1. RFC 4713
Network Working Group                                             X. Lee
Request for Comments: 4713                                        W. Mao
Category: Informational                                            CNNIC
                                                                 E. Chen
                                                                  N. Hsu
                                                              J. Klensin
                                                            October 2006

Registration and Administration Recommendations for Chinese Domain Names

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).


   This RFC is not a candidate for any level of Internet Standard.  The
   IETF disclaims any knowledge of the fitness of this RFC for any
   purpose and in particular notes that the decision to publish is not
   based on IETF review for such things as security, congestion control,
   or inappropriate interaction with deployed protocols.  The RFC Editor
   has chosen to publish this document at its discretion.  Readers of
   this document should exercise caution in evaluating its value for
   implementation and deployment.  See RFC 3932 for more information.


   Many Chinese characters in common use have variants, which makes most
   of the Chinese Domain Names (CDNs) have at least two different forms.
   The equivalence between Simplified Chinese (SC) and Traditional
   Chinese (TC) characters is very important for CDN registration.  This
   memo builds on the basic concepts, general guidelines, and framework
   of RFC 3743 to specify proposed registration and administration
   procedures for Chinese domain names.  The document provides the
   information needed for understanding and using the tables defined in
   the IANA table registrations for Simplified and Traditional Chinese.

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RFC 4713        Recommendations for Chinese Domain Names    October 2006

Table of Contents

   1. Introduction ....................................................2
   2. Terminology .....................................................3
      2.1. Chinese Characters .........................................3
      2.2. Chinese Domain Name Label (CDNL) ...........................3
      2.3. Simplified Chinese Variant Table (SCVT) ....................4
      2.4. Traditional Chinese Variant Table (TCVT) ...................4
      2.5. Original Chinese Domain Name Label (OCDNL) .................4
   3. Procedure for Registration of Chinese Domain Name Labels ........4
      3.1. Terminology and Context ....................................4
      3.2. Procedure in Terms of the RFC 3743 Model ...................4
      3.3. RFC 3743 Optional Registry Processing ......................5
   4. Security Considerations .........................................5
   5. Acknowledgements ................................................6
   6. References ......................................................6
      6.1. Normative References .......................................6
      6.2. Informative References .....................................7

1.  Introduction

   With the standardization of Internationalized Domain Names for
   Application (IDNA, described in [RFC3490], [RFC3491], and [RFC3492]),
   internationalized domain names (IDNs), i.e., those that contain non-
   ASCII characters, are included in the DNS, and users can access the
   Internet with their native languages, most of which are not English.
   However, many languages have special requirements, which are not
   addressed in the IDNA RFCs.  One way to deal with some of the
   remaining issues involves grouping characters that could be confused
   together as "variants".  The variant approach is discussed in RFC
   4290 [RFC4290] and specifically for documents written in Chinese,
   Japanese, or Korean (CJK documents), in the so-called "JET
   Guidelines" RFC 3743 [RFC3743].  Readers of this document are assumed
   to be familiar with the concepts and terminology of the latter.  The
   guidelines specified in this document provide a set of specific
   tables and methods required to apply the JET Guidelines to Chinese
   characters.  For example, changes were made in the forms of a large
   number of Chinese characters during the last century to simplify
   writing and reading.  These "Simplified" characters have been adopted
   in some Chinese-speaking communities, while others continue to use
   the "Traditional" forms.  On the global Internet, if IDNA were used
   alone, there would be considerable potential for confusion if the two
   forms were not considered together.  Consequently, effective use of
   Chinese Domain Names (CDNs) requires variant equivalence, as
   described in RFC 3743, to handle character differences between
   Simplified and Traditional Chinese forms.

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RFC 4713        Recommendations for Chinese Domain Names    October 2006

   Chinese variant equivalence itself is very complicated in principle
   (please read [C2C] for further information).  When it comes to the
   usage of Chinese domain names, the basic requirement is to match the
   user perception of Chinese characters between Simplified Chinese (SC)
   and Traditional Chinese (TC) forms.  When users register SC or TC
   domain names, they will wish to obtain the other forms (Traditional
   or Simplified, respectively) as well, and expect others to be able to
   access the website or other resources in both forms.

   This document specifies a solution for Chinese domain name
   registration and administration that has been adopted and deployed by
   CNNIC (the top-level domain registry for "CN") and TWNIC (the top-
   level domain registry for "TW") to manage Simplified Chinese and
   Traditional Chinese domain name equivalence.  In the terminology of
   RFC 3743, this solution is based on Internationalized Domain Labels

2.  Terminology

   This document adopts the terminologies that are defined in RFC 3743.
   It is not possible to understand this document without first
   understanding the concepts and terminology or RFC 3743, including
   terminology introduced in its examples.  Additional terminology is
   defined later in this document.

