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Versions: 00 01 02                                                      
INTERNET-DRAFT                                                Hongbo Shi
draft-ietf-idn-iptr-02.txt                             Waseda University
17 May 2001                                             Jiang Ming Liang
Expires: 17 November 2001                                      i-DNS.net

              Internationalized PTR Resource Record (IPTR)

Status of this Memo

  This document is an Internet-Draft and is in full conformance with all
  provisions of Section 10 of RFC2026.

  Internet-Drafts are working documents of the Internet Engineering Task
  Force (IETF), its areas, and its working groups. Note that other
  groups may also distribute working documents as Internet-Drafts.

  Internet-Drafts are draft documents valid for a maximum of six months
  and may be updated, replaced, or obsoleted by other documents at any
  time. It is inappropriate to use Internet-Drafts as reference material
  or to cite them other than as "work in progress."

       The list of current Internet-Drafts can be accessed at

       The list of Internet-Draft Shadow Directories can be accessed at


  This draft attempts to address the problem of how an IP address SHOULD
  be properly mapped to a set of Internationalized Domain Names(IDNs).
  It is currently unspecified how a PTR record can be used for this
  purpose.  In addition, the syntax of the PTR resource record may be
  too restrictive for such a mapping in a more culturally meaningful
  context.  This document suggests a new TYPE called IPTR using EDNS0
  and a mechanism to combined language information with such a mapping.

1. Introduction

  Reverse mapping is a very important and essential function in the DNS.
  In today's Domain Name System, PTR RRs are used to support address-
  to-domain mappings. However, a current PTR RR does not provide support
  for proper address-to-IDN mappings, without certain modifications.
  Modifying the PTR structure will also affect the current reverse

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  mapping architecture. This document describes a new RR TYPE named IPTR
  to provide address-to-IDN mappings and it also specifies that on
  receiving of a IPTR query a name server should respond with all the
  corresponding IPTR RRs in one response. In short, "one IP several

1.1 Terminology

  and "MAY" in this document are to be interpreted as described in RFC
  2119 [RFC2119].

1.2 Background and Designs

  When Internationalized Domain Names come into wide use, an Internet
  host is likely to have domain names in different languages.  In
  today's Internet, even thought the [RFC2181] redefine the
  consideration of PTR, because of the design of the PTR mapping
  algorithm and implementation of most resolvers, IP address to domain
  names mapping is still limited to "one IP one domain name".

  For example, BIND treats PTRs specially so that the normal sorting
  preference (e.g. cyclic/random) doesn't apply. But as usual, "fixed"
  order is always used. So a client that is querying a BIND server and
  doesn't look beyond the first PTR RR, no matter how many times it
  queries the name. In other words, PTR RRset is different from A RRset,
  where the first record in the RRset might differ from query to query.

  This is more restrictive in a world of IDNs, for choosing some names
  in a particular language. Briefly, according to the use of PTR, it is
  no meaning of returning an IDN in an unknown language.

  The authors also believe that putting language information into
  address-to-name mappings will be benifitial to future applications.

  The design purpose of the IPTR RR type is to provide a mechanism that
  can map an IP address to the corresponding IDN per language. It also
  means that IPTR suggests a new mapping algorithm for the reverse
  mapping by using an language information.

  CNAME MUST continue to work for IPTR as it works now for PTR records.

  The behavior of a resolver on the use of IPTR will be specified in a
  seperate draft or a later version of this draft.

1.3 Functional Description

  DNS query and responses involving IPTR type MUST have the following

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       - When the QTYPE is IPTR, the corresponding IDNs SHOULD be
         returned in one response.

       - The characters in the label MUST be encoded using UTF-8

       - The entire label MUST be encoded EDNS [RFC2671].

       - An exceptional handling of PTR for the IDN is REQUIRED.

2. IPTR definition

  The structure of an IPTR RR is somewhat like the MX RR.  In addtion to
  the IP address in the IN-ADDR.ARPA domain and the domain name field
  (similar to a PTR RR), a new field called LANGUAGE has been defined.
  A domain name in an IPTR RR MUST be encoded in UTF8.  And IDN in this
  document MUST be NAMEPREPPED. [NAMEPREP] Below is an example of an
  IPTR RR:    IPTR  "LANGUAGE" "name-in-utf8"

  [RFC1766] describes the ISO 639/ISO 3166 conventions.  A language name
  is always written in lower case, while country codes are written in
  upper case. At here, the "LANGUAGE" field in an IPTR RR SHOULD be done
  in a case-insensitive manner and MUST follow the conventions defined
  in [RFC1766].

