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Versions: 00 01 rfc2247                                  Standards Track
Network Working Group                                           S. Kille
INTERNET-DRAFT                                                Isode Ltd.
Obsoletes: RFC 1279                                              M. Wahl
                                                     Critical Angle Inc.
Expires in six months from                              February 6, 1997
Intended Category: Standards Track

           An Approach for Using Domains in LDAP Distinguished Names

Status of this Memo

   This document is an Internet-Draft.  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
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   or to cite them other than as "work in progress."

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1. Abstract

   The Lightweight Directory Access Protocol (LDAP) uses X.500-compatible
   distinguished names for providing unique identification of entries.
   distinguished names in currently-deployed X.500 directories have the
   properties that they are descriptive, hierarchical, and follow common
   organizational models.  However, there is not today a registration
   mechanism to permit individuals and organizations to obtain distinguished
   names, regardless of their physical location.

   This document defines a mechanism by which a name registered with the
   Internet Domain Name Service [1], for which there are active registration
   services, can be represented as a distinguished name so that it may be
   used with the LDAP protocol.  This is not intended to have LDAP replace
   the DNS protocol, but to permit further deployment of LDAP into
   organizations connected to the Internet.

   This algorithm automatically assigns a distinguished name to any
   enterprise which has obtained a domain name for use in the Internet.
   This distinguished name may be used as a prefix for their names of
   entries in that enterprise.

   This document does not define how to represent objects which do not have
   domain names.  Several RFCs, such as [3] and [4], and more recent
   documents provide additional guidance on representing and structuring
   information in these entries.  Nor does this document define the procedure
   to locate an enterprises' LDAP directory server, given their domain name.
   Such as procedure may be defined in future RFCs.

Kille, Wahl                                                          Page 1

INTERNET-DRAFT                  Domains in LDAP DNs            February 1997

2. Introduction to Domain Names and Distinguished Names

   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".

   The X.500 Directory provides 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.

   An example distinguished name represented in the LDAP string format [2]
   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.

3. Mapping Domain Names into Distinguished Names

   This section defines a subset of the X.500 naming structure for use in
   representing names allocated in the Internet Domain Name System.  It is
   expected that it would be possible to algorithmically transform any
   Internet domain name into a distinguished name, and to be able to convert
   such a name back into a domain name.

   The algorithm for transforming a domain name is to begin with an empty
   DN and then attach RDNs for each component of the domain, most significant
   first.  Each of these RDNs have a single AttributeTypeAndValue, where the
   type is DC and the value is an IA5 string containing the component.

   Thus the domain name "CS.UCL.AC.UK" can be transformed into
   and similarly "11.168.192.IN-ADDR.ARPA" to

   X.500 distinguished names in which there are one or more RDNs, all with
   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 and Object Class Definitions

   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 'IA5String' 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.

Kille, Wahl                                                          Page 2

INTERNET-DRAFT                  Domains in LDAP DNs            February 1997

   Objects with names derived from their domain name using the algorithm of
   section 3 may be represented as an entry in the directory.  This allows
   information (attributes) to be associated with that entry.  The entry
   will have as its structural object class the "domain" object class, or
   a subclass of "domain".

    ( 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.
   The semantics of these attributes are defined in X.520 [5].

   The DC attribute is used for naming entries of the domain class.  This is
   reflected by the following name form rule.

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

   If it is desired to be able to store or retrieve DNS record attributes
   of the domain via LDAP, the dNSDomain object class can be used as well.
   This object class should only be present in the entry if the DNS records
   are listed as attributes.

    ( 0.9.2342.19200300.100.4.15 NAME 'dNSDomain' SUP domain STRUCTURAL
      MAY dNSRecord )

   The dNSRecord attribute may take one or more values.

    ( 0.9.2342.19200300.100.1.26 NAME 'dNSRecord'
      EQUALITY caseExactIA5Match SYNTAX 'IA5String' )

5. Relationship between LDAP and DNS Directories

   Implementations should be aware of the differences in deployment between
   LDAP and DNS directories.

   To effectively search the entries in an LDAP service, it is necessary to
   know the base object of the entries held by that service.  Generally that
   base object will be in one of the naming contexts in the LDAP service.

   While most objects with domain names are listed in an DNS-capable
   directory system, it is currently expected that only a small subset of
   the objects with domain names will be listed in LDAP-capable directories.

Kille, Wahl                                                          Page 3

INTERNET-DRAFT                  Domains in LDAP DNs            February 1997

   Furthermore, there may not necessarily be exactly one LDAP-capable
   directory listing service for many top-level domains (such as ".COM" or
   ".US").  There many be multiple distinct entries with the same name held
   by different, disconnected directory services. There may be some objects
   accessible in a directory service, for which the superior objects are not
   held by any directory server.

   LDAP client implementations should not assume that subtree searches may
   be based at the root of the DIT, or at immediately subordinate entries.
   Nor should LDAP client implementations assume that a name transformed from
   a contacted server's domain name will be a context prefix held by that
   server.  If the client and server both implement LDAP version 3, the
   client may interrogate the server for the naming contexts it holds.

6. References

   [1] P. Mockapetris. Domain names - concepts and facilities.
       RFC 1034, November 1987.

   [2] S. Kille, M.Wahl.  Lightweight Directory Access Protocol (v3):
       UTF-8 String Representation of Distinguished Names.
       INTERNET DRAFT draft-ietf-asid-ldapv3-dn-00.txt. July 1996.

   [3] P. Barker, S. Kille, T. Lenggenhager, "Naming and Structuring
       Guidelines for X.500 Directory Pilots". RFC 1617 May 1994.

   [4] B. Jennings, "Building an X.500 Directory Service in the US",
       RFC 1943, May 1996.

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.

8. Author's Address

   Steve Kille
   Isode Ltd.
   The Dome
   The Square
   Richmond, Surrey
   TW9 1DT
   Phone:  +44-181-332-9091
   EMail:  S.Kille@ISODE.COM

   Mark Wahl
   Critical Angle Inc.
   4815 W. Braker Lane #502-385
   Austin, TX 78759
   EMail:  M.Wahl@critical-angle.com

Kille, Wahl                                                          Page 4