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Internet-Draft                                  Editor:  J. Sermersheim
Intended Category: Standard Track                           Novell, Inc
Document: draft-ietf-ldapbis-protocol-25.txt                  July 2004
Obsoletes: RFCs 2251, 2830, 3771


                            LDAP: The Protocol


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   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
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   Distribution of this memo is unlimited. Technical discussion of this
   document will take place on the IETF LDAP Revision Working Group
   (LDAPbis) mailing list <ietf-ldapbis@openldap.org>. Please send
   editorial comments directly to the editor <jimse@novell.com>.


Abstract

   This document describes the protocol elements, along with their
   semantics and encodings, of the Lightweight Directory Access Protocol
   (LDAP). LDAP provides access to distributed directory services that
   act in accordance with X.500 data and service models. These protocol
   elements are based on those described in the X.500 Directory Access
   Protocol (DAP).


Table of Contents

   1. Introduction....................................................2
   1.1. Relationship to Obsolete Specifications.......................3
   2. Conventions.....................................................3
   3. Protocol Model..................................................4
   3.1 Operation and LDAP Exchange Relationship.......................4
   4. Elements of Protocol............................................4
   4.1. Common Elements...............................................5
   4.1.1. Message Envelope............................................5

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   4.1.2. String Types................................................6
   4.1.3. Distinguished Name and Relative Distinguished Name..........7
   4.1.4. Attribute Descriptions......................................7
   4.1.5. Attribute Value.............................................7
   4.1.6. Attribute Value Assertion...................................8
   4.1.7. Attribute and PartialAttribute..............................8
   4.1.8. Matching Rule Identifier....................................9
   4.1.9. Result Message..............................................9
   4.1.10. Referral..................................................10
   4.1.11. Controls..................................................12
   4.2. Bind Operation...............................................14
   4.3. Unbind Operation.............................................16
   4.4. Unsolicited Notification.....................................17
   4.5. Search Operation.............................................18
   4.6. Modify Operation.............................................26
   4.7. Add Operation................................................28
   4.8. Delete Operation.............................................29
   4.9. Modify DN Operation..........................................29
   4.10. Compare Operation...........................................31
   4.11. Abandon Operation...........................................31
   4.12. Extended Operation..........................................32
   4.13. IntermediateResponse Message................................33
   4.13.1. Usage with LDAP ExtendedRequest and ExtendedResponse......34
   4.13.2. Usage with LDAP Request Controls..........................34
   4.14. StartTLS Operation..........................................35
   5. Protocol Encoding, Connection, and Transfer....................37
   5.2. Protocol Encoding............................................38
   5.3. Transmission Control Protocol (TCP)..........................38
   6. Security Considerations........................................38
   7. Acknowledgements...............................................40
   8. Normative References...........................................40
   9. Informative References.........................................41
   10. IANA Considerations...........................................42
   11. Editor's Address..............................................42
   Appendix A - LDAP Result Codes....................................43
   A.1 Non-Error Result Codes........................................43
   A.2 Result Codes..................................................43
   Appendix B - Complete ASN.1 Definition............................48
   Appendix C - Changes..............................................54
   C.1 Changes made to RFC 2251:.....................................54
   C.2 Changes made to RFC 2830:.....................................59
   C.3 Changes made to RFC 3771:.....................................60


1. Introduction

   The Directory is "a collection of open systems cooperating to provide
   directory services" [X.500]. A directory user, which may be a human
   or other entity, accesses the Directory through a client (or
   Directory User Agent (DUA)). The client, on behalf of the directory
   user, interacts with one or more servers (or Directory System Agents
   (DSA)). Clients interact with servers using a directory access
   protocol.


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   This document details the protocol elements of the Lightweight
   Directory Access Protocol (LDAP), along with their semantics.
   Following the description of protocol elements, it describes the way
   in which the protocol elements are encoded and transferred.


1.1. Relationship to Obsolete Specifications

   This document is an integral part of the LDAP Technical Specification
   [Roadmap] which obsoletes the previously defined LDAP technical
   specification, RFC 3377, in its entirety.

   This document obsoletes all of RFC 2251 except the following:
   Sections 3.2, 3.4, 4.1.3 (last paragraph), 4.1.4, 4.1.5, 4.1.5.1,
   4.1.9 (last paragraph), 5.1, 6.1, and 6.2 (last paragraph) are
   obsoleted by [Models].
   Section 3.3 is obsoleted by [Roadmap].
   Sections 4.2.1 (portions), and 4.2.2 are obsoleted by [AuthMeth].

   Appendix C.1 summarizes substantive changes to the remaining
   sections.

   This document obsoletes RFC 2830, Sections 2 and 4 in entirety. The
   remainder of RFC 2830 is obsoleted by [AuthMeth]. Appendix C.2
   summarizes substantive changes to the remaining sections.

   This document also obsoletes RFC 3771 in entirety.


2. Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", and "MAY" in this document are
   to be interpreted as described in [Keyword].

   The term "connection" refers to the underlying transport service used
   to carry the protocol exchange.

   The term "LDAP exchange" refers to application layer where LDAP PDUs
   are exchanged between protocol peers.

   The term "TLS layer" refers to a layer inserted between the
   connection and the LDAP exchange that utilizes [TLS] to protect the
   exchange of LDAP PDUs.

   The term "SASL layer" refers to a layer inserted between the
   connection and the LDAP exchange that utilizes [SASL] to protect the
   exchange of LDAP PDUs.

   See the table in Section 5 for an illustration of these four terms.

   The term "TLS-protected LDAP exchange" refers to an LDAP exchange
   protected by a TLS-layer.


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   The term "association" refers to the association of the LDAP exchange
   and its current authentication and authorization state.


3. Protocol Model

   The general model adopted by this protocol is one of clients
   performing protocol operations against servers. In this model, a
   client transmits a protocol request describing the operation to be
   performed to a server. The server is then responsible for performing
   the necessary operation(s) in the Directory. Upon completion of an
   operation, the server typically returns a response containing
   appropriate data to the requesting client.

   Although servers are required to return responses whenever such
   responses are defined in the protocol, there is no requirement for
   synchronous behavior on the part of either clients or servers.
   Requests and responses for multiple operations generally may be
   exchanged between a client and server in any order, provided the
   client eventually receives a response for every request that requires
   one.

   The core protocol operations defined in this document can be mapped
   to a subset of the X.500 (1993) Directory Abstract Service [X.511].
   However there is not a one-to-one mapping between LDAP operations and
   X.500 Directory Access Protocol (DAP) operations. Server
   implementations acting as a gateway to X.500 directories may need to
   make multiple DAP requests to service a single LDAP request.


3.1 Operation and LDAP Exchange Relationship

   Protocol operations are tied to an LDAP exchange. If the connection
   is closed, any uncompleted operations tied to the LDAP exchange are,
   when possible, abandoned, and when not possible, completed without
   transmission of the response. Also, if the connection is closed, the
   client MUST NOT assume that any uncompleted update operations tied to
   the LDAP exchange have succeeded or failed.


4. Elements of Protocol

   The protocol is described using Abstract Syntax Notation One
   ([ASN.1]), and is transferred using a subset of ASN.1 Basic Encoding
   Rules ([BER]). Section 5 specifies how the protocol elements are
   encoded and transferred.

   In order to support future extensions to this protocol, extensibility
   is implied where it is allowed per ASN.1 (i.e. sequence, set, choice,
   and enumerated types are extensible). In addition, ellipses (...)
   have been supplied in ASN.1 types that are explicitly extensible as
   discussed in [LDAPIANA]. Because of the implied extensibility,
   clients and servers MUST (unless otherwise specified) ignore trailing
   SEQUENCE components whose tags they do not recognize.

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   Changes to the protocol other than through the extension mechanisms
   described here require a different version number. A client indicates
   the version it is using as part of the bind request, described in
   Section 4.2. If a client has not sent a bind, the server MUST assume
   the client is using version 3 or later.

   Clients may determine the protocol versions a server supports by
   reading the 'supportedLDAPVersion' attribute from the root DSE (DSA-
   Specific Entry) [Models].


4.1. Common Elements

   This section describes the LDAPMessage envelope Protocol Data Unit
   (PDU) format, as well as data type definitions, which are used in the
   protocol operations.


4.1.1. Message Envelope

   For the purposes of protocol exchanges, all protocol operations are
   encapsulated in a common envelope, the LDAPMessage, which is defined
   as follows:

        LDAPMessage ::= SEQUENCE {
             messageID       MessageID,
             protocolOp      CHOICE {
                  bindRequest           BindRequest,
                  bindResponse          BindResponse,
                  unbindRequest         UnbindRequest,
                  searchRequest         SearchRequest,
                  searchResEntry        SearchResultEntry,
                  searchResDone         SearchResultDone,
                  searchResRef          SearchResultReference,
                  modifyRequest         ModifyRequest,
                  modifyResponse        ModifyResponse,
                  addRequest            AddRequest,
                  addResponse           AddResponse,
                  delRequest            DelRequest,
                  delResponse           DelResponse,
                  modDNRequest          ModifyDNRequest,
                  modDNResponse         ModifyDNResponse,
                  compareRequest        CompareRequest,
                  compareResponse       CompareResponse,
                  abandonRequest        AbandonRequest,
                  extendedReq           ExtendedRequest,
                  extendedResp          ExtendedResponse,
                  ...,
                  intermediateResponse  IntermediateResponse },
             controls       [0] Controls OPTIONAL }

        MessageID ::= INTEGER (0 .. maxInt)


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        maxInt INTEGER ::= 2147483647 -- (2^^31 - 1) --

   The ASN.1 type Controls is defined in Section 4.1.11.

   The function of the LDAPMessage is to provide an envelope containing
   common fields required in all protocol exchanges. At this time the
   only common fields are the message ID and the controls.

   If the server receives a PDU from the client in which the LDAPMessage
   SEQUENCE tag cannot be recognized, the messageID cannot be parsed,
   the tag of the protocolOp is not recognized as a request, or the
   encoding structures or lengths of data fields are found to be
   incorrect, then the server SHOULD return the Notice of Disconnection
   described in Section 4.4.1, with the resultCode set to protocolError,
   and MUST immediately close the connection.

   In other cases where the client or server cannot parse a PDU, it
   SHOULD abruptly close the connection where further communication
   (including providing notice) would be pernicious. Otherwise, server
   implementations MUST return an appropriate response to the request,
   with the resultCode set to protocolError.


4.1.1.1. Message ID

   All LDAPMessage envelopes encapsulating responses contain the
   messageID value of the corresponding request LDAPMessage.

   The message ID of a request MUST have a non-zero value different from
   the values of any other uncompleted requests in the LDAP association
   of which this message is a part. The zero value is reserved for the
   unsolicited notification message.

   Typical clients increment a counter for each request.

   A client MUST NOT send a request with the same message ID as an
   earlier request on the same LDAP association unless it can be
   determined that the server is no longer servicing the earlier request
   (e.g. after the final response is received, or a subsequent bind
   completes). Otherwise the behavior is undefined. For this purpose,
   note that abandon and abandoned operations do not send responses.


4.1.2. String Types

   The LDAPString is a notational convenience to indicate that, although
   strings of LDAPString type encode as ASN.1 OCTET STRING types, the
   [ISO10646] character set (a superset of [Unicode]) is used, encoded
   following the [UTF-8] algorithm. Note that Unicode characters U+0000
   through U+007F are the same as ASCII 0 through 127, respectively, and
   have the same single octet UTF-8 encoding.  Other Unicode characters
   have a multiple octet UTF-8 encoding.

        LDAPString ::= OCTET STRING -- UTF-8 encoded,

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                                    -- [ISO10646] characters

   The LDAPOID is a notational convenience to indicate that the
   permitted value of this string is a (UTF-8 encoded) dotted-decimal
   representation of an OBJECT IDENTIFIER. Although an LDAPOID is
   encoded as an OCTET STRING, values are limited to the definition of
   <numericoid> given in Section 1.4 of [Models].

        LDAPOID ::= OCTET STRING -- Constrained to <numericoid> [Models]

   For example,

        1.3.6.1.4.1.1466.1.2.3


4.1.3. Distinguished Name and Relative Distinguished Name

   An LDAPDN is defined to be the representation of a Distinguished Name
   (DN) after encoding according to the specification in [LDAPDN].

        LDAPDN ::= LDAPString
                   -- Constrained to <distinguishedName> [LDAPDN]

   A RelativeLDAPDN is defined to be the representation of a Relative
   Distinguished Name (RDN) after encoding according to the
   specification in [LDAPDN].

        RelativeLDAPDN ::= LDAPString
                           -- Constrained to <name-component> [LDAPDN]


4.1.4. Attribute Descriptions

   The definition and encoding rules for attribute descriptions are
   defined in Section 2.5 of [Models]. Briefly, an attribute description
   is an attribute type and zero or more options.

        AttributeDescription ::= LDAPString
                                -- Constrained to <attributedescription>
                                -- [Models]


4.1.5. Attribute Value

   A field of type AttributeValue is an OCTET STRING containing an
   encoded attribute value. The attribute value is encoded according to
   the LDAP-specific encoding definition of its corresponding syntax.
   The LDAP-specific encoding definitions for different syntaxes and
   attribute types may be found in other documents and in particular
   [Syntaxes].

        AttributeValue ::= OCTET STRING




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   Note that there is no defined limit on the size of this encoding;
   thus protocol values may include multi-megabyte attribute values
   (e.g. photographs).

