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Internet-Draft                                  Editor:  J. Sermersheim
Intended Category: Standard Track                           Novell, Inc
Document: draft-ietf-ldapbis-protocol-09.txt                   Oct 2002
Obsoletes: RFC 2251


                            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, for 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
   2. Conventions......................................................3
   3. Protocol Model...................................................3
   4. Elements of Protocol.............................................3
   4.1. Common Elements................................................4
   4.1.1. Message Envelope.............................................4
   4.1.2. String Types.................................................5
   4.1.3. Distinguished Name and Relative Distinguished Name...........6

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  4.1.4. Attribute Descriptions.......................................6
  4.1.5. Attribute Value..............................................7
  4.1.6. Attribute Value Assertion....................................7
  4.1.7. Attribute....................................................7
  4.1.8. Matching Rule Identifier.....................................8
  4.1.9. Result Message...............................................8
  4.1.10. Referral...................................................10
  4.1.11. Controls...................................................11
  4.2. Bind Operation................................................12
  4.3. Unbind Operation..............................................15
  4.4. Unsolicited Notification......................................15
  4.5. Search Operation..............................................16
  4.6. Modify Operation..............................................23
  4.7. Add Operation.................................................25
  4.8. Delete Operation..............................................26
  4.9. Modify DN Operation...........................................26
  4.10. Compare Operation............................................27
  4.11. Abandon Operation............................................28
  4.12. Extended Operation...........................................29
  5. Protocol Element Encodings and Transfer.........................29
  5.1. Protocol Encoding.............................................29
  5.2. Transfer Protocols............................................30
  6. Implementation Guidelines.......................................30
  6.1. Server Implementations........................................30
  6.2. Client Implementations........................................30
  7. Security Considerations.........................................31
  8. Acknowledgements................................................31
  9. Normative References............................................31
  10. Editor's Address...............................................32
  Appendix A - LDAP Result Codes.....................................33
  A.1 Non-Error Result Codes.........................................33
  A.2 Error Result Codes.............................................33
  A.3 Classes and Precedence of Error Result Codes...................33
  Appendix C - Change History........................................44
  C.1 Changes made to RFC 2251:......................................44
  C.2 Changes made to draft-ietf-ldapbis-protocol-00.txt:............44
  C.3 Changes made to draft-ietf-ldapbis-protocol-01.txt:............45
  C.4 Changes made to draft-ietf-ldapbis-protocol-02.txt:............45
  C.5 Changes made to draft-ietf-ldapbis-protocol-03.txt:............47
  C.6 Changes made to draft-ietf-ldapbis-protocol-04.txt:............49
  C.7 Changes made to draft-ietf-ldapbis-protocol-05.txt:............49
  C.8 Changes made to draft-ietf-ldapbis-protocol-06.txt:............50
  C.9 Changes made to draft-ietf-ldapbis-protocol-07.txt:............53
  C.10 Changes made to draft-ietf-ldapbis-protocol-07.txt:...........53
  Appendix D - Outstanding Work Items................................53


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

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  (DSA)). Clients interact with servers using a directory access
  protocol.

  This document details the protocol elements of Lightweight Directory
  Access Protocol, along with their semantic meanings. Following the
  description of protocol elements, it describes the way in which the
  protocol is encoded and transferred.

  This document is an integral part of the LDAP Technical Specification
  [Roadmap].

  This document replaces RFC 2251. Appendix C holds a detailed log of
  changes to RFC 2251. At publication time, this appendix will be
  distilled to a summary of changes to RFC 2251.


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 [RFC2119].


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 the
  operation(s), the server returns a response containing any results or
  errors to the requesting client.

  Note that 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 may be exchanged
  between a client and server in any order, provided the client
  eventually receives a response for every request that requires one.

  Note that the core protocol operations defined in this document can
  be mapped to a subset of the X.500(1997) directory abstract service.
  However there is not a one-to-one mapping between LDAP protocol
  operations and DAP operations. Server implementations acting as a
  gateway to X.500 directories may need to make multiple DAP requests.


4. Elements of Protocol

  The LDAP protocol is described using Abstract Syntax Notation 1
  (ASN.1) [X.680], and is transferred using a subset of ASN.1 Basic
  Encoding Rules [X.690]. Section 5.1 specifies how the protocol is
  encoded and transferred.