  For Example:            IPTR     "zh-CN"   "name-in-utf8"            IPTR     "zh-TW"   "name-in-utf8"            IPTR     "ja-JP"   "name-in-utf8"            IPTR     "ko-KR"   "name-in-utf8"

  The notion of canonical names and aliases described in 3.6.2
  [RFC1034], and 10.2 [RFC2181] MUST be preserved for IPTR record types.
  An IPTR RR SHOULD be limited to one primary IDN per LANGUAGE, similar
  to the a PTR RR.

3. IPTR on IPv6

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  Mapping IPv6 to IDNs can be similarly supported. This document recom-
  mands to continue using the IP6.INT domain defined in [RFC1886] for
  IPTR mappings.  For example, the lookup corresponding to the address
  4321:0:1:2:3:4:567:89ab would be:
  IPTR  "LANGUAGE" "name-in-utf8"

4. Packet format for IPTR

  EDNS0[RFC2671] is REQUIRED to implement IPTR.

       0                   1       2       3                   4
  bits 0 1 2 3 4 5 6 7 8 9 0 1...9 0...8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 ...
      |0 1|    ELT    |   LANGUAGE    |      Size     | IDN label... |

     LANGUAGE: An argument for IPTR to define the kind of language
               used in the following IDN label. The size is 2 octets.
     ELT: To be defined in [IDNE].

5. Coexistence

5.1 IDN Consideration

  IPTR described above is based on "a set of IDNs", strictly speaking, a
  set of canonical IDNs. On the other hand, confusion about IDN, such as
  "IDN MUST exist with ASCII domain name" has led to a belief that PTR
  record should have exactly RRs in its RRSet. In short, the phenomenon
  "IDN ONLY" will exist. Thus, the exceptional handling of PTR is

  On the other hand, IDN is still RECOMMENDED to exist with more than
  one ASCII domain name.

5.2 PTR Extension

  In the case of "IDN ONLY", if IPTR RR is not NULL, PTR RR MUST contain
  a domain name in ACE to coexist with those IDN unaware systems. Else a
  "Syntax Error" message SHOULD be sent back, when an administrator con-
  figures DNS zone files.

5.3 IPTR and PTR

  It is a kind of backward compatible handle for those IDN unaware sys-
  tems that can not provide the IPTR function. Besides, if a client can

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  not find the corresponding LANGUAGE IDN finally, then the correspond-
  ing PTR RR SHOULD be used as the answer.

6. IPTR query/response

  When the QTYPE is IPTR in a query, all of the corresponding IPTR RRs
  SHOULD be returned in one response. DNS messages are limited to 512
  octets or less in size when sent over UDP. Therefore, if all the RRs
  cannot fit in one UDP packet, this draft describe two solutions. One
  is for recent environment and the other is for the near future.

6.1 Transport

  Today, DNS queries and responses are carried in UDP datagrams or over
  TCP connections.[RFC1034] specifies, IPTR RRSet is RECOMMENDED to be
  returned in one response. The size of a DNS message could exceed 512
  octets, when multiple RRs are present. Therefore, this draft makes the
  two following recommendations.

     - "Use UDP first, if UDP is not large enough then change to TCP" is

       The server MUST send back the response with the TC bit set. Then
       the resolver SHOULD resend the query using TCP on server port
       53(decimal). This behavior is consistent with the current DNS
       specification [RFC1035].

     - In future, EDNS0 is REQUIRED to send large packets.

       Then, before a client send a query to ask for IPTR record, it
       MUST query the server whether it knows the EDNS0 first. If the
       server knows EDNS0, then the client MAY send the IPTR query.
       Else, unfortunally, the client MUST change the QTYPE to PTR.

       Hence, the size of the UDP payload is no longer limited to 512
       octets any more.

6.2 Standard sample

     A resolver who wants to find the IDNs corresponding to an IP
     address whould pursue a query of the form QTYPE=IPTR,
     QCLASS=IN, QNAME=, and would receive:

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      Header     | OPCODE=SQUERY, RESPONSE, AA                          |
      Question   | QNAME=,QCLASS=IN,QTYPE=IPTR     |
      Answer     | IPTR  "zh-CN" "name1-in-utf8"  |
                 | IPTR  "zh-TW" "name2-in-utf8"  |
                 | IPTR  "zh-JP" "name3-in-utf8"  |
                 | IPTR  "ko-KR" "name4-in-utf8"  |
      Authority  | ...                                                  |
      Additional | ...                                                  |

