INTERNET-DRAFT Kurt D. Zeilenga Intended Category: Standard Track OpenLDAP Foundation Expires in six months Jonghyuk Choi IBM Corporation 5 May 2003 LDAP Content Synchronization Operation 1. Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Distribution of this memo is unlimited. Technical discussion of this document will take place on the IETF LDUP Working Group mailing list at . Please send editorial comments directly to the document editor at . Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as ``work in progress.'' The list of current Internet-Drafts can be accessed at . The list of Internet-Draft Shadow Directories can be accessed at . Copyright 2003, The Internet Society. All Rights Reserved. Please see the Copyright section near the end of this document for more information. Zeilenga LDAP Content Sync Operation [Page 1] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 Abstract This specification describes the LDAP (Lightweight Directory Access Protocol) Content Synchronization operation. The operation allows a client to maintain a shadow copy of a fragment of directory information tree. It supports both polling for changes and listening for changes. The operation is defined as an extension of the LDAP Search operation. 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]. 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 [RFC2251]. 1. Introduction The Lightweight Directory Access Protocol (LDAP) [RFC3377] provides a mechanism, the search operation [RFC2251], to allow a client to request the return of content matching a complex set of assertions and for the server to return this content, subject to access control and other restrictions, to the client. However, short of repeating a search operation each time a new copy needed, LDAP does not provide an effective and efficient mechanism for maintaining synchronized copies of directory content. This document defines the LDAP Content Synchronization operation, or Sync operation for short, which allows a client to maintain a synchronized shadow copy of a fragment of a Directory Information Tree (DIT). The Sync operation is defined as a set of controls and other protocol elements which extend the Search operation. 1.1. Background Over the years, a number of directory synchronization approaches have been suggested. These approaches are inadequate for one or more of the following reasons: 1) do not ensure a reasonable level of convergence; 2) fail to detect that convergence cannot be achieved (without Zeilenga LDAP Content Sync Operation [Page 2] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 reload); 3) require pre-arranged synchronization agreements; 4) require the server to maintain synchronization state on a per client basis; 5) require the server to maintain histories of past changes to DIT content and/or meta information; and/or 6) are overly chatty. The Sync operation provides eventual convergence of synchronized content when possible and, when not, notification that content reload is required. The Sync operation does not require pre-arranged synchronization agreements. The Sync operation does not require servers to maintain synchronization state on a per user basis. The Sync operation does not require servers to maintain any history of past changes to the DIT or to meta information. While histories (e.g., change logs, tombstones, DIT snapshots) may be used in the implementation of the Sync operation, the operation may be implemented using purely state-based approaches. As the Sync operation does not require servers to maintain any histories of past changes, it can be implemented in environments where it is not feasible to maintain such histories. Histories, if available, may be used by the server to reduce the number of messages generated and reduce their size. The Sync operation chattiness is reasonably bound. 1.2. Intended Usage The Sync operation is intended to be used in applications requiring eventual-convergent content synchronization. Upon completion of each synchronization phase of the operation, all information to construct an synchronized shadow copy of the content has been provided to the client or the client has been notified that a complete content reload is necessary. Excepting for transient inconsistencies due to concurrent operation (or other) processing at the server, the shadow copy is an accurate reflection of the content held by the server. Each inconsistency is transient in that it will be corrected during subsequent synchronization requests. Possible uses include: - White page service applications may use the Sync operation to Zeilenga LDAP Content Sync Operation [Page 3] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 maintain current shadow copy of a DIT fragment. For example, an mail user agent which use the sync operation to maintain a local copy of an enterprise address book. - Meta-information engines may use the Sync operation to maintain a shadow 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 Synchronization Protocol [X.525] which may be used for master-slave replication between LDAP servers. Other experimental LDAP replication protocols exist. The Sync operation should be viewed as complementary to these replication protocols. This protocol is not intended to be used in applications requiring transactional data consistency. As this protocol transfers all visible values of entries 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 basis ways the Sync operation can be used to maintain a synchronized shadow 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 shadow 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). 