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  In order to support future Standards Track extensions to this
  protocol, extensibility is implied where it is allowed (per ASN.1).
  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 ignore trailing
  SEQUENCE elements whose tags they do not recognize.

  Changes to the LDAP protocol other than those described in [LDAPIANA]
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  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
  [Models]. Servers which implement version 3 or later MUST provide
  this attribute.


4.1. Common Elements

  This section describes the LDAPMessage envelope PDU (Protocol Data
  Unit) 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,

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                    extendedResp    ExtendedResponse,
                    ... },
             controls      [0] Controls OPTIONAL }

      MessageID ::= INTEGER (0 .. maxInt)

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

  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 MAY return the Notice of Disconnection
  described in section 4.4.1, with resultCode 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.

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


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 requests outstanding in the LDAP session 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 connection unless it can be determined
  that the server is no longer servicing the earlier request. Otherwise
  the behavior is undefined. For operations that do not return
  responses (unbind, abandon, and abandoned operations), the client
  SHOULD assumes the operation is in progress until a subsequent bind
  request completes.


4.1.2. String Types

  The LDAPString is a notational convenience to indicate that, although
  strings of LDAPString type encode as OCTET STRING types, the

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  [ISO10646] character set (a superset of Unicode) is used, encoded
  following the UTF-8 algorithm [RFC2044]. Note that in the UTF-8
  algorithm characters which are the same as ASCII (0x0000 through
  0x007F) are represented as that same ASCII character in a single
  byte. The other byte values are used to form a variable-length
  encoding of an arbitrary character.

      LDAPString ::= OCTET STRING -- UTF-8 encoded,
                                  -- ISO 10646 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 1.3 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 and a RelativeLDAPDN are respectively defined to be the
  representation of a distinguished-name and a relative-distinguished-
  name after encoding according to the specification in [LDAPDN].

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


  Not all options can be associated with attributes held in the
  directory. A server will treat an AttributeDescription with any
  options it does not implement or support as unrecognized. The order
  in which options appear in the list MUST NOT be used to impart any
  semantic meaning. Servers MUST treat any two AttributeDescription
  with the same attribute type and options as equivalent.


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  AttributeDescriptionList describes a list of 0 or more attribute
  descriptions. (A list of zero elements has special significance in
  the Search request.)

      AttributeDescriptionList ::= SEQUENCE OF
             AttributeDescription


4.1.5. Attribute Value

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

      AttributeValue ::= OCTET STRING

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

  Attributes may be defined which have arbitrary and non-printable
  syntax. Implementations MUST NOT display nor attempt to decode as
  ASN.1, a value if its syntax is not known. The implementation may
  attempt to discover the subschema of the source entry, and retrieve
  the values of attributeTypes from it.

  Clients MUST NOT send attribute values in a request that are not
  valid according to the syntax defined for the attributes.


4.1.6. Attribute Value Assertion

  The AttributeValueAssertion type definition is similar to the one in
  the X.500 directory standards. It contains an attribute description
  and a matching rule assertion value suitable for that type.

      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

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  An attribute consists of an attribute description and one or more
  values of that attribute description. (Though attributes MUST have at
  least one value when stored, due to access control restrictions the
  set may be empty when transferred from the server to the client. This
  is described in section 4.5.2, concerning the PartialAttributeList
  type.)

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

  Each attribute value is distinct in the set (no duplicates). The set
  of attribute values is unordered. Implementations MUST NOT reply upon
  any apparent ordering being repeatable.


4.1.8. Matching Rule Identifier

  Matching rules are defined in 4.1.3 of [Models]. A matching rule is
  identified in the LDAP protocol by the printable representation of
  either its numericoid, or one of its short name descriptors, e.g.
  "caseIgnoreIA5Match" or "1.3.6.1.4.1.453.33.33".

      MatchingRuleId ::= LDAPString

  Servers which support matching rules for use in the extensibleMatch
  search filter MUST list the matching rules they implement in
  subschema entries, using the matchingRules attributes. The server
  SHOULD also list there, using the matchingRuleUse attribute, the
  attribute types with which each matching rule can be used. More
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  information is given in section 4.5 of [Syntaxes].


