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.

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.

Although LDAPv2 RFC1777RFC3494 placed no restriction on the number of elements in 'and' and 'or' filter sets, the LDAPv2 string representation RFC1960RFC3494 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.

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.

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.

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 <[email protected]> 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.

References

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.

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.

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: [email protected]

Full Copyright Statement

Copyright (C) The Internet Society (2006).

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