   Attribute values may be defined which have arbitrary and non-
   printable syntax. Implementations MUST NOT display nor attempt to
   decode an attribute value if its syntax is not known. The
   implementation may attempt to discover the subschema of the source
   entry, and retrieve the descriptions of 'attributeTypes' from it
   [Models].

   Clients MUST only send attribute values in a request that are valid
   according to the syntax defined for the attributes.


4.1.6. Attribute Value Assertion

   The AttributeValueAssertion (AVA) type definition is similar to the
   one in the X.500 Directory standards. It contains an attribute
   description and a matching rule ([Models Section 4.1.3) assertion
   value suitable for that type. Elements of this type are typically
   used to assert that the value in assertionValue matches a value of an
   attribute.

        AttributeValueAssertion ::= SEQUENCE {
             attributeDesc   AttributeDescription,
             assertionValue  AssertionValue }

        AssertionValue ::= OCTET STRING

   The syntax of the AssertionValue depends on the context of the LDAP
   operation being performed. For example, the syntax of the EQUALITY
   matching rule for an attribute is used when performing a Compare
   operation. Often this is the same syntax used for values of the
   attribute type, but in some cases the assertion syntax differs from
   the value syntax. See objectIdentiferFirstComponentMatch in
   [Syntaxes] for an example.


4.1.7. Attribute and PartialAttribute

   Attributes and partial attributes consist of an attribute description
   and attribute values. A PartialAttribute allows zero values, while
   Attribute requires at least one value.

        PartialAttribute ::= SEQUENCE {
             type       AttributeDescription,
             vals       SET OF value AttributeValue }

        Attribute ::= PartialAttribute(WITH COMPONENTS {
             ...,
             vals (SIZE(1..MAX))})




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   No two attribute values may be equivalent as described by Section 2.3
   of [Models]. The set of attribute values is unordered.
   Implementations MUST NOT rely upon the ordering being repeatable.


4.1.8. Matching Rule Identifier

   Matching rules are defined in Section 4.1.3 of [Models]. A matching
   rule is identified in the protocol by the printable representation of
   either its <numericoid>, or one of its short name descriptors
   [Models], e.g. 'caseIgnoreMatch' or '2.5.13.2'.

        MatchingRuleId ::= LDAPString


4.1.9. Result Message

   The LDAPResult is the construct used in this protocol to return
   success or failure indications from servers to clients. To various
   requests, servers will return responses of LDAPResult or responses
   containing the components of LDAPResult to indicate the final status
   of a protocol operation request.

        LDAPResult ::= SEQUENCE {
             resultCode         ENUMERATED {
                  success                      (0),
                  operationsError              (1),
                  protocolError                (2),
                  timeLimitExceeded            (3),
                  sizeLimitExceeded            (4),
                  compareFalse                 (5),
                  compareTrue                  (6),
                  authMethodNotSupported       (7),
                  strongAuthRequired           (8),
                       -- 9 reserved --
                  referral                     (10),
                  adminLimitExceeded           (11),
                  unavailableCriticalExtension (12),
                  confidentialityRequired      (13),
                  saslBindInProgress           (14),
                  noSuchAttribute              (16),
                  undefinedAttributeType       (17),
                  inappropriateMatching        (18),
                  constraintViolation          (19),
                  attributeOrValueExists       (20),
                  invalidAttributeSyntax       (21),
                       -- 22-31 unused --
                  noSuchObject                 (32),
                  aliasProblem                 (33),
                  invalidDNSyntax              (34),
                       -- 35 reserved for undefined isLeaf --
                  aliasDereferencingProblem    (36),
                       -- 37-47 unused --
                  inappropriateAuthentication  (48),

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                  invalidCredentials           (49),
                  insufficientAccessRights     (50),
                  busy                         (51),
                  unavailable                  (52),
                  unwillingToPerform           (53),
                  loopDetect                   (54),
                       -- 55-63 unused --
                  namingViolation              (64),
                  objectClassViolation         (65),
                  notAllowedOnNonLeaf          (66),
                  notAllowedOnRDN              (67),
                  entryAlreadyExists           (68),
                  objectClassModsProhibited    (69),
                       -- 70 reserved for CLDAP --
                  affectsMultipleDSAs          (71),
                       -- 72-79 unused --
                  other                        (80),
                  ... },
             matchedDN          LDAPDN,
             diagnosticMessage  LDAPString,
             referral           [3] Referral OPTIONAL }

   The resultCode enumeration is extensible as defined in Section 3.6 of
   [LDAPIANA]. The meanings of the listed result codes are given in
   Appendix A. If a server detects multiple errors for an operation,
   only one result code is returned. The server should return the result
   code that best indicates the nature of the error encountered.

   The diagnosticMessage field of this construct may, at the server's
   option, be used to return a string containing a textual, human-
   readable (terminal control and page formatting characters should be
   avoided) diagnostic message. As this diagnostic message is not
   standardized, implementations MUST NOT rely on the values returned.
   If the server chooses not to return a textual diagnostic, the
   diagnosticMessage field MUST be empty.

   For certain result codes (typically, but not restricted to
   noSuchObject, aliasProblem, invalidDNSyntax and
   aliasDereferencingProblem), the matchedDN field is set to the name of
   the lowest entry (object or alias) in the Directory that was matched.
   If no aliases were dereferenced while attempting to locate the entry,
   this will be a truncated form of the name provided, or if aliases
   were dereferenced, of the resulting name, as defined in Section 12.5
   of [X.511]. Otherwise the matchedDN field is empty.


4.1.10. Referral

   The referral result code indicates that the contacted server cannot
   or will not perform the operation and that one or more other servers
   may be able to. Reasons for this include:

   - The target entry of the request is not held locally, but the
     server has knowledge of its possible existence elsewhere.

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   - The operation is restricted on this server -- perhaps due to a
     read-only copy of an entry to be modified.

   The referral field is present in an LDAPResult if the resultCode
   field value is referral, and absent with all other result codes. It
   contains one or more references to one or more servers or services
   that may be accessed via LDAP or other protocols. Referrals can be
   returned in response to any operation request (except unbind and
   abandon which do not have responses). At least one URI MUST be
   present in the Referral.

   During a search operation, after the baseObject is located, and
   entries are being evaluated, the referral is not returned. Instead,
   continuation references, described in Section 4.5.3, are returned
   when other servers would need to be contacted to complete the
   operation.

        Referral ::= SEQUENCE SIZE (1..MAX) OF uri URI

        URI ::= LDAPString     -- limited to characters permitted in
                               -- URIs

   If the client wishes to progress the operation, it MUST follow the
   referral by contacting one of the supported services. If multiple
   URIs are present, the client assumes that any supported URI may be
   used to progress the operation.

   Protocol peers that follow referrals MUST ensure that they do not
   loop between servers. They MUST NOT repeatedly contact the same
   server for the same request with the same target entry name, scope
   and filter. Some implementations use a counter that is incremented
   each time referral handling occurs for an operation, and these kinds
   of implementations MUST be able to handle at least ten nested
   referrals between the root and a leaf entry.

   A URI for a server implementing LDAP and accessible via [TCP]/[IP]
   (v4 or v6) is written as an LDAP URL according to [LDAPURL].

   When an LDAP URL is used, the following instructions are followed:

   - If an alias was dereferenced, the <dn> part of the URL MUST be
     present, with the new target object name. UTF-8 encoded characters
     appearing in the string representation of a DN or search filter
     may not be legal for URLs (e.g. spaces) and MUST be escaped using
     the % method in [URI].

   - It is RECOMMENDED that the <dn> part be present to avoid
     ambiguity.

   - If the <dn> part is present, the client MUST use this name in its
     next request to progress the operation, and if it is not present
     the client will use the same name as in the original request.


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   - Some servers (e.g. participating in distributed indexing) may
     provide a different filter in a URL of a referral for a search
     operation.

   - If the <filter> part of the LDAP URL is present, the client MUST
     use this filter in its next request to progress this search, and
     if it is not present the client MUST use the same filter as it
     used for that search.

   - For search, it is RECOMMENDED that the <scope> part be present to
     avoid ambiguity.

   - If the <scope> part is missing, the scope of the original search
     is used by the client to progress the operation.

   - Other aspects of the new request may be the same as or different
     from the request which generated the referral.

   Other kinds of URIs may be returned. The syntax and semantics of such
   URIs is left to future specifications. Clients may ignore URIs that
   they do not support.


4.1.11. Controls

   Controls provide a mechanism whereby the semantics and arguments of
   existing LDAP operations may be extended. One or more controls may be
   attached to a single LDAP message. A control only affects the
   semantics of the message it is attached to.

   Controls sent by clients are termed 'request controls' and those sent
   by servers are termed 'response controls'.

        Controls ::= SEQUENCE OF control Control

        Control ::= SEQUENCE {
             controlType             LDAPOID,
             criticality             BOOLEAN DEFAULT FALSE,
             controlValue            OCTET STRING OPTIONAL }

   The controlType field is the dotted-decimal representation of an
   OBJECT IDENTIFIER which uniquely identifies the control. This
   provides unambiguous naming of controls. Often, response control(s)
   solicited by a request control share controlType values with the
   request control.

   The criticality field only has meaning in controls attached to
   request messages (except unbindRequest). For controls attached to
   response messages and the unbindRequest, the criticality field SHOULD
   be FALSE, and MUST be ignored by the receiving protocol peer. A value
   of TRUE indicates that it is unacceptable to perform the operation
   without applying the semantics of the control and FALSE otherwise.
   Specifically, the criticality field is applied as follows:


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   - Regardless of the value of the criticality field, if the server
     recognizes the control type and it is appropriate for the
     operation, the server is to make use of the control when
     performing the operation.

   - If the server does not recognize the control type or it is not
     appropriate for the operation, and the criticality field is TRUE,
     the server MUST NOT perform the operation, and for operations that
     have a response message, MUST return unavailableCriticalExtension
     in the resultCode.

   - If the server does not recognize the control type or it is not
     appropriate for the operation, and the criticality field is FALSE,
     the server MUST ignore the control.

   The controlValue may contain information associated with the
   controlType. Its format is defined by the specification of the
   control. Implementations MUST be prepared to handle arbitrary
   contents of the controlValue octet string, including zero bytes. It
   is absent only if there is no value information which is associated
   with a control of its type. When a controlValue is defined in terms
   of ASN.1, and BER encoded according to Section 5.2, it also follows
   the extensibility rules in Section 4.

   Servers list the controlType of all request controls they recognize
   in the supportedControl attribute in the root DSE (Section 5.1 of
   [Models]).

   Controls SHOULD NOT be combined unless the semantics of the
   combination has been specified. The semantics of control
   combinations, if specified, are generally found in the control
   specification most recently published. When a combination of controls
   is encountered whose semantics are invalid, not specified (or not
   known), the message is considered to be not well-formed, thus the
   operation fails with protocolError. Additionally, unless order-
   dependent semantics are given in a specification, the order of a
   combination of controls in the SEQUENCE is ignored. Where the order
   is to be ignored but cannot be ignored by the server, the message is
   considered not well-formed and the operation fails with
   protocolError.

   This document does not specify any controls. Controls may be
   specified in other documents. Documents detailing control extensions
   are to provide for each control:

   - the OBJECT IDENTIFIER assigned to the control,

   - direction as to what value the sender should provide for the
     criticality field (note: the semantics of the criticality field
     are defined above should not be altered by the control's
     specification),

   - whether information is to be present in the controlValue field,
     and if so, the format of the controlValue contents,

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   - the semantics of the control, and

   - optionally, semantics regarding the combination of the control
     with other controls.


4.2. Bind Operation

   The function of the Bind Operation is to allow authentication
   information to be exchanged between the client and server. The Bind
   operation should be thought of as the "authenticate" operation.
   Operational, authentication, and security-related semantics of this
   operation are given in [AuthMeth].

   The Bind Request is defined as follows:

        BindRequest ::= [APPLICATION 0] SEQUENCE {
             version                 INTEGER (1 .. 127),
             name                    LDAPDN,
             authentication          AuthenticationChoice }

        AuthenticationChoice ::= CHOICE {
             simple                  [0] OCTET STRING,
                                     -- 1 and 2 reserved
             sasl                    [3] SaslCredentials,
             ... }

        SaslCredentials ::= SEQUENCE {
             mechanism               LDAPString,
             credentials             OCTET STRING OPTIONAL }

   Fields of the Bind Request are:

   - version: A version number indicating the version of the protocol
     to be used in this LDAP association. This document describes
     version 3 of the protocol. There is no version negotiation. The
     client sets this field to the version it desires. If the server
     does not support the specified version, it MUST respond with
     protocolError in the resultCode field of the BindResponse.

   - name: The name of the Directory object that the client wishes to
     bind as. This field may take on a null value (a zero length
     string) for the purposes of anonymous binds ([AuthMeth] Section
     5.1) or when using Simple Authentication and Security Layer [SASL]
     authentication ([AuthMeth] Section 3.3.2). Where the server
     attempts to locate the named object, it SHALL NOT perform alias
     dereferencing.

   - authentication: information used in authentication. This type is
     extensible as defined in Section 3.7 of [LDAPIANA]. Servers that
     do not support a choice supplied by a client return
     authMethodNotSupported in the resultCode field of the
     BindResponse.