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 LDAPResponse 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 --

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                    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),
                    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),
                    ... },
                    -- 81-90 reserved for APIs --
             matchedDN       LDAPDN,
             errorMessage    LDAPString,
             referral        [3] Referral OPTIONAL }

  The result codes enumeration is extensible as defined in Section 3.5
  of [LDAPIANA]. The meanings of the result codes are given in Appendix
  A.

  The errorMessage 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)
  error diagnostic. As this error diagnostic is not standardized,
  implementations MUST NOT rely on the values returned. If the server
  chooses not to return a textual diagnostic, the errorMessage field of
  the LDAPResult type MUST contain a zero length string.


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  For result codes of 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]. The matchedDN field contains a zero length string with
  all other result codes.


4.1.10. Referral

  The referral result code indicates that the contacted server does not
  hold the target entry of the request. The referral field is present
  in an LDAPResult if the LDAPResult.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 URL 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 the search scope spans multiple naming contexts, and several
  different servers would need to be contacted to complete the
  operation.

      Referral ::= SEQUENCE OF LDAPURL  -- one or more

       LDAPURL ::= LDAPString -- limited to characters permitted in
                          -- URLs

  If the client wishes to progress the operation, it MUST follow the
  referral by contacting one of the servers. If multiple URLs are
  present, the client assumes that any URL may be used to progress the
  operation.

  URLs for servers implementing the LDAP protocol are written according
  to [LDAPDN]. If an alias was dereferenced, the <dn> part of the URL
  MUST be present, with the new target object name. 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. Some servers (e.g.
  participating in distributed indexing) may provide a different filter
  in a referral for a search operation. If the filter part of the URL
  is present in an LDAPURL, 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. Other aspects of
  the new request may be the same or different as the request which
  generated the referral.


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  Note that UTF-8 characters appearing in a DN or search filter may not
  be legal for URLs (e.g. spaces) and MUST be escaped using the %
  method in [RFC2396].

  Other kinds of URLs may be returned, so long as the operation could
  be performed using that protocol.


4.1.11. Controls

  A control is a way to specify extension information for an LDAP
  message. A control only alters the semantics of the message it is
  attached to.

      Controls ::= SEQUENCE OF Control

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

  The controlType field MUST be a UTF-8 encoded dotted-decimal
  representation of an OBJECT IDENTIFIER which uniquely identifies the
  control. This prevents conflicts between control names.

  The criticality field is either TRUE or FALSE and only applies to
  request messages that have a corresponding response message. For all
  other messages (such as abandonRequest, unbindRequest and all
  response messages), the criticality field is treated as FALSE.

  If the server recognizes the control type and it is appropriate for
  the operation, the server will 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 MUST instead return the
  resultCode unavailableCriticalExtension.

  If the control is unrecognized or inappropriate but the criticality
  field is FALSE, the server MUST ignore the control.

  The controlValue contains any information associated with the
  control, and its format is defined for 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.

  This document does not specify any controls. Controls may be
  specified in other documents. The specification of a control consists
  of:

  - the OBJECT IDENTIFIER assigned to the control,


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  - whether the control is always noncritical, always critical, or
    critical at the client's option,

  - the format of the controlValue contents of the control,

  - the semantics of the control,

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

  Servers list the controlType of all controls they recognize in the
  supportedControl attribute [Models] in the root DSE.

  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. In the absence of combination
  semantics, the behavior of the operation is undefined.
  Additionally, the order of a combination of controls in the SEQUENCE
  is ignored unless the control specification(s) describe(s)
  combination semantics.


4.2. Bind Operation

  The function of the Bind Operation is to allow authentication
  information to be exchanged between the client and server. Prior to
  the BindRequest, the implied identity is anonymous. Refer to
  [AuthMeth] for the authentication-related semantics of this
  operation.

  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 }

  Parameters of the Bind Request are:

  - version: A version number indicating the version of the protocol
    to be used in this protocol session. This document describes
    version 3 of the LDAP protocol. Note that there is no version
    negotiation, and the client just sets this parameter to the

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    version it desires. If the server does not support the specified
    version, it responds 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, when authentication
    has been performed at a lower layer, or when using SASL
    credentials with a mechanism that includes the name in the
    credentials. Server behavior is undefined when the name is a null
    value, simple authentication is used, and a password is specified.
    The server SHOULD NOT perform any alias dereferencing in
    determining the object to bind as.

