Internet Engineering Task Force (IETF)                       K. Zeilenga
Request for Comments: 6171                                 Isode Limited
Category: Standards Track                                     March 2011
ISSN: 2070-1721


The Lightweight Directory Access Protocol (LDAP) Don't Use Copy Control

Abstract

   This document defines the Lightweight Directory Access Protocol
   (LDAP) Don't Use Copy control extension, which allows a client to
   specify that copied information should not be used in providing
   service.  This control is based upon the X.511 dontUseCopy service
   control option.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6171.

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1.  Background and Intended Usage

   This document defines the Lightweight Directory Access Protocol
   (LDAP) [RFC4510] Don't Use Copy control extension.  The control may
   be attached to request messages to indicate that copied (replicated
   or cached) information [X.500] is not be used in providing service.
   This control is based upon the X.511 [X.511] dontUseCopy service
   control option.

   The Don't Use Copy control is intended to be used where the client
   requires the service be provided using original (master) information
   [X.500].  In absence of this control, the server is free to make use
   of copied (i.e., non-authoritative) information in providing the
   requested service.

   For instance, a client might desire to have an authoritative answer
   to a question of whether or not a particular user is a member of a
   group.  To ask this question of a server, the client might issue a
   compare request [RFC4511], with the Don't Use Copy control, where the
   entry parameter is the Distinguished Name (DN) of the group, the
   ava.attributeDesc is 'member', and the ava.assertionValue is the DN
   of the user in question.  If the server has access to the original
   (master) information directly or through chaining, it performs the
   operation against the original (master) information and returns
   compareTrue or compareFalse (or an error).  If the server does not
   have access to the original information, the server is obligated to
   either return a referral or an error.

   It is not intended that this control be used generally (e.g., for all
   LDAP interrogation operations) but only as required to ensure proper
   directory application behavior.  In general, directory applications
   ought to designed to use copied information well.

2.  Terminology

   DSA stands for Directory System Agent (or server).
   DSE stands for DSA-Specific Entry.

   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 RFC 2119 [RFC2119].

3.  The Don't Use Copy Control

   The Don't Use Copy control is an LDAP Control [RFC4511] whose
   controlType is 1.3.6.1.1.22 and controlValue is absent.  The
   criticality MUST be TRUE.  There is no corresponding response
   control.

   The control is appropriate for LDAP interrogation operations,
   including Compare and Search operations [RFC4511].  It is
   inappropriate for all other operations, including Abandon, Bind,
   Delete, Modify, ModifyDN, StartTLS, and Unbind operations [RFC4511].

   When the control is attached to an LDAP request, the requested
   operation MUST NOT be performed on copied information.  That is, the
   requested operation MUST be performed on original information.

   If original (master) information for the target or base object of the
   operation is not available (either locally or through chaining), the
   server MUST either return a referral directing the client to a server
   believed to be better able to service the request or return an
   appropriate result code (e.g., unwillingToPerform).

   It is noted that a referral, if returned, is not necessarily to the
   server holding the original (master) information.  It is also noted
   that an authoritative answer to the question might not be available
   to the client for any number of reasons.

   Where the client chases a referral to a server (as referenced by an
   LDAP URL) in the server response in order to obtain an authoritative
   response, the client MUST provide the dontUseCopy control with the
   interrogation request it makes to the referred to server.  While LDAP
   allows return of other kinds of URIs, the syntax and semantics of
   other kinds of URIs are left to future specifications.  The
    particulars of how to act upon other kinds of URIs are also left to
   future specifications.

   Servers implementing this technical specification SHOULD publish the
   object identifier 1.3.6.1.1.22 as a value of the 'supportedControl'
   attribute [RFC4512] in their root DSE.  A server MAY choose to
   advertise this extension only when the client is authorized to use
   it.

4.  Security Considerations

   This control is intended to be provided where providing service using
   copied information might lead to unexpected application behavior.

   Use of the Don't Use Copy control may permit an attacker to perform
   or amplify a denial-of-service attack by causing additional server
   resources to be employed, such as when the server chooses to chain
   the request instead of returning a referral.  Servers capable of such
   chaining can mitigate this threat by limiting chaining to a
   particular group of authenticated entities.

   LDAP is frequently used for storage and distribution of security-
   sensitive information, including access control and security policy
   information.  Failure to use the Don't Use Copy control may thus
   permit an attacker to gain unauthorized access by allowing reliance
   on stale data.

5.  IANA Considerations

5.1.  Object Identifier

   IANA has assigned an LDAP Object Identifier [RFC4520] to identify the
   LDAP Don't Use Copy Control defined in this document.

      Subject: Request for LDAP Object Identifier Registration
      Person & email address to contact for further information:
          Kurt Zeilenga <Kurt.Zeilenga@Isode.COM>
      Specification: RFC 6171
      Author/Change Controller: IESG
      Comments:
          Identifies the LDAP Don't Use Copy Control

5.2.  LDAP Protocol Mechanism

   IANA has registered this protocol mechanism [RFC4520] as follows.

      Subject: Request for LDAP Protocol Mechanism Registration
      Object Identifier: 1.3.6.1.1.22
      Description: Don't Use Copy Control
      Person & email address to contact for further information:
          Kurt Zeilenga <Kurt.Zeilenga@Isode.COM>
      Usage: Control
      Specification: RFC 6171
      Author/Change Controller: IESG
      Comments: none

6.  Acknowledgements

   The author thanks Ben Campbell, Phillip Hallam-Baker, and Ted Hardie
   for providing review and specific suggestions.

7.  References

7.1.  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., Ed., "Lightweight Directory Access Protocol
              (LDAP): Directory Information Models", RFC 4512, June
              2006.

7.2.  Informative References

   [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.511]    International Telecommunication Union - Telecommunication
              Standardization Sector, "The Directory: Abstract Service
              Definition", X.511(1993) (also ISO/IEC 9594-3:1993).

   [RFC4520]  Zeilenga, K., "Internet Assigned Numbers Authority (IANA)
              Considerations for the Lightweight Directory Access
              Protocol (LDAP)", BCP 64, RFC 4520, June 2006.

Author's Address

   Kurt D. Zeilenga
   Isode Limited

   EMail: Kurt.Zeilenga@Isode.COM