Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework
RFC 5890

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Internet Engineering Task Force (IETF)                        J. Klensin
Request for Comments: 5890                                   August 2010
Obsoletes: 3490
Category: Standards Track
ISSN: 2070-1721

        Internationalized Domain Names for Applications (IDNA):
                   Definitions and Document Framework

Abstract

   This document is one of a collection that, together, describe the
   protocol and usage context for a revision of Internationalized Domain
   Names for Applications (IDNA), superseding the earlier version.  It
   describes the document collection and provides definitions and other
   material that are common to the set.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5890.

Klensin                      Standards Track                    [Page 1]
RFC 5890                    IDNA Definitions                 August 2010

Copyright Notice

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   document authors.  All rights reserved.

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   This document may contain material from IETF Documents or IETF
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   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Klensin                      Standards Track                    [Page 2]
RFC 5890                    IDNA Definitions                 August 2010

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  IDNA2008 . . . . . . . . . . . . . . . . . . . . . . . . .  4
       1.1.1.  Audiences  . . . . . . . . . . . . . . . . . . . . . .  4
       1.1.2.  Normative Language . . . . . . . . . . . . . . . . . .  5
     1.2.  Road Map of IDNA2008 Documents . . . . . . . . . . . . . .  5
   2.  Definitions and Terminology  . . . . . . . . . . . . . . . . .  6
     2.1.  Characters and Character Sets  . . . . . . . . . . . . . .  6
     2.2.  DNS-Related Terminology  . . . . . . . . . . . . . . . . .  6
     2.3.  Terminology Specific to IDNA . . . . . . . . . . . . . . .  7
       2.3.1.  LDH Label  . . . . . . . . . . . . . . . . . . . . . .  7
       2.3.2.  Terms for IDN Label Codings  . . . . . . . . . . . . . 11
         2.3.2.1.  IDNA-valid strings, A-label, and U-label . . . . . 11
         2.3.2.2.  NR-LDH Label . . . . . . . . . . . . . . . . . . . 13
         2.3.2.3.  Internationalized Domain Name and
                   Internationalized Label  . . . . . . . . . . . . . 13
         2.3.2.4.  Label Equivalence  . . . . . . . . . . . . . . . . 14
         2.3.2.5.  ACE Prefix . . . . . . . . . . . . . . . . . . . . 14
         2.3.2.6.  Domain Name Slot . . . . . . . . . . . . . . . . . 14
       2.3.3.  Order of Characters in Labels  . . . . . . . . . . . . 15
       2.3.4.  Punycode is an Algorithm, Not a Name or Adjective  . . 15
   3.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16
     4.1.  General Issues . . . . . . . . . . . . . . . . . . . . . . 16
     4.2.  U-label Lengths  . . . . . . . . . . . . . . . . . . . . . 16
     4.3.  Local Character Set Issues . . . . . . . . . . . . . . . . 17
     4.4.  Visually Similar Characters  . . . . . . . . . . . . . . . 17
     4.5.  IDNA Lookup, Registration, and the Base DNS
           Specifications . . . . . . . . . . . . . . . . . . . . . . 18