  - authentication: information used to authenticate the name, if any,
    provided in the Bind Request. This type is extensible as defined
    in Section 3.6 of [LDAPIANA]. Servers that do not support a choice
    supplied by a client will return authMethodNotSupported in the
    result code of the BindResponse.

  Upon receipt of a Bind Request, a protocol server will authenticate
  the requesting client, if necessary. The server will then return a
  Bind Response to the client indicating the status of the
  authentication.

  Authorization is the use of this authentication information when
  performing operations. Authorization MAY be affected by factors
  outside of the LDAP Bind request, such as lower layer security
  services.


4.2.1. Sequencing of the Bind Request

  For some SASL authentication mechanisms, it may be necessary for the
  client to invoke the BindRequest multiple times. If at any stage the
  client wishes to abort the bind process it MAY unbind and then drop
  the underlying connection. 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
  authMethodNotSupported as the resultCode. This will allow clients to
  abort a negotiation if it wishes to try again with the same SASL
  mechanism.

  If the client did not bind before sending a request and receives an
  operationsError, it may then send a Bind Request. If this also fails
  or the client chooses not to bind on the existing connection, it will
  close the connection, reopen it and begin again by first sending a

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            Lightweight Directory Access Protocol Version 3

  PDU with a Bind Request. This will aid in interoperating with servers
  implementing other versions of LDAP.


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.

  If the bind was successful, the resultCode will be success, otherwise
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  it MAY be one of:
                                                                  d
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                                                                   f
                                                                    t
                                                                    .

  - operationsError: server encountered an internal error.

  - protocolError: unrecognized version number or incorrect PDU
    structure.

  - authMethodNotSupported: unrecognized SASL mechanism name.

  - strongAuthRequired: the server requires authentication be
    performed with a SASL mechanism.

  - referral: this server cannot accept this bind and the client
    should try another.

  - saslBindInProgress: the server requires the client to send a new
    bind request, with the same sasl mechanism, to continue the
    authentication process.

  - inappropriateAuthentication: the server requires the client which
    had attempted to bind anonymously or without supplying credentials
    to provide some form of credentials.

  - invalidCredentials: the wrong password was supplied or the SASL
    credentials could not be processed.

  - unavailable: the server is shutting down.

  If the server does not support the client's requested protocol
  version, it MUST set the resultCode to protocolError.

  If the client receives a BindResponse response where the resultCode
  was protocolError, it MUST close the connection as the server will be
  unwilling to accept further operations. (This is for compatibility
  with earlier versions of LDAP, in which the bind was always the first
  operation, and there was no negotiation.)


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            Lightweight Directory Access Protocol Version 3

  The serverSaslCreds are 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 is not to be included in the result.


4.3. Unbind Operation

  The function of the Unbind Operation is to terminate a protocol
  session. The Unbind Operation is defined as follows:

       UnbindRequest ::= [APPLICATION 2] NULL

  The Unbind Operation has no response defined. Upon transmission of an
  UnbindRequest, a protocol client MUST assume that the protocol
  session is terminated. Upon receipt of an UnbindRequest, a protocol
  server MUST assume that the requesting client has terminated the
  session and that all outstanding requests may be discarded, and MUST
  close the connection.


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 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 0 and protocolOp is of the extendedResp form. The
  responseName field of the ExtendedResponse is present. The LDAPOID
  value MUST be unique for this notification, and not be used in any
  other situation.

  One unsolicited notification (Notice of Disconnection) is defined in
  this document.


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. Note that this notification is NOT a response to an unbind
  requested by the client: the server MUST follow the procedures of
  section 4.3. This notification is intended to assist clients in
  distinguishing between an error condition and a transient network
  failure. As with a connection close due to network failure, the
  client MUST NOT assume that any outstanding requests which modified
  the directory have succeeded or failed.


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  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.

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  The following resultCode values are to be used in this notification:
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  - protocolError: The server has received data from the client in
    which the LDAPMessage structure could not be parsed.

  - strongAuthRequired: The server has detected that an established
    underlying security association protecting communication between
    the client and server has unexpectedly failed or been compromised.

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

  After sending this notice, the server MUST close the connection.
  After receiving this notice, the client MUST NOT transmit any further
  on the connection, and may abruptly close the connection.


