Review and Recommendations for Internationalized Domain Names (IDNs)
RFC 4690

Document Type RFC - Informational (September 2006; Errata)
Last updated 2016-12-29
Stream IAB
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Network Working Group                                         J. Klensin
Request for Comments: 4690                                  P. Faltstrom
Category: Informational                                    Cisco Systems
                                                                 C. Karp
                                       Swedish Museum of Natural History
                                                                     IAB
                                                          September 2006

  Review and Recommendations for Internationalized Domain Names (IDNs)

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This note describes issues raised by the deployment and use of
   Internationalized Domain Names.  It describes problems both at the
   time of registration and for use of those names in the DNS.  It
   recommends that IETF should update the RFCs relating to IDNs and a
   framework to be followed in doing so, as well as summarizing and
   identifying some work that is required outside the IETF.  In
   particular, it proposes that some changes be investigated for the
   Internationalizing Domain Names in Applications (IDNA) standard and
   its supporting tables, based on experience gained since those
   standards were completed.

Table of Contents

   1. Introduction ....................................................3
      1.1. The Role of IDNs and This Document .........................3
      1.2. Status of This Document and Its Recommendations ............4
      1.3. The IDNA Standard ..........................................4
      1.4. Unicode Documents ..........................................5
      1.5. Definitions ................................................5
           1.5.1. Language ............................................6
           1.5.2. Script ..............................................6
           1.5.3. Multilingual ........................................6
           1.5.4. Localization ........................................7
           1.5.5. Internationalization ................................7

Klensin, et al.              Informational                      [Page 1]
RFC 4690                 IAB -- IDN Next Steps            September 2006

      1.6. Statements and Guidelines ..................................7
           1.6.1. IESG Statement ......................................8
           1.6.2. ICANN Statements ....................................8
   2. General Problems and Issues ....................................11
      2.1. User Conceptions, Local Character Sets, and Input issues ..11
      2.2. Examples of Issues ........................................13
           2.2.1. Language-Specific Character Matching ...............13
           2.2.2. Multiple Scripts ...................................13
           2.2.3. Normalization and Character Mappings ...............14
           2.2.4. URLs in Printed Form ...............................16
           2.2.5. Bidirectional Text .................................17
           2.2.6. Confusable Character Issues ........................17
           2.2.7. The IESG Statement and IDNA issues .................19
   3. Migrating to New Versions of Unicode ...........................20
      3.1. Versions of Unicode .......................................20
      3.2. Version Changes and Normalization Issues ..................21
           3.2.1. Unnormalized Combining Sequences ...................21
           3.2.2. Combining Characters and Character Components ......22
           3.2.3. When does normalization occur? .....................23
   4. Framework for Next Steps in IDN Development ....................24
      4.1. Issues within the Scope of the IETF .......................24
           4.1.1. Review of IDNA .....................................24
           4.1.2. Non-DNS and Above-DNS Internationalization
                  Approaches .........................................25
           4.1.3. Security Issues, Certificates, etc. ................25
           4.1.4. Protocol Changes and Policy Implications ...........27
           4.1.5. Non-US-ASCII in Local Part of Email Addresses ......27
           4.1.6. Use of the Unicode Character Set in the IETF .......27
      4.2. Issues That Fall within the Purview of ICANN ..............28
           4.2.1. Dispute Resolution .................................28
           4.2.2. Policy at Registries ...............................28
           4.2.3. IDNs at the Top Level of the DNS ...................29
   5. Specific Recommendations for Next Steps ........................29
      5.1. Reduction of Permitted Character List .....................29
           5.1.1. Elimination of All Non-Language Characters .........30
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