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Versions: 00 01 02                                                      
INTERNET-DRAFT                                                Hongbo Shi
draft-ietf-idn-iptr-00.txt                             Waseda University
                                                         Jiang Ming Liang
                                                                 Sep 2000

               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 combind 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.

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   Modifying the PTR structure will also affect the current reverse
   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.  This document also specifies
   that an IPTR RR SHOULD refer to one primary iDN per language only.

1.1 Terminology

   The key words "MUST", "SHALL", "REQUIRED", "SHOULD", "RECOMMENDED",
   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, because of the design of the PTR record and
   implementation of most resolvers, IP address to domain names mapping
   is limited to "one IP one domain name", the primary domain name of the
   host. This is more restrictive in a world of iDNs, for choosing one
   name in one particular language as the primary could have cultural
   implications.  The authors also believe that putting language
   information into address-to-name mappings will be benifitial to future

   The design purpose of the IPTR RR type is to provide a mechanism that
   can map an IP address to all of the corresponding iDNs per language.

   CNAME MUST continue to work for IPTR as it works now for PTR records.
   An IPTR RR SHOULD be limited to one primary iDN per language.

   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

      - 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

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

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.  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.  The "language" field in an IPTR RR MUST follow the con-
   ventions 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]
   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

   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.

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      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 languages
              used in the following IDN label. The size is 2 octets.
    ELT:   To be defined.

5. 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.

5.1 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

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

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

5.2 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  "ja-jp" "name3-in-utf8"  |
             | IPTR  "ko-kr" "name4-in-utf8"  |
  Authority  | ...                                                  |
  Additional | ...                                                  |

6 Open Issues

      1.   API issues on the resolver side.

      2.   the granularity of the language info. (per domain name?  per
           label? within label?)

           Practically, we believe it is enough for the iPTR info to be
           expressed as |01|ELT|language|size|utf8|size|utf8|...|, mean-
           ing the LANGUAGE TAG is used to define the language of the
           Fully Quantified Domain Name.  However, FQDNs could still
           exist in the form of "English-in-utf8.Chinese-in-utf8.English-
           in-utf8."  And more than 1 language can exist in the same
           label.  Should such level of detailedness be supported?  Or a
           simple meta-type like "mixed-language" is enough?

      3.   If language info should somehow be relatable to an iDN
           itself(nothing to do with PTR...) and how?

           As a suggestion, if a new RR TYPE INAME is established to
           relate iDN to current domain name, there will be two merit.
           One is we don't to do anything with PTR. Second is if we cache
           the INAME RRs to the DNS caches, then it can reduce the upper
           layer name servers' jobs. Actually, the feature of the new RR
           TYPE is quite similar to CNAME and DNAME, meaning name-to-

           FQIDN: Fully Qualified Internationalized Domain Name.

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           Then the INAME RR is expressed following:

             iDN   INAME   traditional domain name

           About the first merit, When the client looks up an IP address
           to iDNs then the server will reponse not only corresponding
           PTR RR but corresponding INAME RRs to the client.  Further-
           more, the problem in LANGUAGE TAG can be avoided.

           For example:
       PTR      traditional-domain-name
             iDN-1                   INAME    traditional-domain-name
             iDN-2                   INAME    traditional-domain-name

           About the second merit, INAME is not only can be used in
           address-to-name mapping but name-to-address mapping.

           For example:
             traditional domain name  IN  A   host address
             iDN-1                    INAME   traditional-domain-name
             iDN-2                    INAME   traditional-domain-name

           When the client looks up an iDN or traditional domain name  to
           its corresponding IP address, if the server reponses not only
           A RR but INAME RRs to the client. And the client cache these
           RRs to its DNS cache.  Then the next time, maybe some queries
           can be resolved in DNS cache.


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

November 1987, RFC1034

TION", 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

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

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[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 edi-
tion, 1988 17 pages Prepared by ISO/TC 37 - Terminology (principles and

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


James Seng has given many comments in our e-mail discussions.

Authors' Information

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

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