4.5. Search Operation

  The Search Operation allows a client to request that a search be
  performed on its behalf by a server. This can be used to read
  attributes from a single entry, from entries immediately below 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      AttributeDescriptionList }

       Filter ::= CHOICE {
               and             [0] SET SIZE (1..MAX) OF Filter,

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            Lightweight Directory Access Protocol Version 3

               or              [1] SET SIZE (1..MAX) OF 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 OF 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 }

  Parameters of the Search Request are:

  - baseObject: An LDAPDN that is the base object entry relative to
    which the search is to be performed.

  - scope: An indicator of the scope of the search to be performed.
    The semantics of the possible values of this field are identical
    to the semantics of the scope field in the X.511 Search Operation.

  - derefAliases: An indicator as to how alias objects (as defined in
    X.501) 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: dereference aliases in subordinates of
           the base object in searching, but not in locating the base
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           object of the search;
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           derefFindingBaseObj: dereference aliases in locating the
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           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.

  - sizeLimit: A size limit that restricts the maximum number of
    entries to be returned as a result of the search. A value of 0 in

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            Lightweight Directory Access Protocol Version 3

    this field indicates that no client-requested size limit
    restrictions are in effect for the search. Servers may 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 0 in this field
    indicates that no client-requested time limit restrictions are in
    effect for the search.

  - typesOnly: An indicator as to whether search results will contain
    both attribute types and values, or just attribute types. Setting
    this field to TRUE causes only attribute types (no values) to be
    returned. Setting this field to FALSE causes both attribute types
    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
    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 and assertion syntax for equalityMatch filter
    items is defined by the EQUALITY matching rule for the attribute
    type.

    The matching rule and assertion syntax for AssertionValues in a
    substrings filter item is defined by the SUBSTR matching rule for
    the attribute type.

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    The matching rule and assertion syntax for greaterOrEqual and
    lessOrEqual filter items is defined by the ORDERING matching rule
    for the attribute type.

    The matching rule and assertion syntax for approxMatch filter
    items is implementation-defined. If approximate matching is not
    supported by the server, the filter item should be treated as an
    equalityMatch.

    The extensibleMatch is new in this version of LDAP. If the
    matchingRule field is absent, the type field MUST be present, and
    the equality match is performed for that type. If the type field
    is absent and matchingRule is present, the matchValue is compared
    against all attributes in an entry which support that
    matchingRule, and 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 cannot be
    parsed.) If the type field is present and matchingRule is present,
    the matchingRule MUST be one permitted for use with that type,
    otherwise the filter item is undefined. If the dnAttributes field
    is set to TRUE, the match is applied against all the attributes in
    an entry's distinguished name as well, and also evaluates to TRUE
    if there is at least one attribute in the distinguished name for
    which the filter item evaluates to TRUE. (Editors note: The
    dnAttributes field is present so that there does not need to be
    multiple versions of generic matching rules such as for word
    matching, one to apply to entries and another to apply 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 cannot be parsed, 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, or assertion values cannot
    be parsed. More details of filter processing are given in section
    7.8 of [X.511].

  - attributes: A list of the attributes to be returned from each
    entry which matches the search filter. There are two special
    values which may be used: an empty list with no attributes, and
    the attribute description string "*". Both of these signify that

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    all user attributes are to be returned. (The "*" allows the client
    to request all user attributes in addition to any specified
    operational attributes).

    Attributes MUST be named at most once in the list, and are
    returned at most once in an entry. If there are attribute
    descriptions in the list which are not recognized, they are
    ignored by the server.

    If the client does not want any attributes returned, it can
    specify a list containing only the attribute with OID "1.1". This
    OID was chosen arbitrarily and does not correspond to any
    attribute in use.

    Client implementors should note that even if all user attributes
    are requested, some attributes 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, since there may be extremely large number of values for
    certain operational attributes. (A list of operational attributes
    for use in LDAP is given in [Syntaxes].)

  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 attempted by the server upon receipt of a
  Search Request are returned in Search Responses, which are LDAP
  messages containing either SearchResultEntry, SearchResultReference,
  or SearchResultDone data types.

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

       PartialAttributeList ::= SEQUENCE OF SEQUENCE {
               type    AttributeDescription,
               vals    SET OF AttributeValue }
       -- implementors should note that the PartialAttributeList may
       -- have zero elements (if none of the attributes of that entry
       -- were requested, or could be returned), and that the vals set
       -- may also have zero elements (if types only was requested, or
       -- all values were excluded from the result.)

