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+Network Working Group                                        K. Zeilenga
+Request for Comments: 4533                           OpenLDAP Foundation
+Category: Experimental                                         J.H. Choi
+                                                         IBM Corporation
+                                                               June 2006
+
+
+           The Lightweight Directory Access Protocol (LDAP)
+                   Content Synchronization Operation
+
+Status of This Memo
+
+   This memo defines an Experimental Protocol for the Internet
+   community.  It does not specify an Internet standard of any kind.
+   Discussion and suggestions for improvement are requested.
+   Distribution of this memo is unlimited.
+
+Copyright Notice
+
+   Copyright (C) The Internet Society (2006).
+
+IESG Note
+
+   The IESG notes that this work was originally discussed in the LDUP
+   working group.  The group came to consensus on a different approach,
+   documented in RFC 3928; that document is on the standards track and
+   should be reviewed by those considering implementation of this
+   proposal.
+
+Abstract
+
+   This specification describes the Lightweight Directory Access
+   Protocol (LDAP) Content Synchronization Operation.  The operation
+   allows a client to maintain a copy of a fragment of the Directory
+   Information Tree (DIT).  It supports both polling for changes and
+   listening for changes.  The operation is defined as an extension of
+   the LDAP Search Operation.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Zeilenga & Choi               Experimental                      [Page 1]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+Table of Contents
+
+   1. Introduction ....................................................3
+      1.1. Background .................................................3
+      1.2. Intended Usage .............................................4
+      1.3. Overview ...................................................5
+      1.4. Conventions ................................................8
+   2. Elements of the Sync Operation ..................................8
+      2.1. Common ASN.1 Elements ......................................9
+      2.2. Sync Request Control .......................................9
+      2.3. Sync State Control ........................................10
+      2.4. Sync Done Control .........................................10
+      2.5. Sync Info Message .........................................11
+      2.6. Sync Result Codes .........................................11
+   3. Content Synchronization ........................................11
+      3.1. Synchronization Session ...................................12
+      3.2. Content Determination .....................................12
+      3.3. refreshOnly Mode ..........................................13
+      3.4. refreshAndPersist Mode ....................................16
+      3.5. Search Request Parameters .................................17
+      3.6. objectName ................................................18
+      3.7. Canceling the Sync Operation ..............................19
+      3.8. Refresh Required ..........................................19
+      3.9. Chattiness Considerations .................................20
+      3.10. Operation Multiplexing ...................................21
+   4. Meta Information Considerations ................................22
+      4.1. Entry DN ..................................................22
+      4.2. Operational Attributes ....................................22
+      4.3. Collective Attributes .....................................23
+      4.4. Access and Other Administrative Controls ..................23
+   5. Interaction with Other Controls ................................23
+      5.1. ManageDsaIT Control .......................................24
+      5.2. Subentries Control ........................................24
+   6. Shadowing Considerations .......................................24
+   7. Security Considerations ........................................25
+   8. IANA Considerations ............................................26
+      8.1. Object Identifier .........................................26
+      8.2. LDAP Protocol Mechanism ...................................26
+      8.3. LDAP Result Codes .........................................26
+   9. Acknowledgements ...............................................26
+   10. Normative References ..........................................27
+   11. Informative References ........................................28
+   Appendix A.  CSN-based Implementation Considerations ..............29
+
+
+
+
+
+
+
+
+Zeilenga & Choi               Experimental                      [Page 2]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+1.  Introduction
+
+   The Lightweight Directory Access Protocol (LDAP) [RFC4510] provides a
+   mechanism, the search operation [RFC4511], that allows a client to
+   request directory content matching a complex set of assertions and to
+   request that the server return this content, subject to access
+   control and other restrictions, to the client.  However, LDAP does
+   not provide (despite the introduction of numerous extensions in this
+   area) an effective and efficient mechanism for maintaining
+   synchronized copies of directory content.  This document introduces a
+   new mechanism specifically designed to meet the content
+   synchronization requirements of sophisticated directory applications.
+
+   This document defines the LDAP Content Synchronization Operation, or
+   Sync Operation for short, which allows a client to maintain a
+   synchronized copy of a fragment of a Directory Information Tree
+   (DIT).  The Sync Operation is defined as a set of controls and other
+   protocol elements that extend the Search Operation.
+
+1.1.  Background
+
+   Over the years, a number of content synchronization approaches have
+   been suggested for use in LDAP directory services.  These approaches
+   are inadequate for one or more of the following reasons:
+
+      -  failure to ensure a reasonable level of convergence;
+
+      -  failure to detect that convergence cannot be achieved (without
+         reload);
+
+      -  require pre-arranged synchronization agreements;
+
+      -  require the server to maintain histories of past changes to DIT
+         content and/or meta information;
+
+      -  require the server to maintain synchronization state on a per-
+         client basis; and/or
+
+      -  are overly chatty.
+
+   The Sync Operation provides eventual convergence of synchronized
+   content when possible and, when not, notification that a full reload
+   is required.
+
+   The Sync Operation does not require pre-arranged synchronization
+   agreements.
+
+
+
+
+
+Zeilenga & Choi               Experimental                      [Page 3]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+   The Sync Operation does not require that servers maintain or use any
+   history of past changes to the DIT or to meta information.  However,
+   servers may maintain and use histories (e.g., change logs,
+   tombstones, DIT snapshots) to reduce the number of messages generated
+   and to reduce their size.  As it is not always feasible to maintain
+   and use histories, the operation may be implemented using purely
+   (current) state-based approaches.  The Sync Operation allows use of
+   either the state-based approach or the history-based approach on an
+   operation-by-operation basis to balance the size of history and the
+   amount of traffic.  The Sync Operation also allows the combined use
+   of the state-based and the history-based approaches.
+
+   The Sync Operation does not require that servers maintain
+   synchronization state on a per-client basis.  However, servers may
+   maintain and use per-client state information to reduce the number of
+   messages generated and the size of such messages.
+
+   A synchronization mechanism can be considered overly chatty when
+   synchronization traffic is not reasonably bounded.  The Sync
+   Operation traffic is bounded by the size of updated (or new) entries
+   and the number of unchanged entries in the content.  The operation is
+   designed to avoid full content exchanges, even when the history
+   information available to the server is insufficient to determine the
+   client's state.  The operation is also designed to avoid transmission
+   of out-of-content history information, as its size is not bounded by
+   the content and it is not always feasible to transmit such history
+   information due to security reasons.
+
+   This document includes a number of non-normative appendices providing
+   additional information to server implementors.
+
+1.2.  Intended Usage
+
+   The Sync Operation is intended to be used in applications requiring
+   eventually-convergent content synchronization.  Upon completion of
+   each synchronization stage of the operation, all information to
+   construct a synchronized client copy of the content has been provided
+   to the client or the client has been notified that a complete content
+   reload is necessary.  Except for transient inconsistencies due to
+   concurrent operation (or other) processing at the server, the client
+   copy is an accurate reflection of the content held by the server.
+   Transient inconsistencies will be resolved by subsequent
+   synchronization operations.
+
+
+
+
+
+
+
+
+Zeilenga & Choi               Experimental                      [Page 4]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+   Possible uses include the following:
+
+      -  White page service applications may use the Sync Operation to
+         maintain a current copy of a DIT fragment, for example, a mail
+         user agent that uses the sync operation to maintain a local
+         copy of an enterprise address book.
+
+      -  Meta-information engines may use the Sync Operation to maintain
+         a copy of a DIT fragment.
+
+      -  Caching proxy services may use the Sync Operation to maintain a
+         coherent content cache.
+
+      -  Lightweight master-slave replication between heterogeneous
+         directory servers.  For example, the Sync Operation can be used
+         by a slave server to maintain a shadow copy of a DIT fragment.
