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rfc:rfc3674

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).

Zeilenga Standards Track [Page 1] RFC 3674 Feature Discovery in LDAP December 2003

 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.

Zeilenga Standards Track [Page 2] RFC 3674 Feature Discovery in LDAP December 2003

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 <kurt@OpenLDAP.org>
    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.

Zeilenga Standards Track [Page 3] RFC 3674 Feature Discovery in LDAP December 2003

 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: Kurt@OpenLDAP.org

Zeilenga Standards Track [Page 4] RFC 3674 Feature Discovery in LDAP December 2003

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.

Zeilenga Standards Track [Page 5]

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