Independent Submission                                       K. Zeilenga
Request for Comments: 5805                                 Isode Limited
Category: Experimental                                        March 2010
ISSN: 2070-1721


       Lightweight Directory Access Protocol (LDAP) Transactions

Abstract

   Lightweight Directory Access Protocol (LDAP) update operations, such
   as Add, Delete, and Modify operations, have atomic, consistency,
   isolation, durability (ACID) properties.  Each of these update
   operations act upon an entry.  It is often desirable to update two or
   more entries in a single unit of interaction, a transaction.
   Transactions are necessary to support a number of applications
   including resource provisioning.  This document extends LDAP to
   support transactions.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  This is a contribution to the RFC Series, independently
   of any other RFC stream.  The RFC Editor has chosen to publish this
   document at its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not a candidate for any level of Internet
   Standard; see 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/rfc5805.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.



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1.  Overview

   This document extends the Lightweight Directory Access Protocol
   (LDAP) [RFC4510] to allow clients to relate a number of update
   operations [RFC4511] and have them performed as one unit of
   interaction, a transaction.  As with distinct update operations, each
   transaction has atomic, consistency, isolation, and durability (ACID)
   properties [ACID].

   This extension consists of two extended operations, one control, and
   one unsolicited notification message.  The Start Transaction
   operation is used to obtain a transaction identifier.  This
   identifier is then attached to multiple update operations to indicate
   that they belong to the transaction using the Transaction
   Specification control.  The End Transaction is used to settle (commit
   or abort) the transaction.  The Aborted Transaction Notice is
   provided by the server to notify the client that the server is no
   longer willing or able to process an outstanding transaction.

1.1.  Conventions and Terminology

   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].

   Protocol elements are described using ASN.1 [X.680] with implicit
   tags.  The term "BER-encoded" means the element is to be encoded
   using the Basic Encoding Rules [X.690] under the restrictions
   detailed in Section 5.1 of [RFC4511].

   DSA stands for "Directory System Agent" (a server).  DSE stands for
   "DSA-specific entry".

2.  Elements of an LDAP Transaction

2.1.  Start Transaction Request and Response

   A Start Transaction Request is an LDAPMessage of CHOICE extendedReq
   where the requestName is 1.3.6.1.1.21.1 and the requestValue is
   absent.

   A Start Transaction Response is an LDAPMessage of CHOICE extendedRes
   sent in response to a Start Transaction Request.  Its responseName is
   absent.  When the resultCode is success (0), responseValue is present
   and contains a transaction identifier.  Otherwise, the responseValue
   is absent.





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2.2.  Transaction Specification Control

   A Transaction Specification Control is an LDAPControl where the
   controlType is 1.3.6.1.1.21.2, the criticality is TRUE, and the
   controlValue is a transaction identifier.  The control is appropriate
   for update requests including Add, Delete, Modify, and ModifyDN
   (Rename) requests [RFC4511], as well as the Password Modify requests
   [RFC3062].

   As discussed in Section 4, the Transaction Specification control can
   be used in conjunction with request controls appropriate for the
   update request.

2.3.  End Transactions Request and Response

   An End Transaction Request is an LDAPMessage of CHOICE extendedReq
   where the requestName is 1.3.6.1.1.21.3 and the requestValue is
   present and contains a BER-encoded txnEndReq.

      txnEndReq ::= SEQUENCE {
           commit         BOOLEAN DEFAULT TRUE,
           identifier     OCTET STRING }

   A commit value of TRUE indicates a request to commit the transaction
   identified by the identifier.  A commit value of FALSE indicates a
   request to abort the identified transaction.