+         (Note: The International Telephone Union (ITU) has defined the
+         X.500 Directory [X.500] Information Shadowing Protocol (DISP)
+         [X.525], which may be used for master-slave replication between
+         directory servers.  Other experimental LDAP replication
+         protocols also exist.)
+
+   This protocol is not intended to be used in applications requiring
+   transactional data consistency.
+
+   As this protocol transfers all visible values of entries belonging to
+   the content upon change instead of change deltas, this protocol is
+   not appropriate for bandwidth-challenged applications or deployments.
+
+1.3.  Overview
+
+   This section provides an overview of basic ways the Sync Operation
+   can be used to maintain a synchronized client copy of a DIT fragment.
+
+      -  Polling for changes: refreshOnly mode
+
+      -  Listening for changes: refreshAndPersist mode
+
+1.3.1.  Polling for Changes (refreshOnly)
+
+   To obtain its initial client copy, the client issues a Sync request:
+   a search request with the Sync Request Control with mode set to
+   refreshOnly.  The server, much like it would with a normal search
+   operation, returns (subject to access controls and other
+   restrictions) the content matching the search criteria (baseObject,
+   scope, filter, attributes).  Additionally, with each entry returned,
+   the server provides a Sync State Control indicating state add.  This
+   control contains the Universally Unique Identifier (UUID) [UUID] of
+
+
+
+Zeilenga & Choi               Experimental                      [Page 5]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+   the entry [RFC4530].  Unlike the Distinguished Name (DN), which may
+   change over time, an entry's UUID is stable.  The initial content is
+   followed by a SearchResultDone with a Sync Done Control.  The Sync
+   Done Control provides a syncCookie.  The syncCookie represents
+   session state.
+
+   To poll for updates to the client copy, the client reissues the Sync
+   Operation with the syncCookie previously returned.  The server, much
+   as it would with a normal search operation, determines which content
+   would be returned as if the operation were a normal search operation.
+   However, using the syncCookie as an indicator of what content the
+   client was sent previously, the server sends copies of entries that
+   have changed with a Sync State Control indicating state add.  For
+   each changed entry, all (modified or unmodified) attributes belonging
+   to the content are sent.
+
+   The server may perform either or both of the two distinct
+   synchronization phases that are distinguished by how to synchronize
+   entries deleted from the content: the present and the delete phases.
+   When the server uses a single phase for the refresh stage, each phase
+   is marked as ended by a SearchResultDone with a Sync Done Control.  A
+   present phase is identified by a FALSE refreshDeletes value in the
+   Sync Done Control.  A delete phase is identified by a TRUE
+   refreshDeletes value.  The present phase may be followed by a delete
+   phase.  The two phases are delimited by a refreshPresent Sync Info
+   Message having a FALSE refreshDone value.  In the case that both the
+   phases are used, the present phase is used to bring the client copy
+   up to the state at which the subsequent delete phase can begin.
+
+   In the present phase, the server sends an empty entry (i.e., no
+   attributes) with a Sync State Control indicating state present for
+   each unchanged entry.
+
+   The delete phase may be used when the server can reliably determine
+   which entries in the prior client copy are no longer present in the
+   content and the number of such entries is less than or equal to the
+   number of unchanged entries.  In the delete mode, the server sends an
+   empty entry with a Sync State Control indicating state delete for
+   each entry that is no longer in the content, instead of returning an
+   empty entry with state present for each present entry.
+
+   The server may send syncIdSet Sync Info Messages containing the set
+   of UUIDs of either unchanged present entries or deleted entries,
+   instead of sending multiple individual messages.  If refreshDeletes
+   of syncIdSet is set to FALSE, the UUIDs of unchanged present entries
+   are contained in the syncUUIDs set; if refreshDeletes of syncIdSet is
+   set to TRUE, the UUIDs of the entries no longer present in the
+   content are contained in the syncUUIDs set.  An optional cookie can
+
+
+
+Zeilenga & Choi               Experimental                      [Page 6]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+   be included in the syncIdSet to represent the state of the content
+   after synchronizing the presence or the absence of the entries
+   contained in the syncUUIDs set.
+
+   The synchronized copy of the DIT fragment is constructed by the
+   client.
+
+   If refreshDeletes of syncDoneValue is FALSE, the new copy includes
+   all changed entries returned by the reissued Sync Operation, as well
+   as all unchanged entries identified as being present by the reissued
+   Sync Operation, but whose content is provided by the previous Sync
+   Operation.  The unchanged entries not identified as being present are
+   deleted from the client content.  They had been either deleted,
+   moved, or otherwise scoped-out from the content.
+
+   If refreshDeletes of syncDoneValue is TRUE, the new copy includes all
+   changed entries returned by the reissued Sync Operation, as well as
+   all other entries of the previous copy except for those that are
+   identified as having been deleted from the content.
+
+   The client can, at some later time, re-poll for changes to this
+   synchronized client copy.
+
+1.3.2.  Listening for Changes (refreshAndPersist)
+
+   Polling for changes can be expensive in terms of server, client, and
+   network resources.  The refreshAndPersist mode allows for active
+   updates of changed entries in the content.
+
+   By selecting the refreshAndPersist mode, the client requests that the
+   server send updates of entries that are changed after the initial
+   refresh content is determined.  Instead of sending a SearchResultDone
+   Message as in polling, the server sends a Sync Info Message to the
+   client indicating that the refresh stage is complete and then enters
+   the persist stage.  After receipt of this Sync Info Message, the
+   client will construct a synchronized copy as described in Section
+   1.3.1.
+
+   The server may then send change notifications as the result of the
+   original Sync search request, which now remains persistent in the
+   server.  For entries to be added to the returned content, the server
+   sends a SearchResultEntry (with attributes) with a Sync State Control
+   indicating state add.  For entries to be deleted from the content,
+   the server sends a SearchResultEntry containing no attributes and a
+   Sync State Control indicating state delete.  For entries to be
+   modified in the return content, the server sends a SearchResultEntry
+   (with attributes) with a Sync State Control indicating state modify.
+
+
+
+
+Zeilenga & Choi               Experimental                      [Page 7]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+   Upon modification of an entry, all (modified or unmodified)
+   attributes belonging to the content are sent.
+
+   Note that renaming an entry of the DIT may cause an add state change
+   where the entry is renamed into the content, a delete state change
+   where the entry is renamed out of the content, and a modify state
+   change where the entry remains in the content.  Also note that a
+   modification of an entry of the DIT may cause an add, delete, or
+   modify state change to the content.
+
+   Upon receipt of a change notification, the client updates its copy of
+   the content.
+
+   If the server desires to update the syncCookie during the persist
+   stage, it may include the syncCookie in any Sync State Control or
+   Sync Info Message returned.
+
+   The operation persists until canceled [RFC3909] by the client or
+   terminated by the server.  A Sync Done Control shall be attached to
+   SearchResultDone Message to provide a new syncCookie.
+
+1.4.  Conventions
+
+   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].
+
+   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].
+
+2.  Elements of the Sync Operation
+
+   The Sync Operation is defined as an extension to the LDAP Search
+   Operation [RFC4511] where the directory user agent (DUA or client)
+   submits a SearchRequest Message with a Sync Request Control and the
+   directory system agent (DSA or server) responds with zero or more
+   SearchResultEntry Messages, each with a Sync State Control; zero or
+   more SearchResultReference Messages, each with a Sync State Control;
+   zero or more Sync Info Intermediate Response Messages; and a
+   SearchResultDone Message with a Sync Done Control.