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 the entry. Unlike Zeilenga LDAP Content Sync Operation [Page 4] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 Distinguished Names (DNs), which may change over time, an entry's UUIDs are 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 shadow 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 was 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 which have changed with a Sync State control indicating state add. For each unchanged entry, the server sends an empty entry (e.g., no attributes) with a Sync State control indicating state present. The set of updates is followed by a searchResultDone with a Sync Done control. If the server can reliably determine which entries in the prior shadow 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 may, instead of returning an empty entry with state present for each present entry, send an empty entry with state delete for each entry which is no longer in the content. Also, the Sync Done control refreshDeletes is set to TRUE to indicate to the client that this method was used. This field is FALSE otherwise. The synchronized shadow copy of the DIT fragment is constructed by the client. If refreshDeletes 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 shadow content. They had been either deleted, moved, or otherwise scoped-out from the content. If refreshDeletes 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 those which were identified as having been deleted from the content. The client can, at some later time, re-poll for changes to this synchronized shadow copy. 1.3.2. Listening for Changes (refreshAndPersist) Polling for changes can be expensive in terms of server, client, and Zeilenga LDAP Content Sync Operation [Page 5] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 network resources. The refreshAndPersist mode allows for active updates of changed entries in the content. By selecting the refreshAndPersist mode, the client requests the server to send updates of entries that are changed after the the initial refresh content is determined. Instead of sending a searchResultDone message as described above, the server sends a Sync Info message to the client indicating that refresh phase is complete and then enters persist phase. After receipt of this Sync Info message, the client will have a synchronized shadow copy as described above. The server may then send change notifications. 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 with no attributes and a Sync State control indicating state delete. To modify entries in the return content, the server sends a searchResultEntry (with attributes) with a Sync State control indicating state modify. 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 a 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 any Sync State control or Sync Info message returned. The operation persists until canceled [CANCEL] by the client or terminated by the server. A Sync Done control may be attached to searchResultDone message to provide a new syncCookie. 2. Elements of the Sync Operation The Sync Operation is defined as an extension to the LDAP Search Operation [RFC2251] 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) responses with zero or more Zeilenga LDAP Content Sync Operation [Page 6] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 SearchResultEntry messages, each with a Sync State control; zero or more SearchResultReference messages, each with a Sync State control; zero or more Sync 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 the IANA-ASSIGNED-OID.1 as a value of supportedControl root DSE attribute. 2.1 Common ASN.1 elements 2.1.1 syncUUID The syncUUID is a notational convenience to indicate that, while the syncUUID type is encoded as an OCTET STRING, its value is restricted to the string representation of an Universally Unique Identifier (UUID) defined in [UUID]. syncUUID ::= OCTET STRING 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 which the server requires not be changed; the synchronization state information includes a commit (log) sequence number, a change sequence number, or a time stamp; and a digital signature for detection of tampering. syncCookie ::= OCTET STRING 2.2 Sync Request Control The Sync Request Control is an LDAP Control [RFC2251, Section 4.1.2] where the controlType is the object identifier IANA-ASSIGNED-OID.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 Zeilenga LDAP Content Sync Operation [Page 7] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 refreshAndPersist (3) }, cookie syncCookie OPTIONAL } The Sync Request Control is only applicable to the searchRequest message. 2.3 Sync State Control The Sync State Control is an LDAP Control [RFC2251, Section 4.1.2] where the controlType is the object identifier IANA-ASSIGNED-OID.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 [RFC2251, Section 4.1.2] where the controlType is the object identifier IANA-ASSIGNED-OID.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 SearchResultDone message. 2.5 Sync Info Message Zeilenga LDAP Content Sync Operation [Page 8] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 The Sync Info Message is an LDAP Intermediate Response Message [LDAPIRM] where responseName is the object identifier IANA-ASSIGNED-OID.4 and responseValue contains a BER-encoded syncInfoValue. The criticality is FALSE (and hence absent). syncInfoValue ::= CHOICE { newcookie [0] syncCookie, refreshDone [1] SEQUENCE { cookie syncCookie OPTIONAL, refreshDeletes BOOLEAN DEFAULT FALSE } } 2.6 Sync Result Codes The following LDAP resultCodes [RFC2251] are defined: syncRefreshRequired (IANA-ASSIGNED-CODE-0) 3. Content Synchronization The Sync Operation is invoked by the client sending a searchRequest message with a Sync Request Control. The absence of a cookie indicates a request for initial content while the presence of a cookie indicates a request for 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 Section 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. 