Principles for Unicode Code Point Inclusion in Labels in the DNS Root

Document Type Expired Internet-Draft (individual)
Authors Andrew Sullivan  , Dave Thaler  , Olaf Kolkman 
Last updated 2012-12-07 (latest revision 2012-06-05)
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This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at


Traditionally, the management of the DNS root zone permitted only "alphabetic" labels. As long as the root zone included only ASCII characters, and as long as there was only one form of a label, the restriction plainly meant that only the letters A-Z and a-z were permitted. The advent of internationalized labels using IDNA2008 presents some complications for the restriction. One of the complications is the meaning of the term "alphabetic" when applied to the Unicode code points in U-labels. This memo presents a set of principles that can be used to determine whether a Unicode code point may be wisely included in the repertoire of permissible code points in a U-label in a zone.


Andrew Sullivan (
Dave Thaler (
Olaf Kolkman (

(Note: The e-mail addresses provided for the authors of this Internet-Draft may no longer be valid.)