   An End Transaction Response is an LDAPMessage sent in response to a
   End Transaction Request.  Its response name is absent.  The
   responseValue when present contains a BER-encoded txnEndRes.

      txnEndRes ::= SEQUENCE {
           messageID MessageID OPTIONAL,
                -- msgid associated with non-success resultCode
           updatesControls SEQUENCE OF updateControls SEQUENCE {
                messageID MessageID,
                     -- msgid associated with controls
                controls  Controls
           } OPTIONAL
      }
      -- where MessageID and Controls are as specified in RFC 4511

   The txnEndRes.messageID provides the message id of the update request
   associated with a non-success response.  txnEndRes.messageID is
   absent when resultCode of the End Transaction Response is success
   (0).





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   The txnEndRes.updatesControls provides a facility for returning
   response controls that normally (i.e., in the absence of
   transactions) would be returned in an update response.  The
   updateControls.messageID provides the message id of the update
   request associated with the response controls provided in
   updateControls.controls.

   The txnEndRes.updatesControls is absent when there are no update
   response controls to return.

   If both txnEndRes.messageID and txnEndRes.updatesControl are absent,
   the responseValue of the End Transaction Response is absent.

2.4.  Aborted Transaction Notice

   The Aborted Transaction Notice is an Unsolicited Notification message
   where the responseName is 1.3.6.1.1.21.4 and responseValue is present
   and contains a transaction identifier.

3.  An LDAP Transaction

3.1.  Extension Discovery

   To allow clients to discover support for this extension, servers
   implementing this specification SHOULD publish 1.3.6.1.1.21.1 and
   1.3.6.1.1.21.3 as values of the 'supportedExtension' attribute
   [RFC4512] within the Root DSE, and publish the 1.3.6.1.1.21.2 as a
   value of the 'supportedControl' attribute [RFC4512] of the Root DSE.

   A server MAY choose to advertise this extension only when the client
   is authorized to use it.

3.2.  Starting a Transaction

   A client wishing to perform a sequence of directory updates as a
   transaction issues a Start Transaction Request.  A server that is
   willing and able to support transactions responds to this request
   with a Start Transaction Response providing a transaction identifier
   and with a resultCode of success (0).  Otherwise, the server responds
   with a Start Transaction Response with a resultCode other than
   success indicating the nature of the failure.

   The transaction identifier provided upon successful start of a
   transaction is used in subsequent protocol messages to identify this
   transaction.






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3.3.  Specification of a Transaction

   The client then can issue one or more update requests, each with a
   Transaction Specification control containing the transaction
   identifier indicating the updates are to be processed as part of the
   transaction.  Each of these update requests MUST have a different
   MessageID value.  If the server is unwilling or unable to attempt to
   process the requested update operation as part of the transaction,
   the server immediately returns the appropriate response to the
   request with a resultCode indicating the nature of the failure.
   Otherwise, the server immediately returns a resultCode of success (0)
   and the defers further processing of the operation is then deferred
   until settlement.

   If the server becomes unwilling or unable to continue the
   specification of a transaction, the server issues an Aborted
   Transaction Notice with a non-success resultCode indicating the
   nature of the failure.  All operations that were to be processed as
   part of the transaction are implicitly abandoned.  Upon receipt of an
   Aborted Transaction Notice, the client is to discontinue all use of
   the transaction identifier as the transaction is null and void.  Any
   future use of identifier by the client will result in a response
   containing a non-success resultCode.

3.4.  Transaction Settlement

   A client requests settlement of transaction by issuing an End
   Transaction Request for the transaction indicating whether it desires
   the transaction to be committed or aborted.

   Upon receipt of a request to abort the transaction, the server is to
   abort the identified transaction (abandoning all operations that are
   part of the transaction) and indicate that it has done so by
   returning an End Transaction Response with a resultCode of success
   (0).