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     Textual passwords (consisting of a character sequence with a known
     character set and encoding) transferred to the server using the
     simple AuthenticationChoice SHALL be transferred as [UTF-8]
     encoded [Unicode]. Prior to transfer, clients SHOULD prepare text
     passwords by applying the [SASLprep] profile of the [Stringprep]
     algorithm. Passwords consisting of other data (such as random
     octets) MUST NOT be altered. The determination of whether a
     password is textual is a local client matter.

   Authorization is the decision of which access an operation has to the
   directory. Among other things, the process of authorization takes as
   input authentication information obtained during the bind operation
   and/or other acts of authentication (such as lower layer security
   services).


4.2.1. Processing of the Bind Request

   Before processing a BindRequest, all uncompleted operations MUST
   either complete or be abandoned. The server may either wait for the
   uncompleted operations to complete, or abandon them. The server then
   proceeds to authenticate the client in either a single-step, or
   multi-step bind process. Each step requires the server to return a
   BindResponse to indicate the status of authentication.

   After sending a BindRequest, clients MUST NOT send further LDAP PDUs
   until receiving the BindResponse. Similarly, servers SHOULD NOT
   process or respond to requests received while processing a
   BindRequest.

   If the client did not bind before sending a request and receives an
   operationsError to that request, it may then send a Bind Request. If
   this also fails or the client chooses not to bind on the existing
   LDAP exchange, it may close the connection, reopen it and begin again
   by first sending a PDU with a Bind Request. This will aid in
   interoperating with servers implementing other versions of LDAP.

   Clients may send multiple Bind Requests on an LDAP exchange to change
   the authentication and/or security associations or to complete a
   multi-stage bind process. Authentication from earlier binds is
   subsequently ignored.

   For some SASL authentication mechanisms, it may be necessary for the
   client to invoke the BindRequest multiple times ([AuthMeth] Section
   8.2). Clients MUST NOT invoke operations between two Bind Requests
   made as part of a multi-stage bind.

   A client may abort a SASL bind negotiation by sending a BindRequest
   with a different value in the mechanism field of SaslCredentials, or
   an AuthenticationChoice other than sasl.

   If the client sends a BindRequest with the sasl mechanism field as an
   empty string, the server MUST return a BindResponse with

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   authMethodNotSupported as the resultCode. This will allow clients to
   abort a negotiation if it wishes to try again with the same SASL
   mechanism.


4.2.2. Bind Response

   The Bind Response is defined as follows.

        BindResponse ::= [APPLICATION 1] SEQUENCE {
             COMPONENTS OF LDAPResult,
             serverSaslCreds    [7] OCTET STRING OPTIONAL }

   BindResponse consists simply of an indication from the server of the
   status of the client's request for authentication.

   A successful bind operation is indicated by a BindResponse with a
   resultCode set to success. Otherwise, an appropriate result code is
   set in the BindResponse. For bind, the protocolError result code may
   be used to indicate that the version number supplied by the client is
   unsupported.

   If the client receives a BindResponse where the resultCode field is
   protocolError, it is to assume that the server does not support this
   version of LDAP. While the client may be able proceed with another
   version of this protocol (this may or may not require closing and re-
   establishing the connection), how to proceed with another version of
   this protocol is beyond the scope of this document. Clients which are
   unable or unwilling to proceed SHOULD close the connection.

   The serverSaslCreds field is used as part of a SASL-defined bind
   mechanism to allow the client to authenticate the server to which it
   is communicating, or to perform "challenge-response" authentication.
   If the client bound with the simple choice, or the SASL mechanism
   does not require the server to return information to the client, then
   this field SHALL NOT be included in the BindResponse.


4.3. Unbind Operation

   The function of the Unbind Operation is to terminate an LDAP
   association and close the connection. The Unbind operation is not the
   antithesis of the Bind operation as the name implies. The naming of
   these operations is historical. The Unbind operation should be
   thought of as the "quit" operation.

   The Unbind Operation is defined as follows:

        UnbindRequest ::= [APPLICATION 2] NULL

   The Unbind Operation has no response defined. Upon transmission of
   the UnbindRequest, each protocol peer is to consider the LDAP
   association terminated, MUST cease transmission of messages to the



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   other peer, and MUST close the connection. Uncompleted operations are
   handled as specified in Section 5.1.


4.4. Unsolicited Notification

   An unsolicited notification is an LDAPMessage sent from the server to
   the client which is not in response to any LDAPMessage received by
   the server. It is used to signal an extraordinary condition in the
   server or in the LDAP exchange or connection between the client and
   the server. The notification is of an advisory nature, and the server
   will not expect any response to be returned from the client.

   The unsolicited notification is structured as an LDAPMessage in which
   the messageID is zero and protocolOp is of the extendedResp form (See
   Section 4.12). The responseName field of the ExtendedResponse always
   contains an LDAPOID which is unique for this notification.

   One unsolicited notification (Notice of Disconnection) is defined in
   this document. The specification of an unsolicited notification
   consists of:

   - the OBJECT IDENTIFIER assigned to the notification (to be
     specified in the responseName,

   - the format of the contents (if any) of the responseValue,

   - the circumstances which will cause the notification to be
     returned, and

   - the semantics of the operation.


4.4.1. Notice of Disconnection

   This notification may be used by the server to advise the client that
   the server is about to close the connection due to an error
   condition. This notification is intended to assist clients in
   distinguishing between an error condition and a transient network
   failure. Note that this notification is not a response to an unbind
   requested by the client. Uncompletetd operations are handled as
   specified in Section 5.1.

   The responseName is 1.3.6.1.4.1.1466.20036, the response field is
   absent, and the resultCode is used to indicate the reason for the
   disconnection.

   The following result codes have these meanings when used in this
   notification:

   - protocolError: The server has received data from the client in
     which the LDAPMessage structure could not be parsed.




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   - strongAuthRequired: The server has detected that an established
     security association between the client and server has
     unexpectedly failed or been compromised, or that the server now
     requires the client to authenticate using a strong(er) mechanism.

   - unavailable: This server will stop accepting new connections and
     operations on all existing LDAP exchanges, and be unavailable for
     an extended period of time. The client may make use of an
     alternative server.

   Upon transmission of the Notice of Disconnection, the server is to
   consider the LDAP association terminated, MUST cease transmission of
   messages to the client, and MUST close the connection.


4.5. Search Operation

   The Search Operation is used to request a server to return, subject
   to access controls and other restrictions, a set of entries matching
   a complex search criterion. This can be used to read attributes from
   a single entry, from entries immediately subordinate to a particular
   entry, or a whole subtree of entries.


4.5.1. Search Request

   The Search Request is defined as follows:

        SearchRequest ::= [APPLICATION 3] SEQUENCE {
             baseObject      LDAPDN,
             scope           ENUMERATED {
                  baseObject              (0),
                  singleLevel             (1),
                  wholeSubtree            (2) },
             derefAliases    ENUMERATED {
                  neverDerefAliases       (0),
                  derefInSearching        (1),
                  derefFindingBaseObj     (2),
                  derefAlways             (3) },
             sizeLimit       INTEGER (0 .. maxInt),
             timeLimit       INTEGER (0 .. maxInt),
             typesOnly       BOOLEAN,
             filter          Filter,
             attributes      AttributeSelection }

        AttributeSelection ::= SEQUENCE OF selector LDAPString
                        -- The LDAPString is constrained to
                        -- <attributeSelector> below

        Filter ::= CHOICE {
             and             [0] SET SIZE (1..MAX) OF filter Filter,
             or              [1] SET SIZE (1..MAX) OF filter Filter,
             not             [2] Filter,
             equalityMatch   [3] AttributeValueAssertion,

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             substrings      [4] SubstringFilter,
             greaterOrEqual  [5] AttributeValueAssertion,
             lessOrEqual     [6] AttributeValueAssertion,
             present         [7] AttributeDescription,
             approxMatch     [8] AttributeValueAssertion,
             extensibleMatch [9] MatchingRuleAssertion }

        SubstringFilter ::= SEQUENCE {
             type           AttributeDescription,
             -- initial and final can occur at most once
             substrings     SEQUENCE SIZE (1..MAX) OF substring CHOICE {
                  initial [0] AssertionValue,
                  any     [1] AssertionValue,
                  final   [2] AssertionValue } }

        MatchingRuleAssertion ::= SEQUENCE {
             matchingRule    [1] MatchingRuleId OPTIONAL,
             type            [2] AttributeDescription OPTIONAL,
             matchValue      [3] AssertionValue,
             dnAttributes    [4] BOOLEAN DEFAULT FALSE }

   Fields of the Search Request are:

   - baseObject: The name of the base object entry relative to which
     the search is to be performed.

   - scope: Specifies the scope of the search to be performed. The
     semantics (as described in [X.511]) of the possible values of this
     field are:

        baseObject:  The scope is constrained to the entry named by
        baseObject.

        singleLevel: The scope is constrained to the immediate
        subordinates of the entry named by baseObject.

        wholeSubtree: the scope is constrained to the entry named by
        the baseObject, and all its subordinates.


   - derefAliases: An indicator as to how alias entries (as defined in
     [Models]) are to be handled in searching. The semantics of the
     possible values of this field are:

        neverDerefAliases: Do not dereference aliases in searching or
        in locating the base object of the search.

        derefInSearching: While searching, dereference any alias entry
        subordinate to the base object which is also in the search
        scope. The filter is applied to the dereferenced object(s). If
        the search scope is wholeSubtree, the search continues in the
        subtree of any dereferenced object. Aliases in that subtree are
        also dereferenced. Servers SHOULD eliminate duplicate entries
        that arise due to alias dereferencing while searching.

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        derefFindingBaseObj: Dereference aliases in locating the base
        object of the search, but not when searching subordinates of
        the base object.

        derefAlways: Dereference aliases both in searching and in
        locating the base object of the search.
     Servers MUST detect looping while dereferencing aliases in order
     to prevent denial of service attacks of this nature.

   - sizeLimit: A size limit that restricts the maximum number of
     entries to be returned as a result of the search. A value of zero
     in this field indicates that no client-requested size limit
     restrictions are in effect for the search. Servers may also
     enforce a maximum number of entries to return.

   - timeLimit: A time limit that restricts the maximum time (in
     seconds) allowed for a search. A value of zero in this field
     indicates that no client-requested time limit restrictions are in
     effect for the search. Servers may also enforce a maximum time
     limit for the search.

   - typesOnly: An indicator as to whether search results are to
     contain both attribute descriptions and values, or just attribute
     descriptions. Setting this field to TRUE causes only attribute
     descriptions (no values) to be returned. Setting this field to
     FALSE causes both attribute descriptions and values to be
     returned.

   - filter: A filter that defines the conditions that must be
     fulfilled in order for the search to match a given entry.

     The 'and', 'or' and 'not' choices can be used to form combinations
     of filters. At least one filter element MUST be present in an
     'and' or 'or' choice. The others match against individual
     attribute values of entries in the scope of the search.
     (Implementor's note: the 'not' filter is an example of a tagged
     choice in an implicitly-tagged module. In BER this is treated as
     if the tag was explicit.)

     A server MUST evaluate filters according to the three-valued logic
     of X.511 (1993) Section 7.8.1. In summary, a filter is evaluated
     to either "TRUE", "FALSE" or "Undefined". If the filter evaluates
     to TRUE for a particular entry, then the attributes of that entry
     are returned as part of the search result (subject to any
     applicable access control restrictions). If the filter evaluates
     to FALSE or Undefined, then the entry is ignored for the search.

     A filter of the "and" choice is TRUE if all the filters in the SET
     OF evaluate to TRUE, FALSE if at least one filter is FALSE, and
     otherwise Undefined. A filter of the "or" choice is FALSE if all
     of the filters in the SET OF evaluate to FALSE, TRUE if at least
     one filter is TRUE, and Undefined otherwise. A filter of the 'not'
     choice is TRUE if the filter being negated is FALSE, FALSE if it

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     is TRUE, and Undefined if it is Undefined.

     The present match evaluates to TRUE where there is an attribute or
     subtype of the specified attribute description present in an
     entry, and FALSE otherwise (including a presence test with an
     unrecognized attribute description.)

     The matching rule for equalityMatch filter items is defined by the
     EQUALITY matching rule for the attribute type.

     There SHALL be at most one 'initial', and at most one 'final' in
     the 'substrings' of a SubstringFilter. If 'initial' is present, it
     SHALL be the first element of 'substrings'. If 'final' is present,
     it SHALL be the last element of 'substrings'.
     The matching rule for AssertionValues in a substrings filter item
     is defined by the SUBSTR matching rule for the attribute type.
     Note that the AssertionValue in a substrings filter item conforms
     to the assertion syntax of the EQUALITY matching rule for the
     attribute type rather than the assertion syntax of the SUBSTR
     matching rule for the attribute type. Conceptually, the entire
     SubstringFilter is converted into an assertion value of the
     substrings matching rule prior to applying the rule.

     The matching rule for the greaterOrEqual filter item is defined by
     the ORDERING and EQUALITY matching rules for the attribute type.

     The matching rule for the lessOrEqual filter item is defined by
     the ORDERING matching rule for the attribute type.

     An approxMatch filter item evaluates to TRUE when there is a value
     of the attribute or subtype for which some locally-defined
     approximate matching algorithm (e.g. spelling variations, phonetic
     match, etc.) returns TRUE. If an item matches for equality, it
     also satisfies an approximate match. If approximate matching is
     not supported, this filter item should be treated as an
     equalityMatch.

