|Title||Feature Discovery in Lightweight Directory Access Protocol (LDAP)
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 (C) The Internet Society (2003). All Rights Reserved.
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
Schema definitions are provided using LDAP description formats
[RFC2252]. Definitions provided here are formatted (line wrapped)
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
The 'supportedFeatures' attribute type is described as follows:
DESC 'features supported by the server'
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.
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: 18.104.22.168.4.1.422.214.171.124
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
This document is based upon input from the IETF LDAPEXT working
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
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standards-related documentation can be found in BCP-11. Copies of
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The IETF invites any interested party to bring to its attention any
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this standard. Please address the information to the IETF Executive
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,
[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
[ASSIGN] OpenLDAP Foundation, "OpenLDAP OID Delegations",
[PRIVATE] IANA, "Private Enterprise Numbers",
8. Author's Address
Kurt D. Zeilenga
9. Full Copyright Statement
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