   Upon receipt of a request to commit the transaction, the server
   processes all update operations of the transaction as one atomic,
   durable, isolated, and consistent action with each requested update
   being processed in turn.  Either all of the requested updates are to
   be successfully applied or none of the requested are to be applied.
   The server returns an End Transaction Response with a resultCode of
   success (0) and no responseValue to indicate all the requested
   updates were applied.  Otherwise, the server returns an End
   Transaction Response with a non-success resultCode indicating the
   nature of the failure.  If the failure is associated with a





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   particular update request, the txnEndRes.messageID in the
   responseValue is the message id of this update request.  If the
   failure was not associated with any particular update request, no
   txnEnd.messageID is provided.

   There is no requirement that a server serialize transactions or
   updates requested outside of a transaction.  That is, a server MAY
   process multiple commit requests (from one or more clients) acting
   upon different sets of entries concurrently.  A server MUST avoid
   deadlock.

3.5.  Miscellaneous Issues

   Transactions cannot be nested.

   Each LDAP transaction should be initiated, specified, and settled
   within a stable security context.  Between the Start Request and the
   End Response, the peers SHOULD avoid negotiating new security
   associations and/or layers.

   Upon receipt of a Bind or Unbind request, the server SHALL abort any
   and all outstanding transactions without notice and nullify their
   identifiers.

4.  Interaction with Other Extensions

   The LDAP Transaction extension may be used with many but not all LDAP
   control extensions designed to extend update (and possibly other)
   operations.  The subsections that follow discuss interaction with a
   number of control extensions.  Interaction with other control
   extensions may be discussed in other documents, in particular in
   control extension specifications.

4.1.  Assertion Control

   The Assertion [RFC4528] control is appropriate for use with update
   requests specified as part of a transaction.  The evaluation of the
   assertion is performed as part of the transaction.

   The Assertion control is inappropriate for use with either the Start
   or End Transaction Extended operations.

4.2.  ManageDsaIT Control

   The ManageDsaIT [RFC3296] control is appropriate for use with update
   requests specified as part of a transaction.





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   The ManageDsaIT control is inappropriate for use with either the
   Start or End Transaction Extended operations.

4.4.  Proxied Authorization Control

   The Proxied Authorization [RFC4370] control is appropriate for use
   with the Start Transaction Extended operation, but not the End
   Transaction Extended operation or any update request specified as
   part of a transaction.

   To request that a transaction be performed under a different
   authorization, the client provides a Proxied Authorization control
   with the Transaction Start Request.  If the client is not authorized
   to assume the requested authorization identity, the server is to
   return the authorizationDenied (123) resultCode in its response.
   Otherwise, further processing of the request and transaction is
   performed under the requested authorization identity.

   Any proxied authorization request attached to an update request
   specified as part of a transaction, or attached to a Transaction End
   Request, is to be regarded as a protocol error.

4.5.  Read Entry Controls

   The Pre- and Post-Read Entry [RFC4527] request control are
   appropriate for use with update requests specified as part of a
   transaction.

   The response control produced in response to a Pre- or Post-Read
   Entry request control is returned in the txnEndRes.updatesControls
   field of responseValue of the End Transaction Response.

   The Pre- and Post-Read Entry controls are inappropriate for use in
   the LDAPMessage.controls field of the Transaction Start and End
   Request and Response messages.

5.  Distributed Directory Considerations

   The LDAP/X.500 models provide for distributed directory operations,
   including server-side chaining and client-side chasing of referrals.

   This document does not preclude servers from chaining operations that
   are part of a transaction.  However, if a server does attempt such
   chaining, it MUST ensure that transaction semantics are provided.

   The mechanism defined by this document does not support client-side
   chasing.  Transaction identifiers are specific to a particular LDAP
   association (as established via the LDAP Bind operation).



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   The LDAP/X.500 models provide for a single-master/multiple-shadow
   replication architecture.  There is no requirement that changes made
   to the directory based upon processing a transaction be replicated as
   one atomic action.  Hence, clients SHOULD NOT assume tight data
   consistency nor fast data convergence of shadow copies unless they
   have prior knowledge that these properties are provided.  Note that
   DontUseCopy control [DONTUSECOPY] may be used in conjunction with the
   LDAP search request to ask for the return of the authoritative copy
   of the entry.