     An extensibleMatch filter item is evaluated as follows:

        If the matchingRule field is absent, the type field MUST be
        present, and an equality match is performed for that type.

        If the type field is absent and the matchingRule is present, the
        matchValue is compared against all attributes in an entry which
        support that matchingRule. The matchingRule determines the
        syntax for the assertion value. The filter item evaluates to
        TRUE if it matches with at least one attribute in the entry,
        FALSE if it does not match any attribute in the entry, and
        Undefined if the matchingRule is not recognized or the
        assertionValue is invalid.

        If the type field is present and the matchingRule is present,
        the matchValue is compared against entry attributes of the
        specified type. In this case, the matchingRule MUST be one

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        suitable for use with the specified type (see [Syntaxes]),
        otherwise the filter item is Undefined.

        If the dnAttributes field is set to TRUE, the match is
        additionally applied against all the AttributeValueAssertions in
        an entry's distinguished name, and evaluates to TRUE if there is
        at least one attribute in the distinguished name for which the
        filter item evaluates to TRUE. The dnAttributes field is present
        to alleviate the need for multiple versions of generic matching
        rules (such as word matching), where one applies to entries and
        another applies to entries and dn attributes as well.

     A filter item evaluates to Undefined when the server would not be
     able to determine whether the assertion value matches an entry. If
     an attribute description in an equalityMatch, substrings,
     greaterOrEqual, lessOrEqual, approxMatch or extensibleMatch filter
     is not recognized by the server, a matching rule id in the
     extensibleMatch is not recognized by the server, the assertion
     value is invalid, or the type of filtering requested is not
     implemented, then the filter is Undefined. Thus for example if a
     server did not recognize the attribute type shoeSize, a filter of
     (shoeSize=*) would evaluate to FALSE, and the filters
     (shoeSize=12), (shoeSize>=12) and (shoeSize<=12) would evaluate to
     Undefined.

     Servers MUST NOT return errors if attribute descriptions or
     matching rule ids are not recognized, assertion values are
     invalid, or the assertion syntax is not supported. More details of
     filter processing are given in Section 7.8 of [X.511].

   - attributes: A selection list of the attributes to be returned from
     each entry which matches the search filter. LDAPString values of
     this field are constrained to the following Augmented Backus-Naur
     Form ([ABNF]):

     attributeSelector = attributedescription / selectorpecial

     selectorspecial = noattrs / alluserattrs

     noattrs = %x31.2E.31 ; "1.1"

     alluserattrs = %x2A ; asterisk ("*")

     The <attributedescription> production is defined in Section 2.5 of
     [Models].

     There are three special cases which may exist in the attribute
     selection:

     - an empty list with no attributes,

     - a list containing "*" (with zero or more attribute
        descriptions), and


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     - a list containing only "1.1".

     An empty list requests the return of all user attributes.

     A list containing "*" requests all user attributes in addition to
     other listed (operational) attributes.

     A list containing only the OID "1.1" indicates that no values are
     to be returned. If "1.1" is provided with other values, the "1.1"
     value is ignored. This OID was chosen because it does not (and can
     not) correspond to any attribute in use.

     Client implementors should note that even if all user attributes
     are requested, some attributes and/or attribute values of the
     entry may not be included in search results due to access controls
     or other restrictions. Furthermore, servers will not return
     operational attributes, such as objectClasses or attributeTypes,
     unless they are listed by name. Operational attributes are
     described in [Models].

     Attributes are returned at most once in an entry. If an attribute
     description is named more than once in the list, the subsequent
     names are ignored. If an attribute description in the list is not
     recognized, it is ignored by the server.

   Note that an X.500 "list"-like operation can be emulated by the
   client requesting a one-level LDAP search operation with a filter
   checking for the presence of the 'objectClass' attribute, and that an
   X.500 "read"-like operation can be emulated by a base object LDAP
   search operation with the same filter. A server which provides a
   gateway to X.500 is not required to use the Read or List operations,
   although it may choose to do so, and if it does, it must provide the
   same semantics as the X.500 search operation.


4.5.2. Search Result

   The results of the search operation are returned as zero or more
   searchResultEntry messages, zero or more SearchResultReference
   messages, followed by a single searchResultDone message.

        SearchResultEntry ::= [APPLICATION 4] SEQUENCE {
             objectName      LDAPDN,
             attributes      PartialAttributeList }

        PartialAttributeList ::= SEQUENCE OF
                             partialAttribute PartialAttribute
        -- Note that the PartialAttributeList may hold zero elements.
        -- This may happen when none of the attributes of an entry
        -- were requested, or could be returned.
        -- Note also that the partialAttribute vals set may hold zero
        -- elements. This may happen when typesOnly is requested, access
        -- controls prevent the return of values, or other reasons.


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        SearchResultReference ::= [APPLICATION 19] SEQUENCE
                                  SIZE (1..MAX) OF uri URI

        SearchResultDone ::= [APPLICATION 5] LDAPResult

   Each SearchResultEntry represents an entry found during the search.
   Each SearchResultReference represents an area not yet explored during
   the search. The SearchResultEntry and SearchResultReference PDUs may
   come in any order. Following all the SearchResultReference and
   SearchResultEntry responses, the server returns a SearchResultDone
   response, which contains an indication of success, or detailing any
   errors that have occurred.

   Each entry returned in a SearchResultEntry will contain all
   appropriate attributes as specified in the attributes field of the
   Search Request. Return of attributes is subject to access control and
   other administrative policy.

   Some attributes may be constructed by the server and appear in a
   SearchResultEntry attribute list, although they are not stored
   attributes of an entry. Clients SHOULD NOT assume that all attributes
   can be modified, even if permitted by access control.

   If the server's schema defines short names [Models] for an attribute
   type then the server SHOULD use one of those names in attribute
   descriptions for that attribute type (in preference to using the
   <numericoid> [Models] format of the attribute type's object
   identifier). The server SHOULD NOT use the short name if that name is
   known by the server to be ambiguous, or otherwise likely to cause
   interoperability problems.


4.5.3. Continuation References in the Search Result

   If the server was able to locate the entry referred to by the
   baseObject but was unable to search one or more non-local entries,
   the server may return one or more SearchResultReference entries, each
   containing a reference to another set of servers for continuing the
   operation. A server MUST NOT return any SearchResultReference if it
   has not located the baseObject and thus has not searched any entries;
   in this case it would return a SearchResultDone containing either a
   referral or noSuchObject result code (depending on the server's
   knowledge of the entry named in the baseObject).

   If a server holds a copy or partial copy of the subordinate naming
   context [Section 5 of Models], it may use the search filter to
   determine whether or not to return a SearchResultReference response.
   Otherwise SearchResultReference responses are always returned when in
   scope.

   The SearchResultReference is of the same data type as the Referral.

   A URI for a server implementing LDAP and accessible via [TCP]/[IP]
   (v4 or v6) is written as an LDAP URL according to [LDAPURL].

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   In order to complete the search, the client issues a new search
   operation for each SearchResultReference that is returned. Note that
   the abandon operation described in Section 4.11 applies only to a
   particular operation sent on an association between a client and
   server. The client must abandon subsequent search operations it
   wishes to individually.

   Clients that follow search continuation references MUST ensure that
   they do not loop between servers. They MUST NOT repeatedly contact
   the same server for the same request with the same target entry name,
   scope and filter. Some clients use a counter that is incremented each
   time search result reference handling occurs for an operation, and
   these kinds of clients MUST be able to handle at least ten nested
   search result references between the root and a leaf entry.

   When an LDAP URL is used, the following instructions are followed:

   - The <dn> part of the URL MUST be present, with the new target
     object name. The client MUST use this name when following the
     reference. UTF-8 encoded characters appearing in the string
     representation of a DN or search filter may not be legal for URLs
     (e.g. spaces) and MUST be escaped using the % method in [URI].

   - Some servers (e.g. participating in distributed indexing) may
     provide a different filter in a URL of a SearchResultReference.

   - If the <filter> part of the URL is present, the client MUST use
     this filter in its next request to progress this search, and if it
     is not present the client MUST use the same filter as it used for
     that search.

   - If the originating search scope was singleLevel, the <scope> part
     of the URL will be "base".

   - it is RECOMMENDED that the <scope> part be present to avoid
     ambiguity.

   - Other aspects of the new search request may be the same as or
     different from the search request which generated the
     SearchResultReference.

   - The name of an unexplored subtree in a SearchResultReference need
     not be subordinate to the base object.

   Other kinds of URIs may be returned. The syntax and semantics of such
   URIs is left to future specifications. Clients may ignore URIs that
   they do not support.


4.5.3.1. Examples

   For example, suppose the contacted server (hosta) holds the entry
   <DC=Example,DC=NET> and the entry <CN=Manager,DC=Example,DC=NET>. It

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   knows that either LDAP-capable servers (hostb) or (hostc) hold
   <OU=People,DC=Example,DC=NET> (one is the master and the other server
   a shadow), and that LDAP-capable server (hostd) holds the subtree
   <OU=Roles,DC=Example,DC=NET>. If a wholeSubtree search of
   <DC=Example,DC=NET> is requested to the contacted server, it may
   return the following:

     SearchResultEntry for DC=Example,DC=NET
     SearchResultEntry for CN=Manager,DC=Example,DC=NET
     SearchResultReference {
       ldap://hostb/OU=People,DC=Example,DC=NET??sub
       ldap://hostc/OU=People,DC=Example,DC=NET??sub }
     SearchResultReference {
       ldap://hostd/OU=Roles,DC=Example,DC=NET??sub }
     SearchResultDone (success)

   Client implementors should note that when following a
   SearchResultReference, additional SearchResultReference may be
   generated. Continuing the example, if the client contacted the server
   (hostb) and issued the search for the subtree
   <OU=People,DC=Example,DC=NET>, the server might respond as follows:

     SearchResultEntry for OU=People,DC=Example,DC=NET
     SearchResultReference {
       ldap://hoste/OU=Managers,OU=People,DC=Example,DC=NET??sub }
     SearchResultReference {
       ldap://hostf/OU=Consultants,OU=People,DC=Example,DC=NET??sub }
     SearchResultDone (success)

   Similarly, if a singleLevel search of <DC=Example,DC=NET> is
   requested to the contacted server, it may return the following:

     SearchResultEntry for CN=Manager,DC=Example,DC=NET
     SearchResultReference {
       ldap://hostb/OU=People,DC=Example,DC=NET??base
       ldap://hostc/OU=People,DC=Example,DC=NET??base }
     SearchResultReference {
       ldap://hostd/OU=Roles,DC=Example,DC=NET??base }
     SearchResultDone (success)

   If the contacted server does not hold the base object for the search,
   but has knowledge of its possible location, then it may return a
   referral to the client. In this case, if the client requests a
   subtree search of <DC=Example,DC=ORG> to hosta, the server returns a
   SearchResultDone containing a referral.

     SearchResultDone (referral) {
       ldap://hostg/DC=Example,DC=ORG??sub }


4.6. Modify Operation





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   The Modify Operation allows a client to request that a modification
   of an entry be performed on its behalf by a server. The Modify
   Request is defined as follows:

        ModifyRequest ::= [APPLICATION 6] SEQUENCE {
             object          LDAPDN,
             changes         SEQUENCE OF change SEQUENCE {
                  operation       ENUMERATED {
                       add     (0),
                       delete  (1),
                       replace (2) },
                  modification    PartialAttribute } }

   Fields of the Modify Request are:

   - object: The name of the object to be modified. The value of this
     field contains the DN of the entry to be modified. The server
     SHALL NOT perform any alias dereferencing in determining the
     object to be modified.

   - changes: A list of modifications to be performed on the entry. The
     entire list of modifications MUST be performed in the order they
     are listed as a single atomic operation. While individual
     modifications may violate certain aspects of the directory schema
     (such as the object class definition and DIT content rule), the
     resulting entry after the entire list of modifications is
     performed MUST conform to the requirements of the directory model
     and controlling schema [Models].

     -  operation: Used to specify the type of modification being
        performed. Each operation type acts on the following
        modification. The values of this field have the following
        semantics respectively:

           add: add values listed to the modification attribute,
           creating the attribute if necessary;

           delete: delete values listed from the modification attribute,
           removing the entire attribute if no values are listed, or if
           all current values of the attribute are listed for deletion;

           replace: replace all existing values of the modification
           attribute with the new values listed, creating the attribute
           if it did not already exist. A replace with no value will
           delete the entire attribute if it exists, and is ignored if
           the attribute does not exist.

     -  modification: A PartialAttribute (which may have an empty SET
        of vals) used to hold the attribute type or attribute type and
        values being modified.

   Upon receipt of a Modify Request, the server attempts to perform the
   necessary modifications to the DIT and returns the result in a Modify
   Response, defined as follows:

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        ModifyResponse ::= [APPLICATION 7] LDAPResult

   The server will return to the client a single Modify Response
   indicating either the successful completion of the DIT modification,
   or the reason that the modification failed. Due to the requirement
   for atomicity in applying the list of modifications in the Modify
   Request, the client may expect that no modifications of the DIT have
   been performed if the Modify Response received indicates any sort of
   error, and that all requested modifications have been performed if
   the Modify Response indicates successful completion of the Modify
   Operation. If the association changes or the connection fails,
   whether the modification occurred or not is indeterminate.