2.1.  Chinese Characters

   This document suggests permitting only a subset of Chinese characters
   in Chinese Domain Names (CDNs) and hence in the DNS.  When this
   document discusses Chinese characters, it only refers to the subset
   of the characters in the first column of the current IANA
   registration tables for Chinese as discussed in Section 2.3 and
   Section 2.4.  These are defined, in detail, in [LVT-SC] and [LVT-TC].
   Of course, characters excluded from these tables are still valid
   Chinese characters.  However, this document strongly suggests that
   registries do not permit any registration of Chinese characters that
   are not listed in the tables.  The tables themselves will be updated
   in the future if necessary.

2.2.  Chinese Domain Name Label (CDNL)

   If an IDN label includes at least one Chinese character, it is called
   a Chinese Domain Name (CDN) Label.  CDN labels may contain characters
   from the traditional letter-digit-hyphen (LDH) set as well as Chinese

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2.3.  Simplified Chinese Variant Table (SCVT)

   Based on RFC 3743 [RFC3743], a language table for Simplified Chinese
   has been defined [LVT-SC].  It can be used for the registration of
   Simplified Chinese domain names.  The key feature of this table is
   that the preferred variant is the SC character, which is used by
   Chinese mainland users or defined in Chinese-related standards.

2.4.  Traditional Chinese Variant Table (TCVT)

   Similarly, a language table has been defined for Traditional Chinese
   [LVT-TC].  It is also based on the rules of RFC 3743.  It can be used
   for registration of Traditional Chinese domain names.  The preferred
   variant is the TC character, which is used by Taiwan users or defined
   in related standards.

2.5.  Original Chinese Domain Name Label (OCDNL)

   The Chinese Domain Name Label that users submit for registration.

3.  Procedure for Registration of Chinese Domain Name Labels

3.1.  Terminology and Context

   This document adopts the same procedure for Chinese Domain Name Label
   (CDNL) registration as the one defined for more general IDN labels in
   section 3.2.3 of RFC 3743 [RFC3743].  The terminology and notation
   used below, and the steps that are mentioned, derive from that
   document.  In particular, "CV" is the character variant associated
   with an input character ("IN") and a language table.  The language
   tables used here are those for Chinese as spoken and written in the
   Chinese mainland (ZH-CN) and on Taiwan (ZH-TW).  "PV" is the selected
   Preferred Variant.

3.2.  Procedure in Terms of the RFC 3743 Model

   The first column of the Simplified Chinese Variant Table (SCVT) is
   the same as the first column of the corresponding Traditional Chinese
   Variant Table (TCVT) and so are the third columns of both tables.
   Consequently, the CV(IN, ZH-CN) will be same as the CV(IN, ZH-TW)
   after Step 3; the PV(IN, ZH-CN) is in SC form, and the PV(IN, ZH-TW)
   is in TC form.  As a result, there will not be more than three
   records (i.e., for the original label (OCDNL), the Simplified Chinese
   (SC) form, and the Traditional Chinese (TC) form) to be added into
   the zone file after applying this procedure.  In other words, the
   procedure does not generate labels that contain a mixture of
   Simplified and Traditional Chinese as variants.

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RFC 4713        Recommendations for Chinese Domain Names    October 2006

   The set of languages associated with the input (IN) is both ZH-CN and
   ZH-TW by default. The procedure for CDNL registration uses the
   optional registry-defined rules provided in RFC 3743 for optional
   processing, with the understanding that the rules may vary for
   different registries supporting CDNs.  The motivation for such rules
   is described below.

   The preferred variant(s) is/are TC in TCVT, and SC in SCVT.  There
   may be more than one preferred variant for a given valid character.

