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Network Working Group                                        K. ZeilengaRequest for Comments: 3674                           OpenLDAP FoundationCategory: Standards Track                                  December 2003Feature 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 inBCP 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 inBCP 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 20034.  IANA Considerations4.1.  Registration of Features as Protocol Mechanisms   Future specifications detailing LDAP features are to register each   feature as a LDAP Protocol Mechanism per guidance given inBCP 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 inBCP-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.  References7.1.  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",RFC3673, 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.orgZeilenga                    Standards Track                     [Page 4]

RFC 3674               Feature Discovery in LDAP           December 20039.  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]