+
+   To allow clients to discover support for this operation, servers
+   implementing this operation SHOULD publish 1.3.6.1.4.1.4203.1.9.1.1
+   as a value of the 'supportedControl' attribute [RFC4512] of the root
+   DSA-specific entry (DSE).  A server MAY choose to advertise this
+   extension only when the client is authorized to use it.
+
+
+
+Zeilenga & Choi               Experimental                      [Page 8]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+2.1.  Common ASN.1 Elements
+
+2.1.1.  syncUUID
+
+   The syncUUID data type is an OCTET STRING holding a 128-bit
+   (16-octet) Universally Unique Identifier (UUID) [UUID].
+
+      syncUUID ::= OCTET STRING (SIZE(16))
+           -- constrained to UUID
+
+2.1.2.  syncCookie
+
+   The syncCookie is a notational convenience to indicate that, while
+   the syncCookie type is encoded as an OCTET STRING, its value is an
+   opaque value containing information about the synchronization session
+   and its state.  Generally, the session information would include a
+   hash of the operation parameters that the server requires not be
+   changed and the synchronization state information would include a
+   commit (log) sequence number, a change sequence number, or a time
+   stamp.  For convenience of description, the term "no cookie" refers
+   either to a null cookie or to a cookie with pre-initialized
+   synchronization state.
+
+      syncCookie ::= OCTET STRING
+
+2.2.  Sync Request Control
+
+   The Sync Request Control is an LDAP Control [RFC4511] where the
+   controlType is the object identifier 1.3.6.1.4.1.4203.1.9.1.1 and the
+   controlValue, an OCTET STRING, contains a BER-encoded
+   syncRequestValue.  The criticality field is either TRUE or FALSE.
+
+      syncRequestValue ::= SEQUENCE {
+          mode ENUMERATED {
+              -- 0 unused
+              refreshOnly       (1),
+              -- 2 reserved
+              refreshAndPersist (3)
+          },
+          cookie     syncCookie OPTIONAL,
+          reloadHint BOOLEAN DEFAULT FALSE
+      }
+
+   The Sync Request Control is only applicable to the SearchRequest
+   Message.
+
+
+
+
+
+
+Zeilenga & Choi               Experimental                      [Page 9]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+2.3.  Sync State Control
+
+   The Sync State Control is an LDAP Control [RFC4511] where the
+   controlType is the object identifier 1.3.6.1.4.1.4203.1.9.1.2 and the
+   controlValue, an OCTET STRING, contains a BER-encoded syncStateValue.
+   The criticality is FALSE.
+
+      syncStateValue ::= SEQUENCE {
+          state ENUMERATED {
+              present (0),
+              add (1),
+              modify (2),
+              delete (3)
+          },
+          entryUUID syncUUID,
+          cookie    syncCookie OPTIONAL
+      }
+
+   The Sync State Control is only applicable to SearchResultEntry and
+   SearchResultReference Messages.
+
+2.4.  Sync Done Control
+
+   The Sync Done Control is an LDAP Control [RFC4511] where the
+   controlType is the object identifier 1.3.6.1.4.1.4203.1.9.1.3 and the
+   controlValue contains a BER-encoded syncDoneValue.  The criticality
+   is FALSE (and hence absent).
+
+      syncDoneValue ::= SEQUENCE {
+          cookie          syncCookie OPTIONAL,
+          refreshDeletes  BOOLEAN DEFAULT FALSE
+      }
+
+   The Sync Done Control is only applicable to the SearchResultDone
+   Message.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Zeilenga & Choi               Experimental                     [Page 10]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+2.5.  Sync Info Message
+
+   The Sync Info Message is an LDAP Intermediate Response Message
+   [RFC4511] where responseName is the object identifier
+   1.3.6.1.4.1.4203.1.9.1.4 and responseValue contains a BER-encoded
+   syncInfoValue.  The criticality is FALSE (and hence absent).
+
+      syncInfoValue ::= CHOICE {
+          newcookie      [0] syncCookie,
+          refreshDelete  [1] SEQUENCE {
+              cookie         syncCookie OPTIONAL,
+              refreshDone    BOOLEAN DEFAULT TRUE
+          },
+          refreshPresent [2] SEQUENCE {
+              cookie         syncCookie OPTIONAL,
+              refreshDone    BOOLEAN DEFAULT TRUE
+          },
+          syncIdSet      [3] SEQUENCE {
+              cookie         syncCookie OPTIONAL,
+              refreshDeletes BOOLEAN DEFAULT FALSE,
+              syncUUIDs      SET OF syncUUID
+          }
+      }
+
+2.6.  Sync Result Codes
+
+   The following LDAP resultCode [RFC4511] is defined:
+
+      e-syncRefreshRequired (4096)
+
+3.  Content Synchronization
+
+   The Sync Operation is invoked when the client sends a SearchRequest
+   Message with a Sync Request Control.
+
+   The absence of a cookie or an initialized synchronization state in a
+   cookie indicates a request for initial content, while the presence of
+   a cookie representing a state of a client copy indicates a request
+   for a content update.  Synchronization Sessions are discussed in
+   Section 3.1.  Content Determination is discussed in Section 3.2.
+
+   The mode is either refreshOnly or refreshAndPersist.  The refreshOnly
+   and refreshAndPersist modes are discussed in Sections 3.3 and 3.4,
+   respectively.  The refreshOnly mode consists only of a refresh stage,
+   while the refreshAndPersist mode consists of a refresh stage and a
+   subsequent persist stage.
+
+
+
+
+
+Zeilenga & Choi               Experimental                     [Page 11]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+3.1.  Synchronization Session
+
+   A sequence of Sync Operations where the last cookie returned by the
+   server for one operation is provided by the client in the next
+   operation is said to belong to the same Synchronization Session.
+
+   The client MUST specify the same content-controlling parameters (see
+   Section 3.5) in each Search Request of the session.  The client
+   SHOULD also issue each Sync request of a session under the same
+   authentication and authorization associations with equivalent
+   integrity and protections.  If the server does not recognize the
+   request cookie or the request is made under different associations or
+   non-equivalent protections, the server SHALL return the initial
+   content as if no cookie had been provided or return an empty content
+   with the e-syncRefreshRequired LDAP result code.  The decision
+   between the return of the initial content and the return of the empty
+   content with the e-syncRefreshRequired result code MAY be based on
+   reloadHint in the Sync Request Control from the client.  If the
+   server recognizes the request cookie as representing empty or initial
+   synchronization state of the client copy, the server SHALL return the
+   initial content.
+
+   A Synchronization Session may span multiple LDAP sessions between the
+   client and the server.  The client SHOULD issue each Sync request of
+   a session to the same server.  (Note: Shadowing considerations are
+   discussed in Section 6.)
+
+3.2.  Content Determination
+
+   The content to be provided is determined by parameters of the Search
+   Request, as described in [RFC4511], and possibly other controls.  The
+   same content parameters SHOULD be used in each Sync request of a
+   session.  If different content is requested and the server is
+   unwilling or unable to process the request, the server SHALL return
+   the initial content as if no cookie had been provided or return an
+   empty content with the e-syncRefreshRequired LDAP result code.  The
+   decision between the return of the initial content and the return of
+   the empty content with the e-syncRefreshRequired result code MAY be
+   based on reloadHint in the Sync Request Control from the client.
+
+   The content may not necessarily include all entries or references
+   that would be returned by a normal search operation, nor, for those
+   entries included, all attributes returned by a normal search.  When
+   the server is unwilling or unable to provide synchronization for any
+   attribute for a set of entries, the server MUST treat all filter
+   components matching against these attributes as Undefined and MUST
+   NOT return these attributes in SearchResultEntry responses.
