    Network Working Group                                           S. Kille
    Request for Comments: 2247                                    Isode Ltd.
    Category: Standards Track                                        M. Wahl
                                                         Critical Angle Inc.
                                                                 A. Grimstad
                                                                        AT&T
                                                                    R. Huber
                                                                        AT&T
                                                                 S. Sataluri
                                                                        AT&T
                                                                January 1998

                Using Domains in LDAP/X.500 Distinguished Names

    Status of this Memo

       This document specifies an Internet standards track protocol for the
       Internet community, and requests discussion and suggestions for
       improvements.  Please refer to the current edition of the "Internet
       Official Protocol Standards" (STD 1) for the standardization state
       and status of this protocol.  Distribution of this memo is unlimited.

    Copyright Notice

       Copyright (C) The Internet Society (1998).  All Rights Reserved.

    1. Abstract

       The Lightweight Directory Access Protocol (LDAP) uses X.500-
       compatible distinguished names [3] for providing unique
       identification of entries.

       This document defines an algorithm by which a name registered with
       the Internet Domain Name Service [2] can be represented as an LDAP
       distinguished name.

    2. Background

       The Domain (Nameserver) System (DNS) provides a hierarchical resource
       labeling system.   A name is made up of an ordered set of components,
       each of which are short strings. An example domain name with two
       components would be "CRITICAL-ANGLE.COM".

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    RFC 2247              Using Domains in LDAP/X.500           January 1998

       LDAP-based directories provide a more general hierarchical naming
       framework. A primary difference in specification of distinguished
       names from domain names is that each component of an distinguished
       name has an explicit attribute type indication.

       X.500 does not mandate any particular naming structure.  It does
       contain suggested naming structures which are based on geographic and
       national regions, however there is not currently an established
       registration infrastructure in many regions which would be able to
       assign or ensure uniqueness of names.

       The mechanism described in this document automatically provides an
       enterprise a distinguished name for each domain name it has obtained
       for use in the Internet.  These distinguished names may be used to
       identify objects in an LDAP directory.

       An example distinguished name represented in the LDAP string format
       [3] is "DC=CRITICAL-ANGLE,DC=COM".  As with a domain name, the most
       significant component, closest to the root of the namespace, is
       written last.

       This document does not define how to represent objects which do not
       have domain names.  Nor does this document define the procedure to
       locate an enterprise's LDAP directory server, given their domain
       name.  Such procedures may be defined in future RFCs.

    3. Mapping Domain Names into Distinguished Names

       This section defines a subset of the possible distinguished name
       structures for use in representing names allocated in the Internet
       Domain Name System.  It is possible to algorithmically transform any
       Internet domain name into a distinguished name, and to convert these
       distinguished names back into the original domain names.

       The algorithm for transforming a domain name is to begin with an
       empty distinguished name (DN) and then attach Relative Distinguished
       Names (RDNs) for each component of the domain, most significant (e.g.
       rightmost) first. Each of these RDNs is a single
       AttributeTypeAndValue, where the type is the attribute "DC" and the
       value is an IA5 string containing the domain name component.

       Thus the domain name "CS.UCL.AC.UK" can be transformed into

            DC=CS,DC=UCL,DC=AC,DC=UK

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    RFC 2247              Using Domains in LDAP/X.500           January 1998

       Distinguished names in which there are one or more RDNs, all
       containing only the attribute type DC, can be mapped back into domain
       names. Note that this document does not define a domain name
       equivalence for any other distinguished names.

    4. Attribute Type Definition

       The DC (short for domainComponent) attribute type is defined as
       follows:

        ( 0.9.2342.19200300.100.1.25 NAME 'dc' EQUALITY caseIgnoreIA5Match
         SUBSTR caseIgnoreIA5SubstringsMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 SINGLE-VALUE )

       The value of this attribute is a string holding one component of a
       domain name.  The encoding of IA5String for use in LDAP is simply the
       characters of the string itself.  The equality matching rule is case
       insensitive, as is today's DNS.

    5. Object Class Definitions

       An object with a name derived from its domain name using the
       algorithm of section 3 is represented as an entry in the directory.
       The "DC" attribute is present in the entry and used as the RDN.

       An attribute can only be present in an entry held by an LDAP server
       when that attribute is permitted by the entry's object class.

       This section defines two object classes.  The first, dcObject, is
       intended to be used in entries for which there is an appropriate
       structural object class.  For example, if the domain represents a
       particular organization, the entry would have as its structural
       object class 'organization', and the 'dcObject' class would be an
       auxiliary class.  The second, domain, is a structural object class
       used for entries in which no other information is being stored. The
       domain object class is typically used for entries that are
       placeholders or whose domains do not correspond to real-world
       entities.

    5.1. The dcObject object class

       The dcObject object class permits the dc attribute to be present in
       an entry.  This object class is defined as auxiliary, as it would
       typically be used in conjunction with an existing structural object
       class, such as organization, organizationalUnit or locality.