6.  Security Considerations

   Transaction mechanisms may be the target of denial-of-service
   attacks, especially where implementations lock shared resources for
   the duration of a transaction.

   General security considerations [RFC4510], especially those
   associated with update operations [RFC4511], apply to this extension.

7.  IANA Considerations

   The Internet Assigned Numbers Authority (IANA) has made the following
   assignments.

7.1.  Object Identifier

   IANA has assigned an LDAP Object Identifier (21) [RFC4520] to
   identify the protocol elements specified 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 5805
      Author/Change Controller: Kurt Zeilenga <Kurt.Zeilenga@Isode.COM>
      Comments: Identifies protocol elements for LDAP Transactions
















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7.2.  LDAP Protocol Mechanism

   IANA has registered the protocol mechanisms [RFC4520] specified in
   this document.

      Subject: Request for LDAP Protocol Mechanism Registration
      Object Identifier: see table
      Description: see table
      Person & email address to contact for further information:
          Kurt Zeilenga <Kurt.Zeilenga@Isode.COM>
      Specification: RFC 5805
      Author/Change Controller: Kurt Zeilenga <Kurt.Zeilenga@Isode.COM>
      Comments:

      Object Identifier   Type  Description
      ------------------- ----  ----------------------------------
      1.3.6.1.1.21.1      E     Start Transaction Extended Request
      1.3.6.1.1.21.2      C     Transaction Specification Control
      1.3.6.1.1.21.3      E     End Transaction Extended Request
      1.3.6.1.1.21.4      N     Aborted Transaction Notice

      Legend
      ------------------------
      C => supportedControl
      E => supportedExtension
      N => Unsolicited Notice

8.  Acknowledgments

   The author gratefully acknowledges the contributions made by Internet
   Engineering Task Force participants.

9.  References

9.1.  Normative References

   [RFC2119]     Bradner, S., "Key words for use in RFCs to Indicate
                 Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3062]     Zeilenga, K., "LDAP Password Modify Extended
                 Operation", RFC 3062, February 2001.

   [RFC3296]     Zeilenga, K., "Named Subordinate References in
                 Lightweight Directory Access Protocol (LDAP)
                 Directories", RFC 3296, July 2002.






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   [RFC4370]     Weltman, R., "Lightweight Directory Access Protocol
                 (LDAP) Proxied Authorization Control", RFC 4370,
                 February 2006.

   [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.

   [RFC4527]     Zeilenga, K., "Lightweight Directory Access Protocol
                 (LDAP) Read Entry Controls", RFC 4527, June 2006.

   [RFC4528]     Zeilenga, K., "Lightweight Directory Access Protocol
                 (LDAP) Assertion Control", RFC 4528, June 2006.

   [X.680]       International Telecommunication Union -
                 Telecommunication Standardization Sector, "Abstract
                 Syntax Notation One (ASN.1) - Specification of Basic
                 Notation", X.680(2002) (also ISO/IEC 8824-1:2002).

   [X.690]       International Telecommunication Union -
                 Telecommunication Standardization Sector,
                 "Specification of ASN.1 encoding rules: Basic Encoding
                 Rules (BER), Canonical Encoding Rules (CER), and
                 Distinguished Encoding Rules (DER)", X.690(2002) (also
                 ISO/IEC 8825-1:2002).

9.2.  Informative References

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

   [ACID]        "Information technology -- Open Systems Interconnection
                 -- Distributed Transaction Processing -- Part 1: OSI TP
                 Model", Section 4, ISO/IEC 10026-1:1992.

   [DONTUSECOPY] Zeilenga, K., "The LDAP Don't Use Copy Control", Work
                 in Progress, December 2009.






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Author's Address

   Kurt D. Zeilenga
   Isode Limited

   EMail: Kurt.Zeilenga@Isode.COM













































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