+
+
+
+
+Zeilenga & Choi               Experimental                     [Page 12]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+   Servers SHOULD support synchronization for all non-collective user-
+   application attributes for all entries.
+
+   The server may also return continuation references to other servers
+   or to itself.  The latter is allowed as the server may partition the
+   entries it holds into separate synchronization contexts.
+
+   The client may chase all or some of these continuations, each as a
+   separate content synchronization session.
+
+3.3.  refreshOnly Mode
+
+   A Sync request with mode refreshOnly and with no cookie is a poll for
+   initial content.  A Sync request with mode refreshOnly and with a
+   cookie representing a synchronization state is a poll for content
+   update.
+
+3.3.1.  Initial Content Poll
+
+   Upon receipt of the request, the server provides the initial content
+   using a set of zero or more SearchResultEntry and
+   SearchResultReference Messages followed by a SearchResultDone
+   Message.
+
+   Each SearchResultEntry Message SHALL include a Sync State Control of
+   state add, an entryUUID containing the entry's UUID, and no cookie.
+   Each SearchResultReference Message SHALL include a Sync State Control
+   of state add, an entryUUID containing the UUID associated with the
+   reference (normally the UUID of the associated named referral
+   [RFC3296] object), and no cookie.  The SearchResultDone Message SHALL
+   include a Sync Done Control having refreshDeletes set to FALSE.
+
+   A resultCode value of success indicates that the operation
+   successfully completed.  Otherwise, the result code indicates the
+   nature of the failure.  The server may return e-syncRefreshRequired
+   result code on the initial content poll if it is safe to do so when
+   it is unable to perform the operation due to various reasons.
+   reloadHint is set to FALSE in the SearchRequest Message requesting
+   the initial content poll.
+
+   If the operation is successful, a cookie representing the
+   synchronization state of the current client copy SHOULD be returned
+   for use in subsequent Sync Operations.
+
+3.3.2.  Content Update Poll
+
+   Upon receipt of the request, the server provides the content refresh
+   using a set of zero or more SearchResultEntry and
+
+
+
+Zeilenga & Choi               Experimental                     [Page 13]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+   SearchResultReference Messages followed by a SearchResultDone
+   Message.
+
+   The server is REQUIRED to:
+
+      a) provide the sequence of messages necessary for eventual
+         convergence of the client's copy of the content to the server's
+         copy,
+
+      b) treat the request as an initial content request (e.g., ignore
+         the cookie or the synchronization state represented in the
+         cookie),
+
+      c) indicate that the incremental convergence is not possible by
+         returning e-syncRefreshRequired,
+
+      d) return a resultCode other than success or e-
+         syncRefreshRequired.
+
+   A Sync Operation may consist of a single present phase, a single
+   delete phase, or a present phase followed by a delete phase.
+
+   In each phase, for each entry or reference that has been added to the
+   content or been changed since the previous Sync Operation indicated
+   by the cookie, the server returns a SearchResultEntry or
+   SearchResultReference Message, respectively, each with a Sync State
+   Control consisting of state add, an entryUUID containing the UUID of
+   the entry or reference, and no cookie.  Each SearchResultEntry
+   Message represents the current state of a changed entry.  Each
+   SearchResultReference Message represents the current state of a
+   changed reference.
+
+   In the present phase, for each entry that has not been changed since
+   the previous Sync Operation, an empty SearchResultEntry is returned
+   whose objectName reflects the entry's current DN, whose attributes
+   field is empty, and whose Sync State Control consists of state
+   present, an entryUUID containing the UUID of the entry, and no
+   cookie.  For each reference that has not been changed since the
+   previous Sync Operation, an empty SearchResultReference containing an
+   empty SEQUENCE OF LDAPURL is returned with a Sync State Control
+   consisting of state present, an entryUUID containing the UUID of the
+   entry, and no cookie.  No messages are sent for entries or references
+   that are no longer in the content.
+
+   Multiple empty entries with a Sync State Control of state present
+   SHOULD be coalesced into one or more Sync Info Messages of syncIdSet
+   value with refreshDeletes set to FALSE.  syncUUIDs contain a set of
+   UUIDs of the entries and references unchanged since the last Sync
+
+
+
+Zeilenga & Choi               Experimental                     [Page 14]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+   Operation.  syncUUIDs may be empty.  The Sync Info Message of
+   syncIdSet may contain a cookie to represent the state of the content
+   after performing the synchronization of the entries in the set.
+
+   In the delete phase, for each entry no longer in the content, the
+   server returns a SearchResultEntry whose objectName reflects a past
+   DN of the entry or is empty, whose attributes field is empty, and
+   whose Sync State Control consists of state delete, an entryUUID
+   containing the UUID of the deleted entry, and no cookie.  For each
+   reference no longer in the content, a SearchResultReference
+   containing an empty SEQUENCE OF LDAPURL is returned with a Sync State
+   Control consisting of state delete, an entryUUID containing the UUID
+   of the deleted reference, and no cookie.
+
+   Multiple empty entries with a Sync State Control of state delete
+   SHOULD be coalesced into one or more Sync Info Messages of syncIdSet
+   value with refreshDeletes set to TRUE.  syncUUIDs contain a set of
+   UUIDs of the entries and references that have been deleted from the
+   content since the last Sync Operation.  syncUUIDs may be empty.  The
+   Sync Info Message of syncIdSet may contain a cookie to represent the
+   state of the content after performing the synchronization of the
+   entries in the set.
+
+   When a present phase is followed by a delete phase, the two phases
+   are delimited by a Sync Info Message containing syncInfoValue of
+   refreshPresent, which may contain a cookie representing the state
+   after completing the present phase.  The refreshPresent contains
+   refreshDone, which is always FALSE in the refreshOnly mode of Sync
+   Operation because it is followed by a delete phase.
+
+   If a Sync Operation consists of a single phase, each phase and hence
+   the Sync Operation are marked as ended by a SearchResultDone Message
+   with Sync Done Control, which SHOULD contain a cookie representing
+   the state of the content after completing the Sync Operation.  The
+   Sync Done Control contains refreshDeletes, which is set to FALSE for
+   the present phase and set to TRUE for the delete phase.
+
+   If a Sync Operation consists of a present phase followed by a delete
+   phase, the Sync Operation is marked as ended at the end of the delete
+   phase by a SearchResultDone Message with Sync Done Control, which
+   SHOULD contain a cookie representing the state of the content after
+   completing the Sync Operation.  The Sync Done Control contains
+   refreshDeletes, which is set to TRUE.
+
+   The client can specify whether it prefers to receive an initial
+   content by supplying reloadHint of TRUE or to receive a e-
+   syncRefreshRequired resultCode by supplying reloadHint of FALSE
+   (hence absent), in the case that the server determines that it is
+
+
+
+Zeilenga & Choi               Experimental                     [Page 15]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+   impossible or inefficient to achieve the eventual convergence by
+   continuing the current incremental synchronization thread.
+
+   A resultCode value of success indicates that the operation is
+   successfully completed.  A resultCode value of e-syncRefreshRequired
+   indicates that a full or partial refresh is needed.  Otherwise, the
+   result code indicates the nature of failure.  A cookie is provided in
+   the Sync Done Control for use in subsequent Sync Operations for
+   incremental synchronization.
+
+3.4.  refreshAndPersist Mode
+
+   A Sync request with mode refreshAndPersist asks for initial content
+   or content update (during the refresh stage) followed by change
+   notifications (during the persist stage).
+
+3.4.1.  refresh Stage
+
+   The content refresh is provided as described in Section 3.3, except
+   that the successful completion of content refresh is indicated by
+   sending a Sync Info Message of refreshDelete or refreshPresent with a
+   refreshDone value set to TRUE instead of a SearchResultDone Message
+   with resultCode success.  A cookie SHOULD be returned in the Sync
+   Info Message to represent the state of the content after finishing
+   the refresh stage of the Sync Operation.