       The following object class, along with the dc attribute, can be added
       to any entry.

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       ( 1.3.6.1.4.1.1466.344 NAME 'dcObject' SUP top AUXILIARY MUST dc )

       An example entry would be:

       dn: dc=critical-angle,dc=com
       objectClass: top
       objectClass: organization
       objectClass: dcObject
       dc: critical-angle
       o: Critical Angle Inc.

    5.2. The domain object class

       If the entry does not correspond to an organization, organizational
       unit or other type of object for which an object class has been
       defined, then the "domain" object class can be used.  The "domain"
       object class requires that the "DC" attribute be present, and permits
       several other attributes to be present in the entry.

       The entry will have as its structural object class the "domain"
       object class.

    ( 0.9.2342.19200300.100.4.13 NAME 'domain' SUP top STRUCTURAL
     MUST dc
     MAY ( userPassword $ searchGuide $ seeAlso $ businessCategory $
     x121Address $ registeredAddress $ destinationIndicator $
     preferredDeliveryMethod $ telexNumber $ teletexTerminalIdentifier $
     telephoneNumber $ internationaliSDNNumber $ facsimileTelephoneNumber $
     street $ postOfficeBox $ postalCode $ postalAddress $
     physicalDeliveryOfficeName $ st $ l $ description $ o $
     associatedName ) )

       The optional attributes of the domain class are used for describing
       the object represented by this domain, and may also be useful when
       searching.  These attributes are already defined for use with LDAP
       [4].

       An example entry would be:

       dn: dc=tcp,dc=critical-angle,dc=com
       objectClass: top
       objectClass: domain
       dc: tcp
       description: a placeholder entry used with SRV records

       The DC attribute is used for naming entries of the domain class, and
       this can be represented in X.500 servers by the following name form
       rule.

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    RFC 2247              Using Domains in LDAP/X.500           January 1998

        ( 1.3.6.1.4.1.1466.345 NAME 'domainNameForm' OC domain MUST ( dc ) )

    6. References

       [1] The Directory: Selected Attribute Types. ITU-T Recommendation
           X.520, 1993.

       [2] Mockapetris, P., " Domain Names - Concepts and Facilities,"
           STD 13, RFC 1034, November 1987.

       [3] Kille, S., and M. Wahl, " Lightweight Directory Access Protocol
           (v3): UTF-8 String Representation of Distinguished Names", RFC
           2253, December 1997.

       [4] Wahl, M., "A Summary of the X.500(96) User Schema for use with
           LDAP", RFC 2256, December 1997.

    7. Security Considerations

       This memo describes how attributes of objects may be discovered and
       retrieved.  Servers should ensure that an appropriate security policy
       is maintained.

       An enterprise is not restricted in the information which it may store
       in DNS or LDAP servers.  A client which contacts an untrusted server
       may have incorrect or misleading information returned (e.g. an
       organization's server may claim to hold naming contexts representing
       domain names which have not been delegated to that organization).

    8. Authors' Addresses

       Steve Kille
       Isode Ltd.
       The Dome
       The Square
       Richmond, Surrey
       TW9 1DT
       England

       Phone:  +44-181-332-9091
       EMail:  S.Kille@ISODE.COM

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    RFC 2247              Using Domains in LDAP/X.500           January 1998

       Mark Wahl
       Critical Angle Inc.
       4815 W. Braker Lane #502-385
       Austin, TX 78759
       USA

       Phone:  (1) 512 372 3160
       EMail:  M.Wahl@critical-angle.com

       Al Grimstad
       AT&T
       Room 1C-429, 101 Crawfords Corner Road
       Holmdel, NJ 07733-3030
       USA

       EMail: alg@att.com

       Rick Huber
       AT&T
       Room 1B-433, 101 Crawfords Corner Road
       Holmdel, NJ 07733-3030
       USA

       EMail: rvh@att.com

       Sri Sataluri
       AT&T
       Room 4G-202, 101 Crawfords Corner Road
       Holmdel, NJ 07733-3030
       USA

       EMail: sri@att.com

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    9.  Full Copyright Statement

       Copyright (C) The Internet Society (1998).  All Rights Reserved.

       This document and translations of it may be copied and furnished to
       others, and derivative works that comment on or otherwise explain it
       or assist in its implementation may be prepared, copied, published
       and distributed, in whole or in part, without restriction of any
       kind, provided that the above copyright notice and this paragraph are
       included on all such copies and derivative works.  However, this
       document itself may not be modified in any way, such as by removing
       the copyright notice or references to the Internet Society or other
       Internet organizations, except as needed for the purpose of
       developing Internet standards in which case the procedures for
       copyrights defined in the Internet Standards process must be
       followed, or as required to translate it into languages other than
       English.

       The limited permissions granted above are perpetual and will not be
       revoked by the Internet Society or its successors or assigns.

       This document and the information contained herein is provided on an
       "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
       TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
       BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
       HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
       MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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