3.1. Synchronization Session A sequence of Sync Operations where the last cookie returned by a operation is provided by the client in the next operation are 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 Zeilenga LDAP Content Sync Operation [Page 9] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 integrity and confidential protections. If the server does not recognize the request cookie or the request is made under different associations or inequivalent protections, the server SHALL process the request as if no cookie had been provided. 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. 3.2. Content Determination The content to be provided is determined by parameters of the Search Request, as described in [RFC2251], and possibly other controls. The same content 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 process the request as if no cookie had been provided. The content may not necessarily include all entries or references which would be returned by a normal search operation nor, for those entries included, not all attributes returned by a normal search. Where the server is unwilling or unable to provide synchronization for an attribute for a set of entries, the server MUST treat all filter components matching against these attribute as Undefined and MUST NOT return the attribute in searchResultEntry responses. Servers SHOULD support synchronization for all non-collective user-applications 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 in a separate LDAP session. 3.3. refreshOnly mode A Sync request with mode refreshOnly and no cookie is a poll for initial content. A Sync request with mode refreshOnly and cookie is a poll for content update. 3.3.1. Initial Content Poll Upon receipt of the request, the server provides the initial content Zeilenga LDAP Content Sync Operation [Page 10] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 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, entryUUID containing the entry's UUID, and no cookie. Each searchResultReference message SHALL include a Sync State control of state add, entryUUID containing the UUID associated with the reference (normally the referral [RFC3296] object's entryUUID), and no cookie. The searchResultDone message SHALL include a Sync Done control. The refreshDeletes SHALL be FALSE. A resultCode value of success indicates the operation successfully completed. Otherwise, the result code indicates the nature of failure. If the operation is successful, a cookie 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 searchResultReference messages followed by a searchResultDone message. The server is REQUIRED to either: 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), c) indicate that convergence is not possible by returning syncRefreshRequired, d) return a resultCode other than success or syncRefreshRequired. For each entry or reference added to the content or was changed since the previous Sync operation indicated by the cookie, the server returns a searchResultEntry or searchResultReference message, respectively, each with a Sync State cookie of state add, 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. For each entry which has not been changed since the previous Sync Zeilenga LDAP Content Sync Operation [Page 11] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 operation, a searchResultEntry is returned whose objectName reflects the entry's current DN, the attributes field is empty, and a Sync State control of state present, entryUUID containing the UUID of the entry, and no cookie. For each reference which has not been changed since the previous Sync operation, a searchResultReference containing an empty SEQUENCE OF LDAPURL is returned with a Sync State control of state present, entryUUID containing the UUID of the entry, and no cookie. No messages are sent for entries or references which are no longer in content. As an alternative to sending messages for each entry and reference which has not been changed, the server may instead return the following. For each entry no longer in content, return a searchResultEntry whose objectName reflects a past DN of the entry or is empty, the attributes field is empty, and a Sync State control of state delete, entryUUID containing the UUID of the deleted entry, and no cookie. For each reference no longer in content, a searchResultReference containing an empty SEQUENCE OF LDAPURL is returned with a a Sync State control of state delete, entryUUID containing the UUID of the deleted reference, and no cookie. A resultCode value of success indicates the operation successfully completed. Otherwise, the result code indicates the nature of failure. If the operation is successful, a cookie SHOULD be returned for use in subsequent Sync operations. 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 excepting that successful completion of content refresh is indicated by sending a Sync Info with state refreshDone message instead of a SearchResultDone message with resultCode success. A cookie SHOULD be returned for use in subsequent Sync operations. 