+
+3.4.2.  persist Stage
+
+   Change notifications are provided during the persist stage.
+
+   As updates are made to the DIT, the server notifies the client of
+   changes to the content.  DIT updates may cause entries and references
+   to be added to the content, deleted from the content, or modified
+   within the content.  DIT updates may also cause references to be
+   added, deleted, or modified within the content.
+
+   Where DIT updates cause an entry to be added to the content, the
+   server provides a SearchResultEntry Message that represents the entry
+   as it appears in the content.  The message SHALL include a Sync State
+   Control with state of add, an entryUUID containing the entry's UUID,
+   and an optional cookie.
+
+   Where DIT updates cause a reference to be added to the content, the
+   server provides a SearchResultReference Message that represents the
+   reference in the content.  The message SHALL include a Sync State
+   Control with state of add, an entryUUID containing the UUID
+   associated with the reference, and an optional cookie.
+
+
+
+
+Zeilenga & Choi               Experimental                     [Page 16]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+   Where DIT updates cause an entry to be modified within the content,
+   the server provides a SearchResultEntry Message that represents the
+   entry as it appears in the content.  The message SHALL include a Sync
+   State Control with state of modify, an entryUUID containing the
+   entry's UUID, and an optional cookie.
+
+   Where DIT updates cause a reference to be modified within the
+   content, the server provides a SearchResultReference Message that
+   represents the reference in the content.  The message SHALL include a
+   Sync State Control with state of modify, an entryUUID containing the
+   UUID associated with the reference, and an optional cookie.
+
+   Where DIT updates cause an entry to be deleted from the content, the
+   server provides a SearchResultEntry Message with no attributes.  The
+   message SHALL include a Sync State Control with state of delete, an
+   entryUUID containing the entry's UUID, and an optional cookie.
+
+   Where DIT updates cause a reference to be deleted from the content,
+   the server provides a SearchResultReference Message with an empty
+   SEQUENCE OF LDAPURL.  The message SHALL include a Sync State Control
+   with state of delete, an entryUUID containing the UUID associated
+   with the reference, and an optional cookie.
+
+   Multiple empty entries with a Sync State Control of state delete
+   SHOULD be coalesced into one or more Sync Info Messages of syncIdSet
+   value with refreshDeletes set to TRUE. syncUUIDs contain a set of
+   UUIDs of the entries and references that have been deleted from the
+   content.  The Sync Info Message of syncIdSet may contain a cookie to
+   represent the state of the content after performing the
+   synchronization of the entries in the set.
+
+   With each of these messages, the server may provide a new cookie to
+   be used in subsequent Sync Operations.  Additionally, the server may
+   also return Sync Info Messages of choice newCookie to provide a new
+   cookie.  The client SHOULD use the newest (last) cookie it received
+   from the server in subsequent Sync Operations.
+
+3.5.  Search Request Parameters
+
+   As stated in Section 3.1, the client SHOULD specify the same
+   content-controlling parameters in each Search Request of the session.
+   All fields of the SearchRequest Message are considered content-
+   controlling parameters except for sizeLimit and timeLimit.
+
+
+
+
+
+
+
+
+Zeilenga & Choi               Experimental                     [Page 17]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+3.5.1.  baseObject
+
+   As with the normal search operation, the refresh and persist stages
+   are not isolated from DIT changes.  It is possible that the entry
+   referred to by the baseObject is deleted, renamed, or moved.  It is
+   also possible that the alias object used in finding the entry
+   referred to by the baseObject is changed such that the baseObject
+   refers to a different entry.
+
+   If the DIT is updated during processing of the Sync Operation in a
+   manner that causes the baseObject no longer to refer to any entry or
+   in a manner that changes the entry the baseObject refers to, the
+   server SHALL return an appropriate non-success result code, such as
+   noSuchObject, aliasProblem, aliasDereferencingProblem, referral, or
+   e-syncRefreshRequired.
+
+3.5.2.  derefAliases
+
+   This operation does not support alias dereferencing during searching.
+   The client SHALL specify neverDerefAliases or derefFindingBaseObj for
+   the SearchRequest derefAliases parameter.  The server SHALL treat
+   other values (e.g., derefInSearching, derefAlways) as protocol
+   errors.
+
+3.5.3.  sizeLimit
+
+   The sizeLimit applies only to entries (regardless of their state in
+   Sync State Control) returned during the refreshOnly operation or the
+   refresh stage of the refreshAndPersist operation.
+
+3.5.4.  timeLimit
+
+   For a refreshOnly Sync Operation, the timeLimit applies to the whole
+   operation.  For a refreshAndPersist operation, the timeLimit applies
+   only to the refresh stage including the generation of the Sync Info
+   Message with a refreshDone value of TRUE.
+
+3.5.5.  filter
+
+   The client SHOULD avoid filter assertions that apply to the values of
+   the attributes likely to be considered by the server as ones holding
+   meta-information.  See Section 4.
+
+3.6.  objectName
+
+   The Sync Operation uses entryUUID values provided in the Sync State
+   Control as the primary keys to entries.  The client MUST use these
+   entryUUIDs to correlate synchronization messages.
+
+
+
+Zeilenga & Choi               Experimental                     [Page 18]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+   In some circumstances, the DN returned may not reflect the entry's
+   current DN.  In particular, when the entry is being deleted from the
+   content, the server may provide an empty DN if the server does not
+   wish to disclose the entry's current DN (or, if deleted from the DIT,
+   the entry's last DN).
+
+   Also note that the entry's DN may be viewed as meta information (see
+   Section 4.1).
+
+3.7.  Canceling the Sync Operation
+
+   Servers MUST implement the LDAP Cancel [RFC3909] Operation and
+   support cancellation of outstanding Sync Operations as described
+   here.
+
+   To cancel an outstanding Sync Operation, the client issues an LDAP
+   Cancel [RFC3909] Operation.
+
+   If at any time the server becomes unwilling or unable to continue
+   processing a Sync Operation, the server SHALL return a
+   SearchResultDone with a non-success resultCode indicating the reason
+   for the termination of the operation.
+
+   Whether the client or the server initiated the termination, the
+   server may provide a cookie in the Sync Done Control for use in
+   subsequent Sync Operations.
+
+3.8.  Refresh Required
+
+   In order to achieve the eventually-convergent synchronization, the
+   server may terminate the Sync Operation in the refresh or persist
+   stages by returning an e-syncRefreshRequired resultCode to the
+   client.  If no cookie is provided, a full refresh is needed.  If a
+   cookie representing a synchronization state is provided in this
+   response, an incremental refresh is needed.
+
+   To obtain a full refresh, the client then issues a new
+   synchronization request with no cookie.  To obtain an incremental
+   reload, the client issues a new synchronization with the provided
+   cookie.
+
+   The server may choose to provide a full copy in the refresh stage
+   (e.g., ignore the cookie or the synchronization state represented in
+   the cookie) instead of providing an incremental refresh in order to
+   achieve the eventual convergence.
+
+
+
+
+
+
+Zeilenga & Choi               Experimental                     [Page 19]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+   The decision between the return of the initial content and the return
+   of the e-syncRefreshRequired result code may be based on reloadHint
+   in the Sync Request Control from the client.
+
+   In the case of persist stage Sync, the server returns the resultCode
+   of e-syncRefreshRequired to the client to indicate that the client
+   needs to issue a new Sync Operation in order to obtain a synchronized
+   copy of the content.  If no cookie is provided, a full refresh is
+   needed.  If a cookie representing a synchronization state is
+   provided, an incremental refresh is needed.