       SearchResultReference ::= [APPLICATION 19] SEQUENCE OF LDAPURL

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            Lightweight Directory Access Protocol Version 3

       -- at least one LDAPURL element must be present

       SearchResultDone ::= [APPLICATION 5] LDAPResult

  Upon receipt of a Search Request, a server will perform the necessary
  search of the DIT.

  If the LDAP session is operating over a connection-oriented transport
  such as TCP, the server will return to the client a sequence of
  responses in separate LDAP messages. There may be zero or more
  responses containing SearchResultEntry, one for each entry found
  during the search. There may also be zero or more responses
  containing SearchResultReference, one for each area not explored by
  this server during the search. The SearchResultEntry and
  SearchResultReference PDUs may come in any order. Following all the
  SearchResultReference responses and all SearchResultEntry responses
  to be returned by the server, the server will return a response
  containing the SearchResultDone, which contains an indication of
  success, or detailing any errors that have occurred.

  Each entry returned in a SearchResultEntry will contain all
  attributes, complete with associated values if necessary, 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 serverÆs schema defines a textual name for an attribute type,
  it MUST use a textual name for attributes of that attribute type by
  specifying one of the textual names as the value of the attribute
  type. Otherwise, the server uses the object identifier for the
  attribute type by specifying the object identifier, in ldapOID form,
  as the value of attribute type.


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 all the entries in the scope at
  and under the baseObject, 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 a referral resultCode.

  In the absence of indexing information provided to a server from
  servers holding subordinate naming contexts, SearchResultReference
  responses are not affected by search filters and are always returned
  when in scope.

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            Lightweight Directory Access Protocol Version 3


  The SearchResultReference is of the same data type as the Referral.
  URLs for servers implementing the LDAP protocol are written according
  to [LDAPDN]. The <dn> part MUST be present in the URL, with the new
  target object name. The client MUST use this name in its next
  request. Some servers (e.g. part of a distributed index exchange
  system) may provide a different filter in the URLs of the
  SearchResultReference. If the filter part of the URL is present in an
  LDAP URL, the client MUST use the new filter in its next request to
  progress the search, and if the filter part is absent the client will
  use again the same filter. If the originating search scope was
  singleLevel, the scope part of the URL will be baseObject. Other
  aspects of the new search request may be the same or different as the
  search which generated the continuation references.
  Other kinds of URLs may be returned so long as the operation could be
  performed using that protocol.

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

  In order to complete the search, the client MUST issue 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 a connection between a client and
  server, and if the client has multiple outstanding search operations,
  it MUST abandon each operation individually.


4.5.3.1. Example

  For example, suppose the contacted server (hosta) holds the entry
  "DC=Example,DC=NET" and the entry "CN=Manager,DC=Example,DC=NET". It
  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 subtree 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
      ldap://hostc/OU=People,DC=Example,DC=NET
    }
    SearchResultReference {
      ldap://hostd/OU=Roles,DC=Example,DC=NET
    }
    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

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            Lightweight Directory Access Protocol Version 3

  (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
    }
    SearchResultReference {
      ldap://hostf/OU=Consultants,OU=People,DC=Example,DC=NET
    }
    SearchResultDone (success)

  If the contacted server does not hold the base object for the search,
  then it will return a referral to the client. For example, if the
  client requests a subtree search of "DC=Example,DC=ORG" to hosta, the
  server may return only a SearchResultDone containing a referral.

    SearchResultDone (referral) {
      ldap://hostg/
    }


4.6. Modify Operation

  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,
               modification    SEQUENCE OF SEQUENCE {
                       operation       ENUMERATED {
                                               add     (0),
                                               delete  (1),
                                               replace (2) },
                       modification    AttributeTypeAndValues } }

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

  Parameters of the Modify Request are:

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

  - modification: A list of modifications to be performed on the
    entry. The entire list of entry modifications MUST be performed in
    the order they are listed, as a single atomic operation. While
    individual modifications may violate the directory schema, the
    resulting entry after the entire list of modifications is
    performed MUST conform to the requirements of the directory

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            Lightweight Directory Access Protocol Version 3

    schema. The values that may be taken on by the 'operation' field
    in each modification construct have the following semantics
    respectively:

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

           delete: delete values listed from the given 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 given 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
                                                                  Comment
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           attribute does not exist.
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  The result of the modification attempted by the server upon receipt
  of a Modify Request is returned in a Modify Response, defined as
  follows:

       ModifyResponse ::= [APPLICATION 7] LDAPResult

  Upon receipt of a Modify Request, a server will perform the necessary
  modifications to the DIT.