7. IPTR Usage

     The "foo1.example" in following samples MAY or MAY NOT be
     represented in the same characters.  IPTR  "zh-TW" "[foo1.example] in utf8"
                           IPTR  "zh-CN" "[foo1.example] in utf8"
                           IPTR  "ja-JP" "[foo1.example] in utf8"
                           IPTR  "ko-KR" "[foo1.example] in utf8"

     Moreover,  IPTR  "zh-TW" "[foo1.example] in utf8"
                           IPTR  "zh-TW" "[foo2.example] in utf8"
                           IPTR  "zh-CN" "[foo1.example] in utf8"
                           IPTR  "zh-CN" "[foo2.example] in utf8"
                           IPTR  "ja-JP" "[foo1.example] in utf8"
                           IPTR  "ja-JP" "[foo2.example] in utf8"
                           IPTR  "ko-KR" "[foo1.example] in utf8"
                           IPTR  "ko-KR" "[foo2.example] in utf8"

     will exist also. And "foo2.example" MUST be different from
     "foo1.example", if they are in signed with same LANGUAGE. Or a
     "Syntax Error" SHOULD be sent back, when an administrator config-
     ures the zone files. Furthermore "foo2.example" in the samples
     above MAY or MAY NOT be represented in the same characters.

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     Thus,  IPTR "zh-TW" "[samefoo.sample] in utf8"
                           IPTR "zh-TW" "[samefoo.sample] in utf8"

     occurs a "Syntax Error".

     And,  IPTR "zh-TW" "[samefoo.sample] in utf8"
                           IPTR "zh-TW" "[difffoo.sample] in utf8"
                           IPTR "zh-CN" "[samefoo.sample] in utf8"
                           IPTR "ja-JP" "[samefoo.sample] in utf8"
                           IPTR "ko-KR" "[samefoo.sample] in utf8"

     is allowed.

8. Changes

     Through the discussion on the IETF49 meeting in San Diego, we
     deleted the chapter "Open Issues" of our previous draft (version

     And,  IPTR "zh-TW" "[samefoo.sample] in utf8"
                           IPTR "zh-TW" "[difffoo.sample] in utf8"
                           IPTR "zh-CN" "[samefoo.sample] in utf8"
                           IPTR "ja-JP" "[samefoo.sample] in utf8"
                           IPTR "ko-KR" "[samefoo.sample] in utf8"

     is allowed.

8. Changes

     Through the discussion on the IETF49 meeting in San Diego, we
     deleted the chapter "Open Issues" of our previous draft (version


     [IDNREQ] Zita Wenzel & James Seng, "Requirements of International-
     ized Domain Names", draft-ietf-idn-requirements.

     [IDNE] Marc Blanchet & Paul Hoffman, "Internationalized domain
     names using EDNS", draft-ietf-idn-idne.

     [NAMEPREP] Paul Hoffman & Marc Blanchet, "Preparation of

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     Internationalized Host Names", draft-ietf-idn-nameprep.

     November 1987, RFC1034

     SPECIFICATION", November 1987, RFC1035

     [RFC1766] H. Alvestrand, "Tags for the Identification of
     Languages", March 1999, RFC 1766

     [RFC1886] S. Thomson, C. Huitema, "DNS Extensions to support IP
     version 6", December 1995, RFC1886

     [RFC2181] R. Elz, R. Bush, "Clarifications to the DNS Specifica-
     tion", July 1997, RFC2181

     [RFC2279] Francois Yergeau, "UTF-8, a transformation format of ISO
     10646", January 1998, RFC 2279.

     [RFC2671] Paul Vixie, "Extension Mechanisms for DNS (EDNS0)",
     August 1999, RFC 2671.

     [ISO 639] ISO 639:1988 (E/F) - Code for the representation of names
     of languages - The International Organization for Standardization,
     1st edition, 1988 17 pages Prepared by ISO/TC 37 - Terminology
     (principles and coordination).

     [ISO 3166] ISO 3166:1988 (E/F) - Codes for the representation of
     names of countries - The International Organization for Standardi-
     zation, 3rd edition, 1988-08-15.


     James Seng and Yoshiro Yoneya have given many comments in our e-
     mail discussions. Harald Alvestrand, Mark Davis have given many
     suggestions in the idn-wg mailing list discussions. And there are
     also a lot of people who have given us their comments in the idn-wg
     and BIND-user mailing list discussions.

Authors' Information

     Hongbo Shi
     Waseda University
     3-4-1 Okubo, Shinjyuku-ku
     Tokyo, 169-8555 Japan

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INTERNET-DRAFT   Internationalized PTR Resource Record       17 May 2001

     Jiang Ming Liang
     8 Temasek Boulevard
     #24-02 Suntec Tower Three
     Singapore 038988

Shi, Jiang                                                      [Page 9]