+
+   The server may also return e-syncRefreshRequired if it determines
+   that a refresh would be more efficient than sending all the messages
+   required for convergence.
+
+   Note that the client may receive one or more of SearchResultEntry,
+   SearchResultReference, and/or Sync Info Messages before it receives a
+   SearchResultDone Message with the e-syncRefreshRequired result code.
+
+3.9.  Chattiness Considerations
+
+   The server MUST ensure that the number of entry messages generated to
+   refresh the client content does not exceed the number of entries
+   presently in the content.  While there is no requirement for servers
+   to maintain history information, if the server has sufficient history
+   to allow it to reliably determine which entries in the prior client
+   copy are no longer present in the content and the number of such
+   entries is less than or equal to the number of unchanged entries, the
+   server SHOULD generate delete entry messages instead of present entry
+   messages (see Section 3.3.2).
+
+   When the amount of history information maintained in the server is
+   not enough for the clients to perform infrequent refreshOnly Sync
+   Operations, it is likely that the server has incomplete history
+   information (e.g., due to truncation) by the time those clients
+   connect again.
+
+   The server SHOULD NOT resort to full reload when the history
+   information is not enough to generate delete entry messages.  The
+   server SHOULD generate either present entry messages only or present
+   entry messages followed by delete entry messages to bring the client
+   copy to the current state.  In the latter case, the present entry
+   messages bring the client copy to a state covered by the history
+   information maintained in the server.
+
+   The server SHOULD maintain enough (current or historical) state
+   information (such as a context-wide last modify time stamp) to
+   determine if no changes were made in the context since the content
+
+
+
+Zeilenga & Choi               Experimental                     [Page 20]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+   refresh was provided and, when no changes were made, generate zero
+   delete entry messages instead of present messages.
+
+   The server SHOULD NOT use the history information when its use does
+   not reduce the synchronization traffic or when its use can expose
+   sensitive information not allowed to be received by the client.
+
+   The server implementor should also consider chattiness issues that
+   span multiple Sync Operations of a session.  As noted in Section 3.8,
+   the server may return e-syncRefreshRequired if it determines that a
+   reload would be more efficient than continuing under the current
+   operation.  If reloadHint in the Sync Request is TRUE, the server may
+   initiate a reload without directing the client to request a reload.
+
+   The server SHOULD transfer a new cookie frequently to avoid having to
+   transfer information already provided to the client.  Even where DIT
+   changes do not cause content synchronization changes to be
+   transferred, it may be advantageous to provide a new cookie using a
+   Sync Info Message.  However, the server SHOULD avoid overloading the
+   client or network with Sync Info Messages.
+
+   During persist mode, the server SHOULD coalesce multiple outstanding
+   messages updating the same entry.  The server MAY delay generation of
+   an entry update in anticipation of subsequent changes to that entry
+   that could be coalesced.  The length of the delay should be long
+   enough to allow coalescing of update requests issued back to back but
+   short enough that the transient inconsistency induced by the delay is
+   corrected in a timely manner.
+
+   The server SHOULD use the syncIdSet Sync Info Message when there are
+   multiple delete or present messages to reduce the amount of
+   synchronization traffic.
+
+   Also note that there may be many clients interested in a particular
+   directory change, and that servers attempting to service all of these
+   at once may cause congestion on the network.  The congestion issues
+   are magnified when the change requires a large transfer to each
+   interested client.  Implementors and deployers of servers should take
+   steps to prevent and manage network congestion.
+
+3.10.  Operation Multiplexing
+
+   The LDAP protocol model [RFC4511] allows operations to be multiplexed
+   over a single LDAP session.  Clients SHOULD NOT maintain multiple
+   LDAP sessions with the same server.  Servers SHOULD ensure that
+   responses from concurrently processed operations are interleaved
+   fairly.
+
+
+
+
+Zeilenga & Choi               Experimental                     [Page 21]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+   Clients SHOULD combine Sync Operations whose result set is largely
+   overlapping.  This avoids having to return multiple messages, once
+   for each overlapping session, for changes to entries in the overlap.
+
+   Clients SHOULD NOT combine Sync Operations whose result sets are
+   largely non-overlapping.  This ensures that an event requiring an
+   e-syncRefreshRequired response can be limited to as few result sets
+   as possible.
+
+4.  Meta Information Considerations
+
+4.1.  Entry DN
+
+   As an entry's DN is constructed from its relative DN (RDN) and the
+   entry's parent's DN, it is often viewed as meta information.
+
+   While renaming or moving to a new superior causes the entry's DN to
+   change, that change SHOULD NOT, by itself, cause synchronization
+   messages to be sent for that entry.  However, if the renaming or the
+   moving could cause the entry to be added or deleted from the content,
+   appropriate synchronization messages should be generated to indicate
+   this to the client.
+
+   When a server treats the entry's DN as meta information, the server
+   SHALL either
+
+      -  evaluate all MatchingRuleAssertions [RFC4511] to TRUE if
+         matching a value of an attribute of the entry, otherwise
+         Undefined, or
+
+      -  evaluate all MatchingRuleAssertion with dnAttributes of TRUE as
+         Undefined.
+
+   The latter choice is offered for ease of server implementation.
+
+4.2.  Operational Attributes
+
+   Where values of an operational attribute are determined by values not
+   held as part of the entry it appears in, the operational attribute
+   SHOULD NOT support synchronization of that operational attribute.
+
+   For example, in servers that implement the X.501 subschema model
+   [X.501], servers should not support synchronization of the
+   subschemaSubentry attribute as its value is determined by values held
+   and administrated in subschema subentries.
+
+
+
+
+
+
+Zeilenga & Choi               Experimental                     [Page 22]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+   As a counter example, servers that implement aliases [RFC4512][X.501]
+   can support synchronization of the aliasedObjectName attribute as its
+   values are held and administrated as part of the alias entries.
+
+   Servers SHOULD support synchronization of the following operational
+   attributes: createTimestamp, modifyTimestamp, creatorsName,
+   modifiersName [RFC4512].  Servers MAY support synchronization of
+   other operational attributes.
+
+4.3.  Collective Attributes
+
+   A collective attribute is "a user attribute whose values are the same
+   for each member of an entry collection" [X.501].  Use of collective
+   attributes in LDAP is discussed in [RFC3671].
+
+   Modification of a collective attribute generally affects the content
+   of multiple entries, which are the members of the collection.  It is
+   inefficient to include values of collective attributes visible in
+   entries of the collection, as a single modification of a collective
+   attribute requires transmission of multiple SearchResultEntry (one
+   for each entry of the collection that the modification affected).
+
+   Servers SHOULD NOT synchronize collective attributes appearing in
+   entries of any collection.  Servers MAY support synchronization of
+   collective attributes appearing in collective attribute subentries.
+
+4.4.  Access and Other Administrative Controls
+
+   Entries are commonly subject to access and other administrative
+   Controls.  While portions of the policy information governing a
+   particular entry may be held in the entry, policy information is
+   often held elsewhere (in superior entries, in subentries, in the root
+   DSE, in configuration files, etc.).  Because of this, changes to
+   policy information make it difficult to ensure eventual convergence
+   during incremental synchronization.
+
+   Where it is impractical or infeasible to generate content changes
+   resulting from a change to policy information, servers may opt to
+   return e-syncRefreshRequired or to treat the Sync Operation as an
+   initial content request (e.g., ignore the cookie or the
+   synchronization state represented in the cookie).
+
+5.  Interaction with Other Controls
+
+   The Sync Operation may be used with:
+
+      - ManageDsaIT Control [RFC3296]
+
+
+
+
+Zeilenga & Choi               Experimental                     [Page 23]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+      - Subentries Control [RFC3672]
+
+   as described below.  The Sync Operation may be used with other LDAP
+   extensions as detailed in other documents.
