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.
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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].
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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.
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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
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RFC 4526 LDAP Absolute True and False Filters June 2006
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