3.4.2. persist stage Change notifications are provided during the persist stage. Zeilenga LDAP Content Sync Operation [Page 12] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 As updates are made to the DIT the server notifies the client of changes to the content. DIT updates may cause entries references to be added to the content, deleted from the content, or modify entries in 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 which represents the entry as it appears in the content. The message SHALL include a Sync State control with state of add, 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 which represents the reference in the content. The message SHALL include a Sync State control with state of add, entryUUID containing the UUID associated with the reference, and an optional cookie. Where DIT updates cause an entry to be modified in the content, the server provides a searchResultEntry message which represents the entry as it appears in the content. The message SHALL include a Sync State control with state of modify, entryUUID containing the entry's UUID, and an optional cookie. Where DIT updates cause a reference to be modified in the content, the server provides a searchResultEntry message which represents the reference in the content. The message SHALL include a Sync State control with state of modify, 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 searchResultReference message with an empty SEQUENCE OF LDAPURL. The message SHALL include a Sync State control with state of delete, entryUUID containing the UUID associated with the reference, and an optional cookie. Where DIT updates cause a reference 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, entryUUID containing the entry's UUID, and an optional cookie. 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 newest (last) cookie it received from the server in subsequent Sync operations. Zeilenga LDAP Content Sync Operation [Page 13] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 3.5. Search Request Parameters As stated in Section 3.1, the client SHOULD specify the same content controlling parameters (see Section 3.5) in each Search Request of the session. All fields of the SearchRequest message are considered content controlling parameters except for sizeLimit and timeLimit. 3.5.1. baseObject Issues As with the normal search operation, the refresh and persist phases are not isolated from DIT changes. It is possible that the entry referred to be the baseObject be deleted, renamed, or moved. It is also possible that 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 to no longer refers to any entry or changes which entry the baseObject refers to, the server SHALL return an appropriate non-success result code such as noSuchObject, aliasProblem, aliasDereferencingProblem, referral, or syncRefreshRequired. 3.5.2. derefAliases Issues 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 Issues The sizeLimit applies only to entries (regardless of their syncState) returned during refreshOnly processing or the refresh stage of the refreshAndPersist processing. 3.5.4. timeLimit Issues For a refreshOnly Sync operation, the timeLimit applies to the whole operation. For a refreshAndPersist operation, the timeLimit applies to processing up to and including generating the Sync Info with state refreshDone message. Zeilenga LDAP Content Sync Operation [Page 14] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 3.5.5. filter Issues The client SHOULD avoid filter assertions which apply to values of attributes likely to be considered by the server as holding meta- information. See section 4. 3.6. objectName Issues 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. 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). It should also be noted that the entry's DN may be viewed as meta information (see section 4.1). 3.7. Canceling the Sync Operation Servers SHOULD implement the LDAP Cancel [CANCEL] operation and support cancellation of outstanding Sync operations as described here. To cancel an outstanding Sync Operation, the client SHOULD issue a Cancel operation [CANCEL].... 3.7. Refresh Required In order to achieve the eventual-convergent synchronization, the server may terminate the Sync operation in refresh or persist stage by returning a syncRefreshRequired resultCode to the client. The client may then request a full reload (e.g., no cookie) instead of incremental synchronization in order to obtain a new copy of the content. In case that the client issues incremental synchronization requests between the issue of a syncRefreshRequired and that of a full reload, the server should send a syncRefreshRequired response again, but the client may receive one or more searchResultEntry responses before it receives the syncRefreshRequired response. The server may also choose to provide a full copy in the refresh stage (e.g., ignore the cookie) instead of providing an incremental refresh in order to achieve the eventual convergence. Zeilenga LDAP Content Sync Operation [Page 15] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 In the case of persist stage Sync, the server returns the resultCode of syncRefreshRequired to the client to indicate that the client needs to issue a full reload operation (e.g., no cookie) in order to obtain a synchronized copy of the content. The server may also return syncRefreshRequired if it determines that a refresh would be more efficient than sending all the messages required for convergence. 3.8. 