   The Modify Operation cannot be used to remove from an entry any of
   its distinguished values, i.e. those values which form the entry's
   relative distinguished name. An attempt to do so will result in the
   server returning the notAllowedOnRDN result code. The Modify DN
   Operation described in Section 4.9 is used to rename an entry.

   Note that due to the simplifications made in LDAP, there is not a
   direct mapping of the changes in an LDAP ModifyRequest onto the
   changes of a DAP ModifyEntry operation, and different implementations
   of LDAP-DAP gateways may use different means of representing the
   change. If successful, the final effect of the operations on the
   entry MUST be identical.


4.7. Add Operation

   The Add Operation allows a client to request the addition of an entry
   into the Directory. The Add Request is defined as follows:

        AddRequest ::= [APPLICATION 8] SEQUENCE {
             entry           LDAPDN,
             attributes      AttributeList }

        AttributeList ::= SEQUENCE OF attribute Attribute

   Fields of the Add Request are:

   - entry: the name of the entry to be added. The server SHALL NOT
     dereference any aliases in locating the entry to be added.

   - attributes: the list of attributes that, along with those from the
     RDN, make up the content of the entry being added. Clients MAY or
     MAY NOT include the RDN attribute in this list. Clients MUST
     include the 'objectClass' attribute, and values of any mandatory
     attributes of the listed object classes. Clients MUST NOT supply
     NO-USER-MODIFICATION attributes such as the createTimestamp or
     creatorsName attributes, since the server maintains these
     automatically.




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   The entry named in the entry field of the AddRequest MUST NOT exist
   for the AddRequest to succeed. The immediate superior (parent) of an
   object or alias entry to be added MUST exist. For example, if the
   client attempted to add <CN=JS,DC=Example,DC=NET>, the
   <DC=Example,DC=NET> entry did not exist, and the <DC=NET> entry did
   exist, then the server would return the noSuchObject result code with
   the matchedDN field containing <DC=NET>.

   Server implementations SHOULD NOT restrict where entries can be
   located in the Directory unless DIT structure rules are in place.
   Some servers allow the administrator to restrict the classes of
   entries which can be added to the Directory.

   Upon receipt of an Add Request, a server will attempt to add the
   requested entry. The result of the add attempt will be returned to
   the client in the Add Response, defined as follows:

        AddResponse ::= [APPLICATION 9] LDAPResult

   A response of success indicates that the new entry has been added to
   the Directory.


4.8. Delete Operation

   The Delete Operation allows a client to request the removal of an
   entry from the Directory. The Delete Request is defined as follows:

        DelRequest ::= [APPLICATION 10] LDAPDN

   The Delete Request consists of the name of the entry to be deleted.
   The server SHALL NOT dereference aliases while resolving the name of
   the target entry to be removed.

   Only leaf entries (those with no subordinate entries) can be deleted
   with this operation.

   Upon receipt of a Delete Request, a server will attempt to perform
   the entry removal requested and return the result in the Delete
   Response defined as follows:

        DelResponse ::= [APPLICATION 11] LDAPResult


4.9. Modify DN Operation

   The Modify DN Operation allows a client to change the Relative
   Distinguished Name (RDN) of an entry in the Directory, and/or to move
   a subtree of entries to a new location in the Directory. The Modify
   DN Request is defined as follows:

        ModifyDNRequest ::= [APPLICATION 12] SEQUENCE {
             entry           LDAPDN,
             newrdn          RelativeLDAPDN,

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             deleteoldrdn    BOOLEAN,
             newSuperior     [0] LDAPDN OPTIONAL }

   Fields of the Modify DN Request are:

   - entry: the name of the entry to be changed. This entry may or may
     not have subordinate entries.

   - newrdn: the new RDN of the entry. If the operation moves the entry
     to a new superior without changing its RDN, the value of the old
     RDN is supplied for this parameter.
     Attribute values of the new RDN not matching any attribute value
     of the entry are added to the entry and an appropriate error is
     returned if this fails.

   - deleteoldrdn: a boolean field that controls whether the old RDN
     attribute values are to be retained as attributes of the entry, or
     deleted from the entry.

   - newSuperior: if present, this is the name of an existing object
     entry which becomes the immediate superior (parent) of the
     existing entry.

   The server SHALL NOT dereference any aliases in locating the objects
   named in entry or newSuperior.

   Upon receipt of a ModifyDNRequest, a server will attempt to perform
   the name change and return the result in the Modify DN Response,
   defined as follows:

        ModifyDNResponse ::= [APPLICATION 13] LDAPResult

   For example, if the entry named in the entry field was <cn=John
   Smith,c=US>, the newrdn field was <cn=John Cougar Smith>, and the
   newSuperior field was absent, then this operation would attempt to
   rename the entry to be <cn=John Cougar Smith,c=US>. If there was
   already an entry with that name, the operation would fail with the
   entryAlreadyExists result code.

   The object named in newSuperior MUST exist. For example, if the
   client attempted to add <CN=JS,DC=Example,DC=NET>, the
   <DC=Example,DC=NET> entry did not exist, and the <DC=NET> entry did
   exist, then the server would return the noSuchObject result code with
   the matchedDN field containing <DC=NET>.

   If the deleteoldrdn field is TRUE, the attribute values forming the
   old RDN but not the new RDN are deleted from the entry. If the
   deleteoldrdn field is FALSE, the attribute values forming the old RDN
   will be retained as non-distinguished attribute values of the entry.
   The server MUST fail the operation and return an error in the result
   code if the setting of the deleteoldrdn field would cause a schema
   inconsistency in the entry.




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   Note that X.500 restricts the ModifyDN operation to only affect
   entries that are contained within a single server. If the LDAP server
   is mapped onto DAP, then this restriction will apply, and the
   affectsMultipleDSAs result code will be returned if this error
   occurred. In general, clients MUST NOT expect to be able to perform
   arbitrary movements of entries and subtrees between servers or
   between naming contexts.


4.10. Compare Operation

   The Compare Operation allows a client to compare an assertion value
   with the values of a particular attribute in a particular entry in
   the Directory. The Compare Request is defined as follows:

        CompareRequest ::= [APPLICATION 14] SEQUENCE {
             entry           LDAPDN,
             ava             AttributeValueAssertion }

   Fields of the Compare Request are:

   - entry: the name of the entry to be compared. The server SHALL NOT
     dereference any aliases in locating the entry to be compared.

   - ava: holds the attribute value assertion to be compared.

   Upon receipt of a Compare Request, a server will attempt to perform
   the requested comparison and return the result in the Compare
   Response, defined as follows:

        CompareResponse ::= [APPLICATION 15] LDAPResult

   The resultCode field is set to compareTrue, compareFalse, or an
   appropriate error. compareTrue indicates that the assertion value in
   the ava field matches a value of the attribute or subtype according
   to the attribute's EQUALITY matching rule. compareFalse indicates
   that the assertion value in the ava field and the values of the
   attribute or subtype did not match. Other result codes indicate
   either that the result of the comparison was Undefined (Section
   4.5.1), or that some error occurred.

   Note that some directory systems may establish access controls which
   permit the values of certain attributes (such as userPassword) to be
   compared but not interrogated by other means.


4.11. Abandon Operation

   The function of the Abandon Operation is to allow a client to request
   that the server abandon an uncompleted operation. The Abandon Request
   is defined as follows:

        AbandonRequest ::= [APPLICATION 16] MessageID


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   The MessageID is that of an operation which was requested earlier in
   this LDAP association. The abandon request itself has its own message
   id. This is distinct from the id of the earlier operation being
   abandoned.

   There is no response defined in the Abandon operation. Upon receipt
   of an AbandonRequest, the server MAY abandon the operation identified
   by the MessageID. Since the client cannot tell the difference between
   a successfully abandoned operation and an uncompleted operation, the
   application of the Abandon operation is limited to uses where the
   client does not require an indication of its outcome.

   Abandon, Bind, Unbind, and StartTLS operations cannot be abandoned.

   In the event that a server receives an Abandon Request on a Search
   Operation in the midst of transmitting responses to the search, that
   server MUST cease transmitting entry responses to the abandoned
   request immediately, and MUST NOT send the SearchResponseDone. Of
   course, the server MUST ensure that only properly encoded LDAPMessage
   PDUs are transmitted.

   The ability to abandon other (particularly update) operations is at
   the discretion of the server.

   Clients should not send abandon requests for the same operation
   multiple times, and MUST also be prepared to receive results from
   operations it has abandoned (since these may have been in transit
   when the abandon was requested, or are not able to be abandoned).

   Servers MUST discard abandon requests for message IDs they do not
   recognize, for operations which cannot be abandoned, and for
   operations which have already been abandoned.


4.12. Extended Operation

   The extended operation allows additional operations to be defined for
   services not already available in the protocol. For example, to add
   operations to install transport layer security (see Section 4.14).

   The extended operation allows clients to make requests and receive
   responses with predefined syntaxes and semantics. These may be
   defined in RFCs or be private to particular implementations.

   Each extended operation consists of an extended request and an
   extended response.

        ExtendedRequest ::= [APPLICATION 23] SEQUENCE {
             requestName      [0] LDAPOID,
             requestValue     [1] OCTET STRING OPTIONAL }

   The requestName is a dotted-decimal representation of the unique
   OBJECT IDENTIFIER corresponding to the request. The requestValue is



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   information in a form defined by that request, encapsulated inside an
   OCTET STRING.

   The server will respond to this with an LDAPMessage containing an
   ExtendedResponse.

        ExtendedResponse ::= [APPLICATION 24] SEQUENCE {
             COMPONENTS OF LDAPResult,
             responseName     [10] LDAPOID OPTIONAL,
             responseValue    [11] OCTET STRING OPTIONAL }

   The responseName is typically not required to be present as the
   syntax and semantics of the response (including the format of the
   responseValue) is implicitly known and associated with the request by
   the messageID.

   If the extended operation associated with the requestName is not
   supported by the server, the server MUST NOT provide a responseName
   nor a responseValue and MUST return a resultCode of protocolError.

   The requestValue and responseValue fields contain any information
   associated with the operation. The format of these fields is defined
   by the specification of the extended operation. Implementations MUST
   be prepared to handle arbitrary contents of these fields, including
   zero bytes. Values that are defined in terms of ASN.1 and BER encoded
   according to Section 5.2, also follow the extensibility rules in
   Section 4.

   It is RECOMMENDED that servers list the requestName of extended
   operations they support in the 'supportedExtension' attribute of the
   root DSE [Models].

   Extended operations may be specified in other documents. The
   specification of an extended operation consists of:

   - the OBJECT IDENTIFIER assigned to the requestName,

   - the OBJECT IDENTIFIER (if any) assigned to the responseName (note
     that the same OBJECT IDENTIFIER my be used for both the
     requestName and responseName),

   - the format of the contents of the requestValue and responseValue
     (if any), and

   - the semantics of the operation.


4.13. IntermediateResponse Message

   While the Search operation provides a mechanism to return multiple
   response messages for a single search request, other operations, by
   nature, do not provide for multiple response messages.




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   The IntermediateResponse message provides a general mechanism for
   defining single-request/multiple-response operations in LDAP. This
   message is intended to be used in conjunction with the extended
   operation to define new single-request/multiple-response operations
   or in conjunction with a control when extending existing LDAP
   operations in a way that requires them to return intermediate
   response information.

   It is intended that the definitions and descriptions of extended
   operations and controls that make use of the IntermediateResponse
   message will define the circumstances when an IntermediateResponse
   message can be sent by a server and the associated meaning of an
   IntermediateResponse message sent in a particular circumstance.

        IntermediateResponse ::= [APPLICATION 25] SEQUENCE {
                responseName     [0] LDAPOID OPTIONAL,
                responseValue    [1] OCTET STRING OPTIONAL }

   IntermediateResponse messages SHALL NOT be returned to the client
   unless the client issues a request that specifically solicits their
   return. This document defines two forms of solicitation: extended
   operation and request control. IntermediateResponse messages are
   specified in documents describing the manner in which they are
   solicited (i.e. in the extended operation or request control
   specification that uses them). These specifications include:

   - the OBJECT IDENTIFIER (if any) assigned to the responseName,

   - the format of the contents of the responseValue, and

   - the semantics associated with the IntermediateResponse message.

   Extensions that allow the return of multiple types of
   IntermediateResponse messages SHALL identify those types using unique
   responseName values (note that one of these may specify no value).

   Sections 4.13.1 and 4.13.2 describe additional requirements on the
   inclusion of responseName and responseValue in IntermediateResponse
   messages.


4.13.1. Usage with LDAP ExtendedRequest and ExtendedResponse

   A single-request/multiple-response operation may be defined using a
   single ExtendedRequest message to solicit zero or more
   IntermediateResponse messages of one or more kinds followed by an
   ExtendedResponse message.


4.13.2. Usage with LDAP Request Controls

   A control's semantics may include the return of zero or more
   IntermediateResponse messages prior to returning the final result



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   code for the operation.  One or more kinds of IntermediateResponse
   messages may be sent in response to a request control.

   All IntermediateResponse messages associated with request controls
   SHALL include a responseName.  This requirement ensures that the
   client can correctly identify the source of IntermediateResponse
   messages when:

   - two or more controls using IntermediateResponse messages are
     included in a request for any LDAP operation or

   - one or more controls using IntermediateResponse messages are
     included in a request with an LDAP extended operation that uses
     IntermediateResponse messages.