+
+5.1.  ManageDsaIT Control
+
+   The ManageDsaIT Control [RFC3296] indicates that the operation acts
+   upon the DSA Information Tree and causes referral and other special
+   entries to be treated as object entries with respect to the
+   operation.
+
+5.2.  Subentries Control
+
+   The Subentries Control is used with the search operation "to control
+   the visibility of entries and subentries which are within scope"
+   [RFC3672].  When used with the Sync Operation, the subentries control
+   and other factors (search scope, filter, etc.) are used to determine
+   whether an entry or subentry appears in the content.
+
+6.  Shadowing Considerations
+
+   As noted in [RFC4511], some servers may hold shadow copies of entries
+   that can be used to answer search and comparison queries.  Such
+   servers may also support content synchronization requests.  This
+   section discusses considerations for implementors and deployers for
+   the implementation and deployment of the Sync operation in shadowed
+   directories.
+
+   While a client may know of multiple servers that are equally capable
+   of being used to obtain particular directory content from, a client
+   SHOULD NOT assume that each of these servers is equally capable of
+   continuing a content synchronization session.  As stated in Section
+   3.1, the client SHOULD issue each Sync request of a Sync session to
+   the same server.
+
+   However, through domain naming or IP address redirection or other
+   techniques, multiple physical servers can be made to appear as one
+   logical server to a client.  Only servers that are equally capable in
+   regards to their support for the Sync operation and that hold equally
+   complete copies of the entries should be made to appear as one
+   logical server.  In particular, each physical server acting as one
+   logical server SHOULD be equally capable of continuing a content
+   synchronization based upon cookies provided by any of the other
+   physical servers without requiring a full reload.  Because there is
+   no standard LDAP shadowing mechanism, the specification of how to
+   independently implement equally capable servers (as well as the
+   precise definition of "equally capable") is left to future documents.
+
+
+
+Zeilenga & Choi               Experimental                     [Page 24]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+   Note that it may be difficult for the server to reliably determine
+   what content was provided to the client by another server, especially
+   in the shadowing environments that allow shadowing events to be
+   coalesced.  For these servers, the use of the delete phase discussed
+   in Section 3.3.2 may not be applicable.
+
+7.  Security Considerations
+
+   In order to maintain a synchronized copy of the content, a client is
+   to delete information from its copy of the content as described
+   above.  However, the client may maintain knowledge of information
+   disclosed to it by the server separate from its copy of the content
+   used for synchronization.  Management of this knowledge is beyond the
+   scope of this document.  Servers should be careful not to disclose
+   information for content the client is not authorized to have
+   knowledge of and/or about.
+
+   While the information provided by a series of refreshOnly Sync
+   Operations is similar to that provided by a series of Search
+   Operations, persist stage may disclose additional information.  A
+   client may be able to discern information about the particular
+   sequence of update operations that caused content change.
+
+   Implementors should take precautions against malicious cookie
+   content, including malformed cookies or valid cookies used with
+   different security associations and/or protections in an attempt to
+   obtain unauthorized access to information.  Servers may include a
+   digital signature in the cookie to detect tampering.
+
+   The operation may be the target of direct denial-of-service attacks.
+   Implementors should provide safeguards to ensure the operation is not
+   abused.  Servers may place access control or other restrictions upon
+   the use of this operation.
+
+   Note that even small updates to the directory may cause a significant
+   amount of traffic to be generated to clients using this operation.  A
+   user could abuse its update privileges to mount an indirect denial of
+   service to these clients, other clients, and/or portions of the
+   network.  Servers should provide safeguards to ensure that update
+   operations are not abused.
+
+   Implementors of this (or any) LDAP extension should be familiar with
+   general LDAP security considerations [RFC4510].
+
+
+
+
+
+
+
+
+Zeilenga & Choi               Experimental                     [Page 25]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+8.  IANA Considerations
+
+   Registration of the following values have been completed by the IANA
+   [RFC4520].
+
+8.1.  Object Identifier
+
+   The OID arc 1.3.6.1.4.1.4203.1.9.1 was assigned [ASSIGN] by the
+   OpenLDAP Foundation, under its IANA-assigned private enterprise
+   allocation [PRIVATE], for use in this specification.
+
+8.2.  LDAP Protocol Mechanism
+
+   The IANA has registered the LDAP Protocol Mechanism described in this
+   document.
+
+      Subject: Request for LDAP Protocol Mechanism Registration
+      Object Identifier: 1.3.6.1.4.1.4203.1.9.1.1
+      Description: LDAP Content Synchronization Control
+      Person & email address to contact for further information:
+          Kurt Zeilenga <kurt@openldap.org>
+      Usage: Control
+      Specification: RFC 4533
+      Author/Change Controller: Kurt D. Zeilenga, Jong Hyuk Choi
+      Comments: none
+
+8.3.  LDAP Result Codes
+
+   The IANA has registered the LDAP Result Code described in this
+   document.
+
+      Subject: LDAP Result Code Registration
+      Person & email address to contact for further information:
+          Kurt Zeilenga <kurt@OpenLDAP.org>
+      Result Code Name: e-syncRefreshRequired (4096)
+      Specification: RFC 4533
+      Author/Change Controller: Kurt D. Zeilenga, Jong Hyuk Choi
+      Comments:  none
+
+9.  Acknowledgements
+
+   This document borrows significantly from the LDAP Client Update
+   Protocol [RFC3928], a product of the IETF LDUP working group.  This
+   document also benefited from Persistent Search [PSEARCH], Triggered
+   Search [TSEARCH], and Directory Synchronization [DIRSYNC] works.
+   This document also borrows from "Lightweight Directory Access
+   Protocol (v3)" [RFC2251].
+
+
+
+
+Zeilenga & Choi               Experimental                     [Page 26]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+10.  Normative References
+
+   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
+               Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+   [RFC3296]   Zeilenga, K., "Named Subordinate References in
+               Lightweight Directory Access Protocol (LDAP)
+               Directories", RFC 3296, July 2002.
+
+   [RFC3671]   Zeilenga, K., "Collective Attributes in the Lightweight
+               Directory Access Protocol (LDAP)", RFC 3671, December
+               2003.
+
+   [RFC3672]   Zeilenga, K., "Subentries in the Lightweight Directory
+               Access Protocol (LDAP)", RFC 3672, December 2003.
+
+   [RFC3909]   Zeilenga, K., "Lightweight Directory Access Protocol
+               (LDAP) Cancel Operation", RFC 3909, October 2004.
+
+   [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.
+
+   [RFC4530]   Zeilenga, K., "Lightweight Directory Access Protocol
+               (LDAP) entryUUID Operational Attribute", RFC 4530, June
+               2006.
+
+   [UUID]      International Organization for Standardization (ISO),
+               "Information technology - Open Systems Interconnection -
+               Remote Procedure Call", ISO/IEC 11578:1996
+
+   [X.501]     International Telecommunication Union - Telecommunication
+               Standardization Sector, "The Directory -- Models,"
+               X.501(1993) (also ISO/IEC 9594-2:1994).
+
+   [X.680]     International Telecommunication Union - Telecommunication
+               Standardization Sector, "Abstract Syntax Notation One
+               (ASN.1) - Specification of Basic Notation", X.680(1997)
+               (also ISO/IEC 8824-1:1998).
+
+
+
+
+
+Zeilenga & Choi               Experimental                     [Page 27]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+   [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(1997) (also ISO/IEC 8825-1:1998).