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 historical information, if the server has sufficient history to allow it to reliably determine which entries in the prior shadow copy are no longer present in the content and the number of such entries is less than equal the number of unchanged entries, the server SHOULD generate delete entry messages instead of present entry messages (see Section 3.3.2). The server SHOULD maintain enough (current or historical) state information (such as a context-wide last modify time stamp), to determine that no changes were made in the context since the content to refresh was provided and, and when no changes were made, generate zero delete entry messages instead of present messages. The server implementor should also consider chattiness issues which span multiple Sync operations of a session. As noted in Section 3.7, the server may return syncRefreshRequired if it determines that a refresh would be more efficient than continuing under the current operation. 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 which 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. Zeilenga LDAP Content Sync Operation [Page 16] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 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 a superior to an entry causes the entry's DN to change, that change SHOULD NOT, by itself, cause synchronization message to be sent for that entry. However, if renaming or moving of a superior could cause the entry to added or deleted from the content and, if so, appropriate synchronization messages should be generated to indicate this to the client. Where a server treats the entry's DN as meta information, the server SHALL either - evaluate all MatchingRuleAssertions to TRUE if matching a value of an attribute of the entry and 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 is 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 which implement 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. For a counter example, servers which implement aliases [RFC2256][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 [RFC2252]. Servers MAY support synchronization of other operational attributes. Synchronization of operational attributes is discussed in Section 4.1. 4.3. Collective Attributes Zeilenga LDAP Content Sync Operation [Page 17] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 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 detailed in [COLLECTIVE]. Modification of a collective attribute generally affects the content of multiple entries, each a member 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 require transmission of multiple SearchResultEntry (one of each entry of the collection which the modification affected) to be transmitted. 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, ...). 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 syncRefreshRequired or treat the Sync Operation as an initial content request (e.g., ignore the cookie). 5. Interaction with other controls The Sync Operation may be used with: - ManageDsaIT Control [RFC3296] - Subentries Control [SUBENTRY] 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 Zeilenga LDAP Content Sync Operation [Page 18] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 objects to be treated as normal objects 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" [SUBENTRY]. When used with the Sync Operation, the subentries control and other factors (search scope, filter, etc.) are used to determining whether an entry or subentry appear in the content or not. 6. 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. 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 which 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 attempt to obtain unauthorized access to information. The Sync operation may be the target of denial of service attacks. Implementors should provide safeguards to ensure these mechanisms are not abused. Servers may place access control or other restrictions upon the use of this operation. Implementors of this (or any) LDAP extension should be familiar with general LDAP security considerations [RFC3377]. 7. IANA Considerations Registration of the following values is requested. 7.1. Object Identifier Zeilenga LDAP Content Sync Operation [Page 19] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 It is requested that IANA register upon Standards Action an LDAP Object Identifier to identify elements of the LDAP Content Synchronization Operation as defined in this document. Subject: Request for LDAP Object Identifier Registration Person & email address to contact for further information: Kurt Zeilenga Specification: RFCXXXX Author/Change Controller: IESG Comments: Identifies elements of the LDAP Content Synchronization Operation 7.2. LDAP Protocol Mechanism It is requested that IANA register upon Standards Action the LDAP Protocol Mechanism described in this document. Subject: Request for LDAP Protocol Mechanism Registration Object Identifier: IANA-ASSIGNED-OID Description: LDAP Content Synchronization Control Person & email address to contact for further information: Kurt Zeilenga Usage: Control Specification: RFCXXXX Author/Change Controller: IESG Comments: none 7.3. LDAP Result Codes It is requested that IANA register upon Standards Action the LDAP Result Codes described in this document. Subject: LDAP Result Code Registration Person & email address to contact for further information: Kurt Zeilenga Result Code Name: syncRefreshRequired (IANA-ASSIGNED-CODE-0) Specification: RFCXXXX Author/Change Controller: IESG Comments: none 8. Acknowledgment This work borrows significantly from the LDAP Client Update Protocol [LCUP]. This work also benefited Persistent Search [PSEARCH], Triggered Search [TSEARCH], and Directory Synchronization [DIRSYNC] Zeilenga LDAP Content Sync Operation [Page 20] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 efforts. This work also borrows from "Lightweight Directory Access Protocol (v3)" [RFC2251]. 