3.3.  RFC 3743 Optional Registry Processing

   In actuality, while IDNA, and hence RFC 3743, process characters one
   at a time, the actual relationship between the valid code point and
   the preferred variant is contextual: whether one character can be
   substituted for another depends on the characters with which it is
   associated in a label or, more generally, in a phrase.  In
   particular, some of the preferred variants make no sense in
   combination with other characters; therefore, those combinations
   should not be added into the Zone file (described as "ZV" or zone
   variants in RFC 3743).  If desired, it should be possible to define
   and implement rules to reduce the preferred variant labels to only
   plausible ones.  This could be done, for example, with some
   artificial intelligence tools, or with feedback from the registrant,
   or with selection based on frequency of occurrence in other texts.
   To illustrate one possibility, the OCDNL could be required to be TC-
   only or SC-only, and if there is more than one preferred variant, the
   OCDNL will be used as the PV, instead of the PV produced by the

   To reemphasize, the tables in [LVT-SC] and [LVT-TC] follow the table
   format and terminologies defined in [RFC3743].  If one intends to
   implement Chinese domain name registrations based on these two tables
   or ones similar to them, a complete understanding of RFC 3743 is
   needed for the proper use of those tables.

4.  Security Considerations

   This document is subject to the same security considerations as RFC
   3743, which defines the table formats and operations.  As with that
   base document, part of its intent is to reduce the security problems
   that might be caused by confusion among characters with similar
   appearances or meanings.  While it will not introduce any additional
   security issues, additional registration restrictions such as those
   outlined in Section 3 may further reduce potential problems.

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5.  Acknowledgements

   Thanks to these people for their suggestions and for their efforts to
   bring this tough work to conclusion and to promote the results: WANG
   YanFeng, Ai-Chin LU, Shian-Shyong TSENG, QIAN HuaLin, and Li-Ming

   The authors especially thank Joe ZHANG and XiaoMing WANG for their
   outstanding contributions on SCVT in [LVT-SC].  Also, thanks to Kenny
   HUANG, Zheng-Wei LIN, Shi-Xiong TSENG, Lie-Neng WU, Cheng-Wu PAN,
   Lin-Mei WEI, and Qi-Qing HSU for their efforts and contributions on
   editing the TCVT in [LVT-TC].  These experts provided basic materials
   or gave very crucial suggestions and principles to accomplish these
   two variant tables.

   The authors also gratefully acknowledge the contributions of those
   who commented and made suggestions on this document, including James
   SENG, and other JET members.

6.  References

6.1.  Normative References

   [LVT-SC]   QIAN, H. and X. LEE, ".CN Chinese Character Table", IANA
              IDN Languages Tables, March 2005.

   [LVT-TC]   LU, A., ".TW Traditional Chinese Character Table", IANA
              IDN Languages Tables, March 2005.

   [RFC3490]  Faltstrom, P., Hoffman, P., and A. Costello,
              "Internationalizing Domain Names in Applications (IDNA)",
              RFC 3490, March 2003.

   [RFC3491]  Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
              Profile for Internationalized Domain Names (IDN)", RFC
              3491, March 2003.

   [RFC3492]  Costello, A., "Punycode: A Bootstring encoding of Unicode
              for Internationalized Domain Names in Applications
              (IDNA)", RFC 3492, March 2003.

   [RFC3743]  Konishi, K., Huang, K., Qian, H., and Y. Ko, "Joint
              Engineering Team (JET) Guidelines for Internationalized
              Domain Names (IDN) Registration and Administration for
              Chinese, Japanese, and Korean", RFC 3743, April 2004.

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6.2.  Informative References

   [C2C]      Halpern, J. and J. Kerman, "Pitfalls and Complexities of
              Chinese to Chinese Conversion", International Unicode
              Conference (14th) in Boston, March 1999.

   [RFC4290]  Klensin, J., "Suggested Practices for Registration of
              Internationalized Domain Names (IDN)", RFC 4290, December

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Authors' Addresses

   LEE Xiaodong
   CNNIC, No.4 South 4th Street, Zhongguancun
   Beijing  100080
   Phone: +86 10 58813020

   EMail: lee@cnnic.cn
   URI:   http://www.cnnic.cn

   MAO Wei
   CNNIC, No.4 South 4th Street, Zhongguancun
   Beijing  100080

   Phone: +86 10 58813055
   EMail: mao@cnnic.cn
   URI:   http://www.cnnic.cn

   Erin CHEN
   TWNIC, 4F-2, No. 9, Sec. 2, Roosevelt Rd.
   Taipei  100
   Phone: +886 2 23411313

   EMail: erin@twnic.net.tw
   URI:   http://www.twnic.net.tw

   Nai-Wen HSU
   TWNIC, 4F-2, No. 9, Sec. 2, Roosevelt Rd.
   Taipei  100

   Phone: +886 2 23411313
   EMail: snw@twnic.net.tw
   URI:   http://www.twnic.net.tw

   1770 Massachusetts Ave, #322
   Cambridge, MA  02140

   Phone: +1 617 491 5735
   EMail: john+ietf@jck.com

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  1. RFC 4713