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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  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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  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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   ( 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:  [email protected]










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

  Phone:  (1) 512 372 3160
  EMail:  [email protected]


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

  EMail: [email protected]


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

  EMail: [email protected]


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

  EMail: [email protected]
















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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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