9. Normative References [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14 (also RFC 2119), March 1997. [RFC2251] M. Wahl, T. Howes, S. Kille, "Lightweight Directory Access Protocol (v3)", RFC 2251, December 1997. [RFC2252] M. Wahl, A. Coulbeck, T. Howes, S. Kille, "Lightweight Directory Access Protocol (v3): Attribute Syntax Definitions", RFC 2252, December 1997. [RFC2256] M. Wahl, "A Summary of the X.500(96) User Schema for use with LDAPv3", RFC 2256, December 1997. [RFC2830] J. Hodges, R. Morgan, and M. Wahl, "Lightweight Directory Access Protocol (v3): Extension for Transport Layer Security", RFC 2830, May 2000. [RFC3296] K. Zeilenga, "Named Subordinate References in Lightweight Directory Access Protocol (LDAP) Directories", RFC 3296, July 2002. [RFC3377] J. Hodges, R.L. Morgan, "Lightweight Directory Access Protocol (v3): Technical Specification", RFC 3377, September 2002. [LDAPIRM] R. Harrison, K. Zeilenga, "LDAP Intermediate Response Message", draft-rharrison-ldap-intermediate-resp-xx.txt (a work in progress). [SUBENTRY] K. Zeilenga, S. Legg, "Subentries in LDAP", draft-zeilenga-ldap-subentry-xx.txt, a work in progress. [X.680] ITU-T, "Abstract Syntax Notation One (ASN.1) - Specification of Basic Notation", X.680, 1994. [X.690] ITU-T, "Specification of ASN.1 encoding rules: Basic, Canonical, and Distinguished Encoding Rules", X.690, 1994. [CANCEL] K. Zeilenga, "LDAP Cancel Extended Operation", draft-zeilenga-ldap-cancel-xx.txt, a work in progress. Zeilenga LDAP Content Sync Operation [Page 21] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 [UUID] International Organization for Standardization (ISO), "Information technology - Open Systems Interconnection - Remote Procedure Call", ISO/IEC 11578:1996. 10. Informative References [RFC3383] K. Zeilenga, "IANA Considerations for LDAP", BCP 64 (also RFC 3383), September 2002. [X.500] ITU-T Rec. X.500, "The Directory: Overview of Concepts, Models and Service", 1993. [X.511] ITU, "The Directory: Abstract Service Definition", ITU-T Rec. X.511, 1993. [X.525] ITU, "The Directory: Replication", ITU-T Rec. X.525, 1993. [COLLECTIVE] K. Zeilenga, "Collective Attributes in LDAP", draft-zeilenga-ldap-collective-xx.txt, a work in progress. [DIRSYNC] M. Armijo, "Microsoft LDAP Control for Directory Synchronization", draft-armijo-ldap-dirsync-xx.txt, a work in progress. [LCUP] R. Megginson, et. al., "LDAP Client Update Protocol", draft-ietf-ldup-lcup-xx.txt, a work in progress. [PSEARCH] M. Smith, et. al., "Persistent Search: A Simple LDAP Change Notification Mechanism", draft-ietf-ldapext-psearch-xx.txt, a work in progress. [TSEARCH] M. Wahl, "LDAPv3 Triggered Search Control", draft-ietf-ldapext-trigger-xx.txt, a work in progress. [UUID-CSN] K. Zeilenga, J. Choi, "LDAP UUID and CSN Operational Attributes", draft-zeilenga-ldap-uuid-csn-xx.txt, a work (not yet) in progress. 10. Authors' Address Kurt D. Zeilenga OpenLDAP Foundation Zeilenga LDAP Content Sync Operation [Page 22] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 Jonghyuk Choi IBM Corporation Full Copyright Copyright 2003, The Internet Society. All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE AUTHORS, THE INTERNET SOCIETY, AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS 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. Appendix - 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 some of the implementation considerations associated with a Change Sequence Number [UUID-CSN] based approaches to supporting the LDAP Content Synchronization Operation. Change Sequence Number-based approaches are targetted for use in servers which do not maintain historical information (e.g., change logs, state snapshots, etc.) about changes made to the Directory and hence, must rely on current directory state and minimal synchronization state information embedded in Sync Cookie. Servers Zeilenga LDAP Content Sync Operation [Page 23] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 which maintain historical information should consider an other approaches which exploit the historical information. A Change Sequence Number is, effectively a time stamp has sufficient granularity to ensure that 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 allow one to determine how to two commits (to the same object or different objects) relate to each other in time. 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 an entry CSN operational attribute for each directory entry (as discussed in [UUID- CSN], but maintains a value which we will call the context CSN. The context CSN is the greatest committed entry CSN which is not greater than any outstanding 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 all relevant changes 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 number is less than or equal to context CSN before search processing. The content may also incorporate any subset of the 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 changes whose CSN is greater than the context CSN after search processing. A simple server implementation could use 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 entry "update" messages for all entries in the content whose CSN is greater than the cookie CSN and entry "present" messages for all other entries in the content. However, if the current context CSN is same as the cookie CSN, the server should instead generate zero "updates", zero "delete" messages and indicate 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, which affects content determination. One approach is for the server to maintain a context Zeilenga LDAP Content Sync Operation [Page 24] INTERNET-DRAFT draft-zeilenga-ldup-sync-02 5 May 2003 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 cookie CSN, the server should ignore the cookie and treat the request as an initial request for content. Zeilenga LDAP Content Sync Operation [Page 25]