4.14. StartTLS Operation

   The Start Transport Layer Security (StartTLS) operation provides the
   ability to establish a TLS-protected LDAP exchange. The StartTLS
   operation is defined using the extended operation mechanism described
   in Section 4.12.


4.14.1. StartTLS Request

   A client requests TLS establishment by transmitting a StartTLS
   request PDU to the server. The StartTLS request is defined in terms
   of an ExtendedRequest. The requestName is "1.3.6.1.4.1.1466.20037",
   and the requestValue field is always absent.

   The client MUST NOT send any PDUs on this LDAP exchange following
   this request until it receives a StartTLS extended response and, in
   the case of a successful response, completes TLS negotiations.


4.14.2. StartTLS Response

   When a StartTLS request is made, servers supporting the operation
   MUST return a StartTLS response PDU to the requestor. The
   responseName is also "1.3.6.1.4.1.1466.20037", and the responseValue
   field is absent.

   The server provides a resultCode field to either success or one of
   the other values outlined in Section 4.14.2.2.


4.14.2.1. "Success" Response

   If the StartTLS Response contains a resultCode of success, this
   indicates that the server is willing and able to negotiate TLS. Refer
   to Section 4 of [AuthMeth] for details.



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4.14.2.2. Response other than "success"

   If the ExtendedResponse contains a result code other than success,
   this indicates that the server is unwilling or unable to negotiate
   TLS. The following result codes have these meanings for this
   operation:

   - operationsError:  operations sequencing incorrect; e.g. TLS is
                       already established.

   - protocolError:    TLS is not supported or incorrect PDU structure.

   - unavailable:      Some major problem with TLS, or the server is
                       shutting down.

   The server MUST return operationsError if the client violates any of
   the StartTLS extended operation sequencing requirements described in
   Section 4 of [AuthMeth].

   If the server does not support TLS (whether by design or by current
   configuration), it MUST return the protocolError resultCode. In this
   event, the client may proceed with any LDAP operation, or it may
   close the connection.

   The server MUST return unavailable if it supports TLS but cannot
   install the TLS layer for some reason, e.g. the certificate server
   not responding, it cannot contact its TLS implementation, or if the
   server is in process of shutting down. The client may retry the
   StartTLS operation, or it may proceed with any other LDAP operation,
   or it may close the connection.


4.14.3. Removal of the TLS Layer

   Two forms of TLS layer removal -- graceful and abrupt -- are
   supported. These do not involve LDAP PDUs, but are preformed at the
   underlying layers.

   If the connection is closed, uncompleted operations are handled as
   specified in Section 5.1.


4.14.3.1. Graceful Removal

   Either the client or server MAY remove the TLS layer and leave the
   LDAP exchange intact by sending and receiving a TLS closure alert.

   The initiating protocol peer sends the TLS closure alert. If it
   wishes to leave the LDAP exchange intact, it then MUST cease to send




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   further PDUs and MUST ignore any received LDAP PDUs until it receives
   a TLS closure alert from the other peer.

   Once the initiating protocol peer receives a TLS closure alert from
   the other peer it MAY send and receive LDAP PDUs.

   When a protocol peer receives the initial TLS closure alert, it may
   choose to allow the LDAP exchange to remain intact. In this case, it
   MUST immediately transmit a TLS closure alert. Following this, it MAY
   send and receive LDAP PDUs.

   Protocol peers MAY close the connection after sending or receiving a
   TLS closure alert.

   After the TLS layer has been removed, the server MUST NOT send
   responses to any request message received before the TLS closure
   alert. Thus, clients wishing to receive responses to messages sent
   while the TLS layer is intact MUST wait for those message responses
   before sending the TLS closure alert.


4.14.3.2. Abrupt Removal

   Either the client or server MAY abruptly remove the TLS layer by
   closing the connection. In this circumstance, a server MAY send the
   client a Notice of Disconnection before closing the connection.


5. Protocol Encoding, Connection, and Transfer

   This protocol is designed to run over connection-oriented, reliable
   transports, where the data stream is divided into octets (8-bit
   units), with each octet and each bit being significant.

   One underlying service, LDAP over TCP, is defined in Section
   5.3. This service is generally applicable to applications providing
   or consuming X.500-based directory services on the Internet. This
   specification was generally written with the TCP mapping in mind.
   Specifications detailing other mappings may encounter various
   obstacles.

   Implementations of LDAP over TCP MUST implement the mapping as
   described in Section 5.3.

   This table illustrates the relationship between the different layers
   involved in an exchange between two protocol peers:
    +---------------+                       |
    | LDAP exchange |                       |
    +---------------+ > LDAP PDU            |
    +---------------+ < data                |
    |   SASL layer  |                       |
    +---------------+ > SASL-protected data |
    +---------------+ < data                |

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    |   TLS layer   |                       |
    +---------------+ > TLS-protected data  | Application
    +---------------+ < data                +------------
    |   connection  |                       | Transport
    +---------------+


5.2. Protocol Encoding

   The protocol elements of LDAP SHALL be encoded for exchange using the
   Basic Encoding Rules [BER] of [ASN.1] with the following
   restrictions:

   - Only the definite form of length encoding is used.

   - OCTET STRING values are encoded in the primitive form only.

   - If the value of a BOOLEAN type is true, the encoding of the value
     octet is set to hex "FF".

   - If a value of a type is its default value, it is absent. Only some
     BOOLEAN and INTEGER types have default values in this protocol
     definition.

   These restrictions are meant to ease the overhead of encoding and
   decoding certain elements in BER.

   These restrictions do not apply to ASN.1 types encapsulated inside of
   OCTET STRING values, such as attribute values, unless otherwise
   stated.


5.3. Transmission Control Protocol (TCP)

   The encoded LDAPMessage PDUs are mapped directly onto the [TCP]
   bytestream using the BER-based encoding described in Section 5.2. It
   is recommended that server implementations running over the TCP
   provide a protocol listener on the Internet Assigned Numbers
   Authority (IANA)-assigned LDAP port, 389 [PortReg]. Servers may
   instead provide a listener on a different port number. Clients MUST
   support contacting servers on any valid TCP port.


6. Security Considerations

   This version of the protocol provides facilities for simple
   authentication using a cleartext password, as well as any [SASL]
   mechanism. Installing SASL layers can provide integrity and privacy
   services.

   It is also permitted that the server can return its credentials to
   the client, if it chooses to do so.




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   Use of cleartext password is strongly discouraged where the
   underlying transport service cannot guarantee confidentiality and may
   result in disclosure of the password to unauthorized parties.

   Servers are encouraged to prevent directory modifications by clients
   that have authenticated anonymously [AuthMeth].

   Security considerations for authentication methods, SASL mechanisms,
   and TLS are described in [AuthMeth].

   It should be noted that SASL authentication exchanges do not provide
   data confidentiality nor integrity protection for the version or name
   fields of the bind request nor the resultCode, diagnosticMessage, or
   referral fields of the bind response nor of any information contained
   in controls attached to bind request or responses. Thus information
   contained in these fields SHOULD NOT be relied on unless otherwise
   protected (such as by establishing protections at the transport
   layer).

   Server implementors should plan for the possibility of an identity in
   and association being deleted, renamed, or modified, and take
   appropriate actions to prevent insecure side effects. Likewise,
   server implementors should plan for the possibility of an associated
   identity's credentials becoming invalid, or an identity's privileges
   being changed. The ways in which these issues are addressed are
   application and/or implementation specific.

   Implementations which cache attributes and entries obtained via LDAP
   MUST ensure that access controls are maintained if that information
   is to be provided to multiple clients, since servers may have access
   control policies which prevent the return of entries or attributes in
   search results except to particular authenticated clients. For
   example, caches could serve result information only to the client
   whose request caused it to be in the cache.

   Servers may return referrals or search result references which
   redirect clients to peer servers. It is possible for a rogue
   application to inject such referrals into the data stream in an
   attempt to redirect a client to a rogue server. Clients are advised
   to be aware of this, and possibly reject referrals when
   confidentiality measures are not in place. Clients are advised to
   reject referrals from the StartTLS operation.

   The matchedDN and diagnosticMessage fields, as well as some
   resultCode values (e.g., attributeOrValueExists and
   entryAlreadyExists), could disclose the presence the specific data in
   the directory which is subject to access and other administrative
   controls. Server implementations should restrict access to protected
   information equally under both normal and error conditions.

   Protocol peers MUST be prepared to handle invalid and arbitrary
   length protocol encodings. A number of LDAP security advisories are
   available through [CERT].


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7. Acknowledgements

   This document is based on RFC 2251 by Mark Wahl, Tim Howes, and Steve
   Kille. It is also based on RFC 2830 by Jeff Hodges, RL "Bob" Morgan,
   and Mark Wahl. It is also based on RFC 3771 by Roger Harrison, and
   Kurt Zeilenga. Notable amounts of technical reviews and content were
   provided by Kurt Zeilenga, Steven Legg, and Hallvard Furuseth. Their
   work along with the input of individuals of the IETF ASID, LDAPEXT,
   LDUP, LDAPBIS, and other Working Groups is gratefully acknowledged.


8. Normative References

   [ABNF]    Crocker, D. and P. Overell, "Augmented BNF for Syntax
             Specifications: ABNF", RFC 2234, November 1997.

   [ASN.1]   ITU-T Recommendation X.680 (07/2002) | ISO/IEC 8824-1:2002
             "Information Technology - Abstract Syntax Notation One
             (ASN.1): Specification of basic notation"

   [AuthMeth] Harrison, R., "LDAP: Authentication Methods and Connection
             Level Security Mechanisms", draft-ietf-ldapbis-authmeth-
             xx.txt, (a work in progress).

   [BER]     ITU-T Rec. X.690 (07/2002) | ISO/IEC 8825-1:2002,
             "Information technology - ASN.1 encoding rules:
             Specification of Basic Encoding Rules (BER), Canonical
             Encoding Rules (CER) and Distinguished Encoding Rules
             (DER)", 2002.

   [IP]      Postel, J., "Internet Protocol", STD5 and RFC 791,
             September 1981

   [ISO10646] Universal Multiple-Octet Coded Character Set (UCS) -
             Architecture and Basic Multilingual Plane, ISO/IEC 10646-1
             : 1993.

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

   [LDAPDN]  Zeilenga, K., "LDAP: String Representation of
             Distinguished Names", draft-ietf-ldapbis-dn-xx.txt, (a
             work in progress).

   [LDAPIANA] Zeilenga, K., "IANA Considerations for LDAP", draft-ietf-
             ldapbis-bcp64-xx.txt, (a work in progress).

   [LDAPURL] Smith, M., "LDAP: Uniform Resource Locator", draft-ietf-
             ldapbis-url-xx.txt, (a work in progress).

   [Models]  Zeilenga, K., "LDAP: Directory Information Models", draft-
             ietf-ldapbis-models-xx.txt (a work in progress).


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              Lightweight Directory Access Protocol Version 3

   [Roadmap] Zeilenga, K., "LDAP: Technical Specification Road Map",
             draft-ietf-ldapbis-roadmap-xx.txt (a work in progress).

   [SASL]    Melnikov, A., "Simple Authentication and Security Layer",
             draft-ietf-sasl-rfc2222bis-xx.txt (a work in progress).

   [SASLPrep] Zeilenga, K., "Stringprep profile for user names and
             passwords", draft-ietf-sasl-saslprep-xx.txt, (a work in
             progress).

   [StringPrep] Hoffman P. and M. Blanchet, "Preparation of
             Internationalized Strings ('stringprep')", draft-hoffman-
             rfc3454bis-xx.txt, a work in progress.

   [Syntaxes] Legg, S., and K. Dally, "LDAP: Syntaxes and Matching
             Rules", draft-ietf-ldapbis-syntaxes-xx.txt, (a work in
             progress).

   [TCP]     Postel, J., "Transmission Control Protocol", STD7 and RFC
             793, September 1981

   [TLS]     Dierks, T. and C. Allen. "The TLS Protocol Version 1.1",
             draft-ietf-tls-rfc2246-bis-xx.txt, a work in progress.

   [Unicode] The Unicode Consortium, "The Unicode Standard, Version
             3.2.0" is defined by "The Unicode Standard, Version 3.0"
             (Reading, MA, Addison-Wesley, 2000. ISBN 0-201-61633-5),
             as amended by the "Unicode Standard Annex #27: Unicode
             3.1" (http://www.unicode.org/reports/tr27/) and by the
             "Unicode Standard Annex #28: Unicode 3.2"
             (http://www.unicode.org/reports/tr28/).

   [URI]     Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
             Resource Identifiers (URI): Generic Syntax", RFC 2396,
             August 1998.

   [UTF-8]   Yergeau, F., "UTF-8, a transformation format of ISO
             10646", STD63 and RFC3629, November 2003.

   [X.500]   ITU-T Rec. X.500, "The Directory: Overview of Concepts,
             Models and Service", 1993.

   [X.501]   ITU-T Rec. X.501, "The Directory: Models", 1993.

   [X.511]   ITU-T Rec. X.511, "The Directory: Abstract Service
             Definition", 1993.


9. Informative References

   [CERT]    The CERT(R) Center, http://www.cert.org

   [PortReg] IANA, "Port Numbers",
             http://www.iana.org/assignments/port-numbers

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              Lightweight Directory Access Protocol Version 3



10. IANA Considerations

   It is requested that the Internet Assigned Numbers Authority (IANA)
   update the LDAP result code registry to indicate that this document
   provides the definitive technical specification for result codes 0-
   36, 48-54, 64-70, 80-90.