  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. Note that 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 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, those values which form the entry's
  relative distinguished name. An attempt to do so will result in the
  server returning the error notAllowedOnRDN. The Modify DN Operation
  described in section 4.9 is used to rename an entry.

  If an EQUALITY matching rule has not been defined for an attribute
  type, clients MUST NOT attempt to add or delete individual values of
  that attribute from an entry using the "add" or "delete" form of a
  modification, and MUST instead use the "replace" form.

  Note that due to the simplifications made in LDAP, there is not a
  direct mapping of the modifications in an LDAP ModifyRequest onto the
  EntryModifications of a DAP ModifyEntry operation, and different
  implementations of LDAP-DAP gateways may use different means of

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            Lightweight Directory Access Protocol Version 3

  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 SEQUENCE {
               type    AttributeDescription,
               vals    SET OF AttributeValue }

  Parameters of the Add Request are:

  - entry: the Distinguished Name of the entry to be added. Note that
    the server will not dereference any aliases in locating the entry
    to be added.

  - attributes: the list of attributes that make up the content of the
    entry being added. Clients MUST include distinguished values
    (those forming the entry's own RDN) in this list, 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.

  The entry named in the entry field of the AddRequest MUST NOT exist
  for the AddRequest to succeed. The parent of the 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 error noSuchObject with the matchedDN field containing "DC=NET".
  If the parent entry exists but is not in a naming context held by the
  server, the server SHOULD return a referral to the server holding the
  parent entry.

  Servers implementations SHOULD NOT restrict where entries can be
  located in the directory unless DIT structure rules are in place.
  Some servers MAY 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 perform the
  add requested. 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 is present in the
  directory.

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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 Distinguished Name of the entry to
  be deleted. Note that the server will not dereference aliases while
  resolving the name of the target entry to be removed, and that only
  leaf entries (those with no subordinate entries) can be deleted with
  this operation.

  The result of the delete attempted by the server upon receipt of a
  Delete Request is returned in the Delete Response, defined as
  follows:

      DelResponse ::= [APPLICATION 11] LDAPResult

  Upon receipt of a Delete Request, a server will attempt to perform
  the entry removal requested. The result of the delete attempt will be
  returned to the client in the Delete Response.


4.9. Modify DN Operation

  The Modify DN Operation allows a client to change the leftmost (least
  significant) component of the name of an entry in the directory, 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,
               deleteoldrdn    BOOLEAN,
               newSuperior     [0] LDAPDN OPTIONAL }

  Parameters of the Modify DN Request are:

  - entry: the Distinguished Name of the entry to be changed. This
    entry may or may not have subordinate entries. Note that the
    server will not dereference any aliases in locating the entry to
    be changed.

  - newrdn: the RDN that will form the leftmost component of the new
    name of the entry.

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


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  - newSuperior: if present, this is the Distinguished Name of the
    entry which becomes the immediate superior of the existing entry.

  The result of the name change attempted by the server upon receipt of
  a Modify DN Request is returned in the Modify DN Response, defined as
  follows:

       ModifyDNResponse ::= [APPLICATION 13] LDAPResult

  Upon receipt of a ModifyDNRequest, a server will attempt to perform
  the name change. The result of the name change attempt will be
  returned to the client in the Modify DN Response.

  For example, if the entry named in the "entry" parameter was "cn=John
  Smith,c=US", the newrdn parameter was "cn=John Cougar Smith", and the
  newSuperior parameter 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 error
  code entryAlreadyExists.

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

  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
  resultCode affectsMultipleDSAs 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.


4.10. Compare Operation

  The Compare Operation allows a client to compare an assertion
  provided with an entry in the directory. The Compare Request is
  defined as follows:

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

  Parameters of the Compare Request are:

  - entry: the name of the entry to be compared with. Note that the
    server SHOULD NOT dereference any aliases in locating the entry to
    be compared with.

  - ava: the assertion with which an attribute in the entry is to be
    compared.


