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rfc:rfc4526

Network Working Group K. Zeilenga Request for Comments: 4526 OpenLDAP Foundation Category: Standards Track June 2006

            Lightweight Directory Access Protocol (LDAP)
                  Absolute True and False Filters

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 (2006).

Abstract

 This document extends the Lightweight Directory Access Protocol
 (LDAP) to support absolute True and False filters based upon similar
 capabilities found in X.500 directory systems.  The document also
 extends the String Representation of LDAP Search Filters to support
 these filters.

Table of Contents

 1. Background ......................................................1
 2. Absolute True and False Filters .................................2
 3. Security Considerations .........................................2
 4. IANA Considerations .............................................3
 5. References ......................................................3
    5.1. Normative References .......................................3
    5.2. Informative References .....................................3

1. Background

 The X.500 Directory Access Protocol (DAP) [X.511] supports absolute
 True and False assertions.  An 'and' filter with zero elements always
 evaluates to True.  An 'or' filter with zero elements always
 evaluates to False.  These filters are commonly used when requesting
 DSA-specific Entries (DSEs) that do not necessarily have
 'objectClass' attributes; that is, where "(objectClass=*)" may
 evaluate to False.

Zeilenga Standards Track [Page 1] RFC 4526 LDAP Absolute True and False Filters June 2006

 Although LDAPv2 [RFC1777][RFC3494] placed no restriction on the
 number of elements in 'and' and 'or' filter sets, the LDAPv2 string
 representation [RFC1960][RFC3494] could not represent empty 'and' and
 'or' filter sets.  Due to this, absolute True or False filters were
 (unfortunately) eliminated from LDAPv3 [RFC4510].
 This documents extends LDAPv3 to support absolute True and False
 assertions by allowing empty 'and' and 'or' in Search filters
 [RFC4511] and extends the filter string representation [RFC4515] to
 allow empty filter lists.
 It is noted that certain search operations, such as those used to
 retrieve subschema information [RFC4512], require use of particular
 filters.  This document does not change these requirements.
 This feature is intended to allow a more direct mapping between DAP
 and LDAP (as needed to implement DAP-to-LDAP gateways).
 In this document, the key words "MUST", "MUST NOT", "REQUIRED",
 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
 and "OPTIONAL" are to be interpreted as described in BCP 14
 [RFC2119].

2. Absolute True and False Filters

 Implementations of this extension SHALL allow 'and' and 'or' choices
 with zero filter elements.
 An 'and' filter consisting of an empty set of filters SHALL evaluate
 to True.  This filter is represented by the string "(&)".
 An 'or' filter consisting of an empty set of filters SHALL evaluate
 to False.  This filter is represented by the string "(|)".
 Servers supporting this feature SHOULD publish the Object Identifier
 1.3.6.1.4.1.4203.1.5.3 as a value of the 'supportedFeatures'
 [RFC4512] attribute in the root DSE.
 Clients supporting this feature SHOULD NOT use the feature unless
 they know that the server supports it.

3. Security Considerations

 The (re)introduction of absolute True and False filters is not
 believed to raise any new security considerations.
 Implementors of this (or any) LDAPv3 extension should be familiar
 with general LDAPv3 security considerations [RFC4510].

Zeilenga Standards Track [Page 2] RFC 4526 LDAP Absolute True and False Filters June 2006

4. IANA Considerations

 Registration of this feature has been completed by the IANA
 [RFC4520].
 Subject: Request for LDAP Protocol Mechanism Registration Object
 Identifier: 1.3.6.1.4.1.4203.1.5.3 Description: True/False filters
 Person & email address to contact for further information:
      Kurt Zeilenga <kurt@openldap.org> Usage: Feature Specification:
 RFC 4526 Author/Change Controller: IESG Comments: none
 This OID was assigned [ASSIGN] by OpenLDAP Foundation, under its
 IANA-assigned private enterprise allocation [PRIVATE], for use in
 this specification.

5. References

5.1. Normative References

 [RFC2119]     Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC4510]     Zeilenga, K., Ed, "Lightweight Directory Access
               Protocol (LDAP): Technical Specification Road Map", RFC
               4510, June 2006.
 [RFC4511]     Sermersheim, J., Ed., "Lightweight Directory Access
               Protocol (LDAP): The Protocol", RFC 4511, June 2006.
 [RFC4512]     Zeilenga, K., "Lightweight Directory Access Protocol
               (LDAP): Directory Information Models", RFC 4512, June
               2006.
 [RFC4515]     Smith, M., Ed. and T. Howes, "Lightweight Directory
               Access Protocol (LDAP): String Representation of Search
               Filters", RFC 4515, June 2006.

5.2. Informative References

 [RFC1777]     Yeong, W., Howes, T., and S. Kille, "Lightweight
               Directory Access Protocol", RFC 1777, March 1995.
 [RFC1960]     Howes, T., "A String Representation of LDAP Search
               Filters", RFC 1960, June 1996.
 [RFC3494]     Zeilenga, K., "Lightweight Directory Access Protocol
               version 2 (LDAPv2) to Historic Status", RFC 3494, March
               2003.

Zeilenga Standards Track [Page 3] RFC 4526 LDAP Absolute True and False Filters June 2006

 [RFC4520]     Zeilenga, K., "Internet Assigned Numbers Authority
               (IANA) Considerations for the Lightweight Directory
               Access Protocol (LDAP)", BCP 64, RFC 4520, June 2006.
 [X.500]       International Telecommunication Union -
               Telecommunication Standardization Sector, "The
               Directory -- Overview of concepts, models and
               services," X.500(1993) (also ISO/IEC 9594-1:1994).
 [X.501]       International Telecommunication Union -
               Telecommunication Standardization Sector, "The
               Directory -- Models," X.501(1993) (also ISO/IEC 9594-
               2:1994).
 [X.511]       International Telecommunication Union -
               Telecommunication Standardization Sector, "The
               Directory: Abstract Service Definition", X.511(1993)
               (also ISO/IEC 9594-3:1993).
 [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.

Author's Address

 Kurt D. Zeilenga
 OpenLDAP Foundation
 EMail: Kurt@OpenLDAP.org

Zeilenga Standards Track [Page 4] RFC 4526 LDAP Absolute True and False Filters June 2006

Full Copyright Statement

 Copyright (C) The Internet Society (2006).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM 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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Acknowledgement

 Funding for the RFC Editor function is provided by the IETF
 Administrative Support Activity (IASA).

Zeilenga Standards Track [Page 5]

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