   It is requested that the IANA update the LDAP Protocol Mechanism
   registry to indicate that this document and [AuthMeth] provides the
   definitive technical specification for the Start TLS
   (1.3.6.1.4.1.1466.20037) extended operation.

   It is requested that the IANA update the occurrence of "RFC XXXX" in
   Appendix B with this RFC number at publication.


11. Editor's Address

   Jim Sermersheim
   Novell, Inc.
   1800 South Novell Place
   Provo, Utah 84606, USA
   jimse@novell.com
   +1 801 861-3088






























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Appendix A - LDAP Result Codes

   This normative appendix details additional considerations regarding
   LDAP result codes and provides a brief, general description of each
   LDAP result code enumerated in Section 4.1.9.

   Additional result codes MAY be defined for use with extensions
   [LDAPIANA]. Client implementations SHALL treat any result code which
   they do not recognize as an unknown error condition.


A.1 Non-Error Result Codes

   These result codes (called "non-error" result codes) do not indicate
   an error condition:
        success (0),
        compareFalse (5),
        compareTrue (6),
        referral (10), and
        saslBindInProgress (14).

   The success, compareTrue, and compareFalse result codes indicate
   successful completion (and, hence, are referred to as "successful"
   result codes).

   The referral and saslBindInProgress result codes indicate the client
   is required to take additional action to complete the operation.


A.2 Result Codes

   Existing LDAP result codes are described as follows:

        success (0)
           Indicates the successful completion of an operation. Note:
           this code is not used with the compare operation. See
           compareFalse (5) and compareTrue (6).

        operationsError (1)
           Indicates that the operation is not properly sequenced with
           relation to other operations (of same or different type).

           For example, this code is returned if the client attempts to
           StartTLS [TLS] while there are other uncompleted operations
           or if a TLS layer was already installed.

        protocolError (2)
           Indicates the server received data which is not well-formed.

           For bind operation only, this code is also used to indicate
           that the server does not support the requested protocol
           version.




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           For extended operations only, this code indicates that the
           server does not support (by design or configuration) the
           extended operation associated with the requestName.

           For request operations specifying multiple controls, this may
           be used to indicate that the server cannot ignore the order
           of the controls as specified, or that the combination of the
           specified controls is invalid or unspecified.

        timeLimitExceeded (3)
           Indicates that the time limit specified by the client was
           exceeded before the operation could be completed.

        sizeLimitExceeded (4)
           Indicates that the size limit specified by the client was
           exceeded before the operation could be completed.

        compareFalse (5)
           Indicates that the compare operation has successfully
           completed and the assertion has evaluated to FALSE or
           Undefined.

        compareTrue (6)
           Indicates that the compare operation has successfully
           completed and the assertion has evaluated to TRUE.

        authMethodNotSupported (7)
           Indicates that the authentication method or mechanism is not
           supported.

        strongAuthRequired (8)
           Indicates that the server has detected that an established
           security association between the client and server has
           unexpectedly failed or been compromised, or that the server
           now requires the client to authenticate using a strong(er)
           mechanism.

        referral (10)
           Indicates that a referral needs to be chased to complete the
           operation (see Section 4.1.10).

        adminLimitExceeded (11)
           Indicates that an administrative limit has been exceeded.

        unavailableCriticalExtension (12)
           Indicates that the server is unable or unwilling to perform a
           critical control (see Section 4.1.11).

        confidentialityRequired (13)
           Indicates that data confidentiality protections are required.

        saslBindInProgress (14)




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           Indicates the server requires the client to send a new bind
           request, with the same SASL mechanism, to continue the
           authentication process (see Section 4.2).

        noSuchAttribute (16)
           Indicates that the named entry does not contain the specified
           attribute or attribute value.

        undefinedAttributeType (17)
           Indicates that a request field contains an unrecognized
           attribute description.

        inappropriateMatching (18)
           Indicates that an attempt was made (e.g. in an assertion) to
           use a matching rule not defined for the attribute type
           concerned.

        constraintViolation (19)
           Indicates that the client supplied an attribute value which
           does not conform to the constraints placed upon it by the
           data model.

           For example, this code is returned when multiple values are
           supplied to an attribute which has a SINGLE-VALUE constraint.

        attributeOrValueExists (20)
           Indicates that the client supplied an attribute or value to
           be added to an entry, but the attribute or value already
           exists.

        invalidAttributeSyntax (21)
           Indicates that a purported attribute value does not conform
           to the syntax of the attribute.

        noSuchObject (32)
           Indicates that the object does not exist in the DIT.

        aliasProblem (33)
           Indicates that an alias problem has occurred. For example,
           the code may used to indicate an alias has been dereferenced
           which names no object.

        invalidDNSyntax (34)
           Indicates that an LDAPDN or RelativeLDAPDN field (e.g. search
           base, target entry, ModifyDN newrdn, etc.) of a request does
           not conform to the required syntax or contains attribute
           values which do not conform to the syntax of the attribute's
           type.

        aliasDereferencingProblem (36)
           Indicates that a problem occurred while dereferencing an
           alias. Typically an alias was encountered in a situation
           where it was not allowed or where access was denied.


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        inappropriateAuthentication (48)
           Indicates the server requires the client which had attempted
           to bind anonymously or without supplying credentials to
           provide some form of credentials.

        invalidCredentials (49)
           Indicates that the provided credentials (e.g. the user's name
           and password) are invalid.

        insufficientAccessRights (50)
           Indicates that the client does not have sufficient access
           rights to perform the operation.

        busy (51)
           Indicates that the server is too busy to service the
           operation.

        unavailable (52)
           Indicates that the server is shutting down or a subsystem
           necessary to complete the operation is offline.

        unwillingToPerform (53)
           Indicates that the server is unwilling to perform the
           operation.

        loopDetect (54)
           Indicates that the server has detected an internal loop (e.g.
           while dereferencing aliases or chaining an operation).

        namingViolation (64)
           Indicates that the entry's name violates naming restrictions.

        objectClassViolation (65)
           Indicates that the entry violates object class restrictions.

        notAllowedOnNonLeaf (66)
           Indicates that the operation is inappropriately acting upon a
           non-leaf entry.

        notAllowedOnRDN (67)
           Indicates that the operation is inappropriately attempting to
           remove a value which forms the entry's relative distinguished
           name.

        entryAlreadyExists (68)
           Indicates that the request cannot be fulfilled (added, moved,
           or renamed) as the target entry already exists.

        objectClassModsProhibited (69)
           Indicates that an attempt to modify the object class(es) of
           an entry's 'objectClass' attribute is prohibited.

           For example, this code is returned when a client attempts to
           modify the structural object class of an entry.

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        affectsMultipleDSAs (71)
           Indicates that the operation cannot be performed as it would
           affect multiple servers (DSAs).

        other (80)
           Indicates the server has encountered an internal error.

















































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Appendix B - Complete ASN.1 Definition

        This appendix is normative.

        Lightweight-Directory-Access-Protocol-V3
        -- Copyright (C) The Internet Society (2003). This version of
        -- this ASN.1 module is part of RFC XXXX; see the RFC itself
        -- for full legal notices.
        DEFINITIONS
        IMPLICIT TAGS
        EXTENSIBILITY IMPLIED ::=

        BEGIN

        LDAPMessage ::= SEQUENCE {
             messageID       MessageID,
             protocolOp      CHOICE {
                  bindRequest           BindRequest,
                  bindResponse          BindResponse,
                  unbindRequest         UnbindRequest,
                  searchRequest         SearchRequest,
                  searchResEntry        SearchResultEntry,
                  searchResDone         SearchResultDone,
                  searchResRef          SearchResultReference,
                  modifyRequest         ModifyRequest,
                  modifyResponse        ModifyResponse,
                  addRequest            AddRequest,
                  addResponse           AddResponse,
                  delRequest            DelRequest,
                  delResponse           DelResponse,
                  modDNRequest          ModifyDNRequest,
                  modDNResponse         ModifyDNResponse,
                  compareRequest        CompareRequest,
                  compareResponse       CompareResponse,
                  abandonRequest        AbandonRequest,
                  extendedReq           ExtendedRequest,
                  extendedResp          ExtendedResponse,
                  ...,
                  intermediateResponse  IntermediateResponse },
             controls       [0] Controls OPTIONAL }

        MessageID ::= INTEGER (0 .. maxInt)

        maxInt INTEGER ::= 2147483647 -- (2^^31 - 1) --

        LDAPString ::= OCTET STRING -- UTF-8 encoded,
                                    -- [ISO10646] characters

        LDAPOID ::= OCTET STRING -- Constrained to <numericoid> [Models]

        LDAPDN ::= LDAPString -- Constrained to <distinguishedName>
                              -- [LDAPDN]

        RelativeLDAPDN ::= LDAPString -- Constrained to <name-component>

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                                      -- [LDAPDN]

        AttributeDescription ::= LDAPString
                                -- Constrained to <attributedescription>
                                -- [Models]

        AttributeValue ::= OCTET STRING

        AttributeValueAssertion ::= SEQUENCE {
             attributeDesc   AttributeDescription,
             assertionValue  AssertionValue }

        AssertionValue ::= OCTET STRING

        PartialAttribute ::= SEQUENCE {
             type       AttributeDescription,
             vals       SET OF value AttributeValue }

        Attribute ::= PartialAttribute(WITH COMPONENTS {
             ...,
             vals (SIZE(1..MAX))})

        MatchingRuleId ::= LDAPString

        LDAPResult ::= SEQUENCE {
             resultCode         ENUMERATED {
                  success                      (0),
                  operationsError              (1),
                  protocolError                (2),
                  timeLimitExceeded            (3),
                  sizeLimitExceeded            (4),
                  compareFalse                 (5),
                  compareTrue                  (6),
                  authMethodNotSupported       (7),
                  strongAuthRequired           (8),
                       -- 9 reserved --
                  referral                     (10),
                  adminLimitExceeded           (11),
                  unavailableCriticalExtension (12),
                  confidentialityRequired      (13),
                  saslBindInProgress           (14),
                  noSuchAttribute              (16),
                  undefinedAttributeType       (17),
                  inappropriateMatching        (18),
                  constraintViolation          (19),
                  attributeOrValueExists       (20),
                  invalidAttributeSyntax       (21),
                       -- 22-31 unused --
                  noSuchObject                 (32),
                  aliasProblem                 (33),
                  invalidDNSyntax              (34),
                       -- 35 reserved for undefined isLeaf --
                  aliasDereferencingProblem    (36),
                       -- 37-47 unused --

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                  inappropriateAuthentication  (48),
                  invalidCredentials           (49),
                  insufficientAccessRights     (50),
                  busy                         (51),
                  unavailable                  (52),
                  unwillingToPerform           (53),
                  loopDetect                   (54),
                       -- 55-63 unused --
                  namingViolation              (64),
                  objectClassViolation         (65),
                  notAllowedOnNonLeaf          (66),
                  notAllowedOnRDN              (67),
                  entryAlreadyExists           (68),
                  objectClassModsProhibited    (69),
                       -- 70 reserved for CLDAP --
                  affectsMultipleDSAs          (71),
                       -- 72-79 unused --
                  other                        (80),
                  ... },
             matchedDN          LDAPDN,
             diagnosticMessage  LDAPString,
             referral           [3] Referral OPTIONAL }

        Referral ::= SEQUENCE SIZE (1..MAX) OF uri URI

        URI ::= LDAPString     -- limited to characters permitted in
                               -- URIs

        Controls ::= SEQUENCE OF control Control

        Control ::= SEQUENCE {
             controlType             LDAPOID,
             criticality             BOOLEAN DEFAULT FALSE,
             controlValue            OCTET STRING OPTIONAL }

        BindRequest ::= [APPLICATION 0] SEQUENCE {
             version                 INTEGER (1 .. 127),
             name                    LDAPDN,
             authentication          AuthenticationChoice }

        AuthenticationChoice ::= CHOICE {
             simple                  [0] OCTET STRING,
                                     -- 1 and 2 reserved
             sasl                    [3] SaslCredentials,
             ... }

        SaslCredentials ::= SEQUENCE {
             mechanism               LDAPString,
             credentials             OCTET STRING OPTIONAL }

        BindResponse ::= [APPLICATION 1] SEQUENCE {
             COMPONENTS OF LDAPResult,
             serverSaslCreds    [7] OCTET STRING OPTIONAL }


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        UnbindRequest ::= [APPLICATION 2] NULL

        SearchRequest ::= [APPLICATION 3] SEQUENCE {
             baseObject      LDAPDN,
             scope           ENUMERATED {
                  baseObject              (0),
                  singleLevel             (1),
                  wholeSubtree            (2) },
             derefAliases    ENUMERATED {
                  neverDerefAliases       (0),
                  derefInSearching        (1),
                  derefFindingBaseObj     (2),
                  derefAlways             (3) },
             sizeLimit       INTEGER (0 .. maxInt),
             timeLimit       INTEGER (0 .. maxInt),
             typesOnly       BOOLEAN,
             filter          Filter,
             attributes      AttributeSelection }

        AttributeSelection ::= SEQUENCE OF selector LDAPString
                       -- The LDAPString is constrained to
                       -- <attributeSelection> in Section 4.5.1

