Network Working Group                                        K. Zeilenga
Request for Comments: 3674                           OpenLDAP Foundation
Category: Standards Track                                  December 2003


  Feature Discovery in Lightweight Directory Access Protocol (LDAP)

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 (2003).  All Rights Reserved.

Abstract

  The Lightweight Directory Access Protocol (LDAP) is an extensible
  protocol with numerous elective features.  This document introduces a
  general mechanism for discovery of elective features and extensions
  which cannot be discovered using existing mechanisms.

1.  Background and Intended Use

  The Lightweight Directory Access Protocol (LDAP) [RFC3377] is an
  extensible protocol with numerous elective features.  LDAP provides
  mechanisms for a client to discover supported protocol versions,
  controls, extended operations, Simple Authentication and Security
  Layer (SASL) mechanisms, and subschema information.  However, these
  mechanisms are not designed to support general feature discovery.

  This document describes a simple, general-purpose mechanism which
  clients may use to discover the set of elective features supported by
  a server.  For example, this mechanism could be used by a client to
  discover whether or not the server supports requests for all
  operational attributes, e.g., "+" [RFC3673].  As another example,
  this mechanism could be used to discover absolute true, e.g., "(&)"
  and false, e.g., "(|)", search filters [T-F] support.

  This document extends the LDAP Protocol Mechanism registry [RFC3383]
  to support registration of values of the supportedFeatures attribute.
  This registry is managed by the Internet Assigned Numbers Authority
  (IANA).




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  Schema definitions are provided using LDAP description formats
  [RFC2252].  Definitions provided here are formatted (line wrapped)
  for readability.

  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
  "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
  document are to be interpreted as described in BCP 14 [RFC2119].

2.  Discovery of supported features

  Each elective feature whose support may be discovered SHALL be
  identified by an Object Identifier (OID).  A server advertises its
  support for a given feature by providing the OID associated with the
  feature as a value of the 'supportedFeatures' attribute held in the
  root DSE.  A client may examine the values of this attribute to
  determine if a particular feature is supported by the server.  A
  client MUST ignore values it doesn't recognize as they refer to
  elective features it doesn't implement.

  Features associated with Standard Track protocol mechanisms MUST be
  registered.  Features associated with other protocol mechanisms
  SHOULD be registered.  Procedures for registering protocol mechanisms
  are described in BCP 64 [RFC3383].  The word "Feature" should be
  placed in the usage field of the submitted LDAP Protocol Mechanism
  template.

  The 'supportedFeatures' attribute type is described as follows:

     ( 1.3.6.1.4.1.4203.1.3.5
       NAME 'supportedFeatures'
       DESC 'features supported by the server'
       EQUALITY objectIdentifierMatch
       SYNTAX 1.3.6.1.4.1.1466.115.121.1.38
       USAGE dSAOperation )

  Servers MUST be capable of recognizing this attribute type by the
  name 'supportedFeatures'.  Servers MAY recognize the attribute type
  by other names.

3.  Security Considerations

  As rogue clients can discover features of a server by other means
  (such as by trial and error), this feature discovery mechanism is not
  believed to introduce any new security risk to LDAP.







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4.  IANA Considerations

4.1.  Registration of Features as Protocol Mechanisms

  Future specifications detailing LDAP features are to register each
  feature as a LDAP Protocol Mechanism per guidance given in BCP 64
  [RFC3383].  A usage of "Feature" in a Protocol Mechanism registration
  template indicates that the value to be registered is associated with
  an LDAP feature.

4.2.  Registration of the supportedFeatures descriptor

  The IANA has registered the LDAP 'supportedFeatures' descriptor.  The
  following registration template is suggested:

     Subject: Request for LDAP Descriptor Registration
     Descriptor (short name): supportedFeatures
     Object Identifier: 1.3.6.1.4.1.4203.1.3.5
     Person & email address to contact for further information:
         Kurt Zeilenga <[email protected]>
     Usage: Attribute Type
     Specification: RFC 3674
     Author/Change Controller: IESG

  This OID was assigned [ASSIGN] by OpenLDAP Foundation under its IANA
  assigned private enterprise allocation [PRIVATE] for use in this
  specification.

5.  Acknowledgment

  This document is based upon input from the IETF LDAPEXT working
  group.

6.  Intellectual Property Statement

  The IETF takes no position regarding the validity or scope of any
  intellectual property or other rights that might be claimed to
  pertain to the implementation or use of the technology described in
  this document or the extent to which any license under such rights
  might or might not be available; neither does it represent that it
  has made any effort to identify any such rights.  Information on the
  IETF's procedures with respect to rights in standards-track and
  standards-related documentation can be found in BCP-11.  Copies of
  claims of rights made available for publication and any assurances of
  licenses to be made available, or the result of an attempt made to
  obtain a general license or permission for the use of such
  proprietary rights by implementors or users of this specification can
  be obtained from the IETF Secretariat.



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  The IETF invites any interested party to bring to its attention any
  copyrights, patents or patent applications, or other proprietary
  rights which may cover technology that may be required to practice
  this standard.  Please address the information to the IETF Executive
  Director.

7.  References

7.1.  Normative References

  [RFC2119]     Bradner, S., "Key words for use in RFCs to Indicate
                Requirement Levels", BCP 14, RFC 2119, March 1997.

  [RFC2252]     Wahl, M., Coulbeck, A., Howes, T. and S. Kille,
                "Lightweight Directory Access Protocol (v3):  Attribute
                Syntax Definitions", RFC 2252, December 1997.

  [RFC3377]     Hodges, J. and R. Morgan, "Lightweight Directory Access
                Protocol (v3): Technical Specification", RFC 3377,
                September 2002.

  [RFC3383]     Zeilenga, K., "Internet Assigned Numbers Authority
                (IANA) Considerations for Lightweight Directory Access
                Protocol (LDAP)", BCP 64, RFC 3383, September 2002.

7.2.  Informative References

  [RFC3673]     Zeilenga, K., "Lightweight Directory Access Protocol
                version 3 (LDAPv3): All Operational Attributes", RFC
                3673, December 2003.

  [T-F]         Zeilenga, K., "LDAP True/False Filters", Work in
                Progress.

  [ASSIGN]      OpenLDAP Foundation, "OpenLDAP OID Delegations",
                http://www.openldap.org/foundation/oid-delegate.txt.

  [PRIVATE]     IANA, "Private Enterprise Numbers",
                http://www.iana.org/assignments/enterprise-numbers.

8.  Author's Address

  Kurt D. Zeilenga
  OpenLDAP Foundation

  EMail: [email protected]





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9.  Full Copyright Statement

  Copyright (C) The Internet Society (2003).  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 assignees.

  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.

Acknowledgement

  Funding for the RFC Editor function is currently provided by the
  Internet Society.



















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