	LDH is a HOST NAME restriction, not a DOMAIN NAME restriction.

	In general you won't ever enter _sip._tcp.<A-Label>.<tld>
	in a application.  You will enter <A-Label>.<tld> and
	_sip._tcp will be prepended as part of the discovert process.

	_sip._tcp.<A-Label>.<tld> is not a host name the same way
	that _sip._tcp.example.net is not a host name but both are
	legal domain names.


> Thanks,
> Alex Mayrhofer
> nic.at
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Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at isc.org

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