        Filter ::= CHOICE {
             and             [0] SET SIZE (1..MAX) OF filter Filter,
             or              [1] SET SIZE (1..MAX) OF filter Filter,
             not             [2] Filter,
             equalityMatch   [3] AttributeValueAssertion,
             substrings      [4] SubstringFilter,
             greaterOrEqual  [5] AttributeValueAssertion,
             lessOrEqual     [6] AttributeValueAssertion,
             present         [7] AttributeDescription,
             approxMatch     [8] AttributeValueAssertion,
             extensibleMatch [9] MatchingRuleAssertion }

        SubstringFilter ::= SEQUENCE {
             type           AttributeDescription,
             -- at least one must be present,
             -- initial and final can occur at most once
             substrings     SEQUENCE SIZE (1..MAX) OF substring CHOICE {
                  initial [0] AssertionValue,
                  any     [1] AssertionValue,
                  final   [2] AssertionValue } }

        MatchingRuleAssertion ::= SEQUENCE {
             matchingRule    [1] MatchingRuleId OPTIONAL,
             type            [2] AttributeDescription OPTIONAL,
             matchValue      [3] AssertionValue,
             dnAttributes    [4] BOOLEAN DEFAULT FALSE }

        SearchResultEntry ::= [APPLICATION 4] SEQUENCE {
             objectName      LDAPDN,
             attributes      PartialAttributeList }


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        PartialAttributeList ::= SEQUENCE OF
                             partialAttribute PartialAttribute

        SearchResultReference ::= [APPLICATION 19] SEQUENCE
                                  SIZE (1..MAX) OF uri URI

        SearchResultDone ::= [APPLICATION 5] LDAPResult

        ModifyRequest ::= [APPLICATION 6] SEQUENCE {
             object          LDAPDN,
             changes         SEQUENCE OF change SEQUENCE {
                  operation       ENUMERATED {
                       add     (0),
                       delete  (1),
                       replace (2) },
                  modification    PartialAttribute } }

        ModifyResponse ::= [APPLICATION 7] LDAPResult

        AddRequest ::= [APPLICATION 8] SEQUENCE {
             entry           LDAPDN,
             attributes      AttributeList }

        AttributeList ::= SEQUENCE OF attribute Attribute

        AddResponse ::= [APPLICATION 9] LDAPResult

        DelRequest ::= [APPLICATION 10] LDAPDN

        DelResponse ::= [APPLICATION 11] LDAPResult

        ModifyDNRequest ::= [APPLICATION 12] SEQUENCE {
             entry           LDAPDN,
             newrdn          RelativeLDAPDN,
             deleteoldrdn    BOOLEAN,
             newSuperior     [0] LDAPDN OPTIONAL }

        ModifyDNResponse ::= [APPLICATION 13] LDAPResult

        CompareRequest ::= [APPLICATION 14] SEQUENCE {
             entry           LDAPDN,
             ava             AttributeValueAssertion }

        CompareResponse ::= [APPLICATION 15] LDAPResult

        AbandonRequest ::= [APPLICATION 16] MessageID

        ExtendedRequest ::= [APPLICATION 23] SEQUENCE {
             requestName      [0] LDAPOID,
             requestValue     [1] OCTET STRING OPTIONAL }

        ExtendedResponse ::= [APPLICATION 24] SEQUENCE {
             COMPONENTS OF LDAPResult,
             responseName     [10] LDAPOID OPTIONAL,

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             responseValue    [11] OCTET STRING OPTIONAL }

        IntermediateResponse ::= [APPLICATION 25] SEQUENCE {
             responseName     [0] LDAPOID OPTIONAL,
             responseValue    [1] OCTET STRING OPTIONAL }

        END

















































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Appendix C - Changes

   This appendix is non-normative.

   This appendix summarizes substantive changes made to RFC 2251 and RFC
   2830.


C.1 Changes made to RFC 2251:

   This section summarizes the substantive changes made to Sections 1,
   2, 3.1, and 4 through the remainder of RFC 2251. Readers should
   consult [Models] and [AuthMeth] for summaries of changes to other
   sections.


C.1.1 Section 1

   - Removed IESG note. Post publication of RFC 2251, mandatory LDAP
     authentication mechanisms have been standardized which are
     sufficient to remove this note. See [AuthMeth] for authentication
     mechanisms.


C.1.2 Section 3.1 and others

   - Removed notes giving history between LDAP v1, v2 and v3. Instead,
     added sufficient language so that this document can stand on its
     own.


C.1.3 Section 4

   - Clarified where the extensibility features of ASN.1 apply to the
     protocol. This change also affected various ASN.1 types.
   - Removed the requirement that servers which implement version 3 or
     later MUST provide the 'supportedLDAPVersion' attribute. This
     statement provided no interoperability advantages.


C.1.4 Section 4.1.1

   - There was a mandatory requirement for the server to return a
     Notice of Disconnection and drop the connection when a PDU is
     malformed in a certain way. This has been clarified such that the
     server SHOULD return the Notice of Disconnection, and MUST drop
     the connection.


C.1.5 Section 4.1.1.1

   - Clarified that the messageID of requests MUST be non-zero.




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   - Clarified when it is and isn't appropriate to return an already
     used message id. RFC 2251 accidentally imposed synchronous server
     behavior in its wording of this.


C.1.6 Section 4.1.2

   - Stated that LDAPOID is constrained to <numericoid> from [Models].


C.1.7 Section 4.1.5.1

   - Removed the Binary Option from the specification. There are
     numerous interoperability problems associated with this method of
     alternate attribute type encoding. Work to specify a suitable
     replacement is ongoing.


C.1.8 Section 4.1.6

   - Removed references to the "binary" encoding as it has been removed
     from the specification.


C.1.9 Section 4.1.7

   - Removed references to the "binary" encoding as it has been removed
     from the specification.


C.1.10 Section 4.1.8

   - Combined the definitions of PartialAttribute and Attribute here,
     and defined Attribute in terms of PartialAttribute.


C.1.11 Section 4.1.10

   - Renamed "errorMessage" to "diagnosticMessage" as it is allowed to
     be sent for non-error results.
   - Moved some language into Appendix A, and refer the reader there.
   - Allowed matchedDN to be present for other result codes than those
     listed in RFC 2251.


C.1.12 Section 4.1.11

   - Defined referrals in terms of URIs rather than URLs.
   - Removed the requirement that all referral URIs MUST be equally
     capable of progressing the operation. The statement was ambiguous
     and provided no instructions on how to carry it out.
   - Added the requirement that clients MUST NOT loop between servers.
   - Clarified the instructions for using LDAPURLs in referrals, and in
     doing so added a recommendation that the scope part be present.

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C.1.13 Section 4.1.12

   - Specified how control values defined in terms of ASN.1 are to be
     encoded.
   - Noted that the criticality field is only applied to request
     messages (except unbindRequest), and must be ignored when present
     on response messages and unbindRequest.
   - Added language regarding combinations of controls and the ordering
     of controls on a message.
   - Specified that when the semantics of the combination of controls
     is undefined or unknown, it results in a protocolError.
   - Changed "The server MUST be prepared" to "Implementations MUST be
     prepared" in the eighth paragraph to reflect that both client and
     server implementations must be able to handle this (as both parse
     controls).


C.1.14 Section 4.2

   - Mandated that servers return protocolError when the version is not
     supported.
   - Clarified behavior when the simple authentication is used, the
     name is empty and the password is non-empty.
   - Required servers to not dereference aliases for bind. This was
     added for consistency with other operations and to help ensure
     data consistency.
   - Required that textual passwords be transferred as UTF-8 encoded
     Unicode, and added recommendations on string preparation. This was
     to help ensure interoperability of passwords being sent from
     different clients.


C.1.15 Section 4.2.1

   - This section was largely reorganized for readability and language
     was added to clarify the authentication state of failed and
     abandoned bind operations.
   - Removed: "If a SASL transfer encryption or integrity mechanism has
     been negotiated, that mechanism does not support the changing of
     credentials from one identity to another, then the client MUST
     instead establish a new connection."
     Each SASL negotiation is, generally, independent of other SASL
     negotiations. If there were dependencies between multiple
     negotiations of a particular mechanism, the mechanism technical
     specification should detail how applications are to deal with
     them. LDAP should not require any special handling. And if an LDAP
     client had used such a mechanism, it would have the option of
     using another mechanism.
   - Dropped MUST imperative in paragraph 3 to align with [Keywords].
   - Mandated that clients not send non-bind operations while a bind is
     in progress, and suggested that servers not process them if they



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     are received. This is needed to ensure proper sequencing of the
     bind in relationship to other operations.


C.1.16 Section 4.2.3

   - Moved most error-related text to Appendix A, and added text
     regarding certain errors used in conjunction with the bind
     operation.
   - Prohibited the server from specifying serverSaslCreds when not
     appropriate.


C.1.17 Section 4.3

   - Required both peers to cease transmission and close the LDAP
     exchange for the unbind operation.


C.1.18 Section 4.4

   - Added instructions for future specifications of Unsolicited
     Notifications.


C.1.19 Section 4.5.1

   - SearchRequest attributes is now defined as an AttributeSelection
     type rather than AttributeDescriptionList, and an ABNF is
     provided.
   - SearchRequest attributes may contain duplicate attribute
     descriptions. This was previously prohibited. Now servers are
     instructed to ignore subsequent names when they are duplicated.
     This was relaxed in order to allow different short names and also
     OIDs to be requested for an attribute.
   - The Filter choices 'and' and 'or', and the SubstringFilter
     substrings types are now defined with a lower bound of 1.
   - The SubstringFilter substrings 'initial, 'any', and 'final' types
     are now AssertionValue rather than LDAPString. Also, added
     imperatives stating that 'initial' (if present) must be listed
     first, and 'final' (if present) must be listed last.
   - Clarified the semantics of the derefAliases choices.
   - Added instructions for equalityMatch, substrings, greaterOrEqual,
     lessOrEqual, and approxMatch.


C.1.20 Section 4.5.2

   - Recommended that servers not use attribute short names when it
     knows they are ambiguous or may cause interoperability problems.
   - Removed all mention of ExtendedResponse due to lack of
     implementation.



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C.1.21 Section 4.5.3

   - Made changes similar to those made to Section 4.1.11.


C.1.22 Section 4.5.3.1

   - Fixed examples to adhere to changes made to Section 4.5.3.


C.1.23 Section 4.6

   - Removed restriction that required an EQUALITY matching rule in
     order to perform value delete modifications. It is sufficiently
     documented that in absence of an equality matching rule, octet
     equality is used.
   - Replaced AttributeTypeAndValues with Attribute as they are
     equivalent.
   - Clarified what type of modification changes might temporarily
     violate schema.


C.1.24 Section 4.7

   - Aligned Add operation with X.511 in that the attributes of the RDN
     are used in conjunction with the listed attributes to create the
     entry. Previously, Add required that the distinguished values be
     present in the listed attributes.


C.1.25 Section 4.9

   - Required servers to not dereference aliases for modify DN. This
     was added for consistency with other operations and to help ensure
     data consistency.
   - Allow modify DN to fail when moving between naming contexts.
   - Specified what happens when the attributes of the newrdn are no
     present on the entry.


C.1.26 Section 4.10

   - Clarified that compareFalse means that the compare took place and
     the result is false. There was confusion which lead people to
     believe that an Undefined match resulted in compareFalse.
   - Required servers to not dereference aliases for compare. This was
     added for consistency with other operations and to help ensure
     data consistency.


C.1.27 Section 4.11

   - Explained that since abandon returns no response, clients should
     not use it if they need to know the outcome.

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   - Specified that Abandon and Unbind cannot be abandoned.


C.1.28 Section 4.12

   - Specified how values of extended operations defined in terms of
     ASN.1 are to be encoded.
   - Added instructions on what extended operation specifications
     consist of.
   - Added a recommendation that servers advertise supported extended
     operations.


C.1.29 Section 5.2

   - Moved referral-specific instructions into referral-related
     sections.


C.1.30 Section 7

   - Reworded notes regarding SASL not protecting certain aspects of
     the LDAP bind PDU.
   - Noted that Servers are encouraged to prevent directory
     modifications by clients that have authenticated anonymously
     [AuthMeth].
   - Added a note regarding the scenario where an identity is changed
     (deleted, privileges or credentials modified, etc.).
   - Warned against following referrals that may have been injected in
     the data stream.
   - Noted that servers should protect information equally, whether in
     an error condition or not, and mentioned specifically; matchedDN,
     diagnosticMessage, and resultCodes.
   - Added a note regarding malformed and long encodings.


C.1.31 Appendix A

   - Added "EXTESIBILITY IMPLIED" to ASN.1 definition.
   - Removed AttributeType. It is not used.


C.2 Changes made to RFC 2830:

   This section summarizes the substantive changes made to Sections of
   RFC 2830. Readers should consult [AuthMeth] for summaries of changes
   to other sections.


C.2.1 Section 2.3

   - Removed wording indicating that referrals can be returned from
     StartTLS



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   - Removed requirement that only a narrow set of result codes can be
     returned. Some result codes are required in certain scenarios, but
     any other may be returned if appropriate.


C.2.1 Section 4.13.3.1

   - Reworded most of this section and added the requirement that after
     the TLS connection has been closed, the server MUST NOT send
     responses to any request message received before the TLS closure.


C.3 Changes made to RFC 3771:

   - In general, all technical language was transferred in whole.
     Supporting and background language seen as redundant due to its
     presence in this document was omitted.







































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