+
+11.  Informative References
+
+   [RFC2251]   Wahl, M., Howes, T., and S. Kille, "Lightweight Directory
+               Access Protocol (v3)", RFC 2251, December 1997.
+
+   [RFC3928]   Megginson, R., Ed., Smith, M., Natkovich, O., and J.
+               Parham, "Lightweight Directory Access Protocol (LDAP)
+               Client Update Protocol (LCUP)", RFC 3928, October 2004.
+
+   [RFC4520]   Zeilenga, K., "Internet Assigned Numbers Authority (IANA)
+               Considerations for the Lightweight Directory Access
+               Protocol (LDAP)", BCP 64, RFC 4520, June 2006.
+
+   [PRIVATE]   IANA, "Private Enterprise Numbers",
+               http://www.iana.org/assignments/enterprise-numbers.
+
+   [ASSIGN]    OpenLDAP Foundation, "OpenLDAP OID Delegations",
+               http://www.openldap.org/foundation/oid-delegate.txt.
+
+   [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.525]     International Telecommunication Union - Telecommunication
+               Standardization Sector, "The Directory: Replication",
+               X.525(1993).
+
+   [DIRSYNC]   Armijo, M., "Microsoft LDAP Control for Directory
+               Synchronization", Work in Progress.
+
+   [PSEARCH]   Smith, M., et al., "Persistent Search: A Simple LDAP
+               Change Notification Mechanism", Work in Progress.
+
+   [TSEARCH]   Wahl, M., "LDAPv3 Triggered Search Control", Work in
+               Progress.
+
+
+
+
+
+
+
+
+
+Zeilenga & Choi               Experimental                     [Page 28]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+Appendix A.  CSN-based Implementation Considerations
+
+   This appendix is provided for informational purposes only; it is not
+   a normative part of the LDAP Content Synchronization Operation's
+   technical specification.
+
+   This appendix discusses LDAP Content Synchronization Operation server
+   implementation considerations associated with Change Sequence Number
+   based approaches.
+
+   Change Sequence Number based approaches are targeted for use in
+   servers that do not maintain history information (e.g., change logs,
+   state snapshots) about changes made to the Directory and hence, must
+   rely on current directory state and minimal synchronization state
+   information embedded in Sync Cookie.  Servers that maintain history
+   information should consider other approaches that exploit the history
+   information.
+
+   A Change Sequence Number is effectively a time stamp that has
+   sufficient granularity to ensure that the precedence relationship in
+   time of two updates to the same object can be determined.  Change
+   Sequence Numbers are not to be confused with Commit Sequence Numbers
+   or Commit Log Record Numbers.  A Commit Sequence Number allows one to
+   determine how two commits (to the same object or different objects)
+   relate to each other in time.  A Change Sequence Number associated
+   with different entries may be committed out of order.  In the
+   remainder of this Appendix, the term CSN refers to a Change Sequence
+   Number.
+
+   In these approaches, the server not only maintains a CSN for each
+   directory entry (the entry CSN) but also maintains a value that we
+   will call the context CSN.  The context CSN is the greatest committed
+   entry CSN that is not greater than any outstanding (uncommitted)
+   entry CSNs for all entries in a directory context.  The values of
+   context CSN are used in syncCookie values as synchronization state
+   indicators.
+
+   As search operations are not isolated from individual directory
+   update operations and individual update operations cannot be assumed
+   to be serialized, one cannot assume that the returned content
+   incorporates each relevant change whose change sequence number is
+   less than or equal to the greatest entry CSN in the content.  The
+   content incorporates all the relevant changes whose change sequence
+   numbers are less than or equal to context CSN before search
+   processing.  The content may also incorporate any subset of the
+   changes whose change sequence number is greater than context CSN
+   before search processing but less than or equal to the context CSN
+   after search processing.  The content does not incorporate any of the
+
+
+
+Zeilenga & Choi               Experimental                     [Page 29]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+   changes whose CSN is greater than the context CSN after search
+   processing.
+
+   A simple server implementation could use the value of the context CSN
+   before search processing to indicate state.  Such an implementation
+   would embed this value into each SyncCookie returned.  We'll call
+   this the cookie CSN.  When a refresh was requested, the server would
+   simply generate "update" messages for all entries in the content
+   whose CSN is greater than the supplied cookie CSN and generate
+   "present" messages for all other entries in the content.  However, if
+   the current context CSN is the same as the cookie CSN, the server
+   should instead generate zero "updates" and zero "delete" messages and
+   indicate a refreshDeletes of TRUE, as the directory has not changed.
+
+   The implementation should also consider the impact of changes to meta
+   information, such as access controls, that affect content
+   determination.  One approach is for the server to maintain a
+   context-wide meta information CSN or meta CSN.  This meta CSN would
+   be updated whenever meta information affecting content determination
+   was changed.  If the value of the meta CSN is greater than the cookie
+   CSN, the server should ignore the cookie and treat the request as an
+   initial request for content.
+
+   Additionally, servers may want to consider maintaining some per-
+   session history information to reduce the number of messages needed
+   to be transferred during incremental refreshes.  Specifically, a
+   server could record information about entries as they leave the scope
+   of a disconnected sync session and later use this information to
+   generate delete messages instead of present messages.
+
+   When the history information is truncated, the CSN of the latest
+   truncated history information entry may be recorded as the truncated
+   CSN of the history information.  The truncated CSN may be used to
+   determine whether a client copy can be covered by the history
+   information by comparing it to the synchronization state contained in
+   the cookie supplied by the client.
+
+   When there is a large number of sessions, it may make sense to
+   maintain such history only for the selected clients.  Also, servers
+   taking this approach need to consider resource consumption issues to
+   ensure reasonable server operation and to protect against abuse.  It
+   may be appropriate to restrict this mode of operation by policy.
+
+
+
+
+
+
+
+
+
+Zeilenga & Choi               Experimental                     [Page 30]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+Authors' Addresses
+
+   Kurt D. Zeilenga
+   OpenLDAP Foundation
+
+   EMail: Kurt@OpenLDAP.org
+
+
+   Jong Hyuk Choi
+   IBM Corporation
+
+   EMail: jongchoi@us.ibm.com
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Zeilenga & Choi               Experimental                     [Page 31]
+
+RFC 4533         LDAP Content Synchronization Operation        June 2006
+
+
+Full Copyright Statement
+
+   Copyright (C) The Internet Society (2006).
+
+   This document is subject to the rights, licenses and restrictions
+   contained in BCP 78 and at www.rfc-editor.org/copyright.html, and
+   except as set forth therein, the authors retain all their rights.
+
+   This document and the information contained herein are provided on an
+   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
+   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
+   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
+   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
+   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
+   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
+
+Intellectual Property
+
+   The IETF takes no position regarding the validity or scope of any
+   Intellectual Property Rights 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; nor does it represent that it has
+   made any independent effort to identify any such rights.  Information
+   on the procedures with respect to rights in RFC documents can be
+   found in BCP 78 and BCP 79.
+
+   Copies of IPR disclosures made to the IETF Secretariat and any
+   assurances of licenses to be made available, or the result of an
+   attempt made to obtain a general license or permission for the use of
+   such proprietary rights by implementers or users of this
+   specification can be obtained from the IETF on-line IPR repository at
+   http://www.ietf.org/ipr.
+
+   The IETF invites any interested party to bring to its attention any
+   copyrights, patents or patent applications, or other proprietary
+   rights that may cover technology that may be required to implement
+   this standard.  Please address the information to the IETF at
+   ietf-ipr@ietf.org.
+
+Acknowledgement
+
+   Funding for the RFC Editor function is provided by the IETF
+   Administrative Support Activity (IASA).
+
+
+
+
+
+
+
+Zeilenga & Choi               Experimental                     [Page 32]
+