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            Lightweight Directory Access Protocol Version 3

  The result of the compare attempted by the server upon receipt of a
  Compare Request is returned in the Compare Response, defined as
  follows:

       CompareResponse ::= [APPLICATION 15] LDAPResult

  Upon receipt of a Compare Request, a server will attempt to perform
  the requested comparison using the EQUALITY matching rule for the
  attribute type. The result of the comparison will be returned to the
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  client in the Compare Response. Note that errors and the result of
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  comparison are all returned in the same construct.
                                                                  i
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  Note that some directory systems may establish access controls which
  permit the values of certain attributes (such as userPassword) to be
  compared but not read.


4.11. Abandon Operation

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

       AbandonRequest ::= [APPLICATION 16] MessageID

  The MessageID MUST be that of an operation which was requested
  earlier in this connection. 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
  transmission of an Abandon Operation, the server MAY abandon the
  operation identified by the Message ID in the Abandon Request.
  Operation responses are not sent for successfully abandoned
  operations. Clients can determine that an operation has been
  abandoned by performing a subsequent bind operation.

  Abandon and Unbind operations cannot be abandoned. The ability to
  abandon other (particularly update) operations is at the discretion
  of the server.

  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.

  Clients MUST 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).


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            Lightweight Directory Access Protocol Version 3

  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

  An extension mechanism has been added in this version of LDAP, in
  order to allow additional operations to be defined for services not
  available elsewhere in this protocol, for instance digitally signed
  operations and results.

  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
  request MUST have a unique OBJECT IDENTIFIER assigned to it.

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

  The requestName is a dotted-decimal representation of the OBJECT
  IDENTIFIER corresponding to the request. The requestValue is
  information in a form defined by that request, encapsulated inside an
  OCTET STRING.

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

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

  If the server does not recognize the request name, it MUST return
  only the response fields from LDAPResult, containing the
  protocolError result code.


5. Protocol Element Encodings and Transfer

  One underlying service is defined here. Clients and servers SHOULD
  implement the mapping of LDAP over TCP described in 5.2.1.


5.1. Protocol Encoding

  The protocol elements of LDAP are encoded for exchange using the
  Basic Encoding Rules (BER) [X.690] of ASN.1 [X.680]. However, due to
  the high overhead involved in using certain elements of the BER, the
  following additional restrictions are placed on BER-encodings of LDAP
  protocol elements:

  (1) Only the definite form of length encoding will be used.

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            Lightweight Directory Access Protocol Version 3


  (2) OCTET STRING values will be encoded in the primitive form only.

  (3) If the value of a BOOLEAN type is true, the encoding MUST have
      its contents octets set to hex "FF".

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

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

  This protocol is designed to run over connection-oriented, reliable
  transports, with all 8 bits in an octet being significant in the data
  stream.


5.2.1. Transmission Control Protocol (TCP)

  The encoded LDAPMessage PDUs are mapped directly onto the TCP
  bytestream using the BER-based encoding described in section 5.1. It
  is recommended that server implementations running over the TCP
  provide a protocol listener on the assigned port, 389. Servers may
  instead provide a listener on a different port number. Clients MUST
  support contacting servers on any valid TCP port.


6. Implementation Guidelines

  This document describes an Internet protocol.


6.1. Server Implementations

  The server MUST be capable of recognizing all the mandatory attribute
  type names and implement the syntaxes specified in [Syntaxes].
  Servers MAY also recognize additional attribute type names.


6.2. Client Implementations

  Clients which request 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 clients may be using a counter that is incremented each time
  referral handling occurs for an operation, and these kinds of clients
  MUST be able to handle a DIT with at least ten layers of naming
  contexts between the root and a leaf entry.


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  In the absence of prior agreements with servers, clients SHOULD NOT
  assume that servers support any particular schemas beyond those
  referenced in section 6.1. Different schemas can have different
  attribute types with the same names. The client can retrieve the
  subschema entries referenced by the subschemaSubentry attribute in
  the server's root DSE or in entries held by the server.


7. Security Considerations

  When used with a connection-oriented transport, this version of the
  protocol provides facilities for simple authentication using a
  cleartext password, as well as any SASL mechanism [RFC2222]. SASL
  allows for integrity and privacy services to be negotiated.

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

  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.

  When used with SASL, it should be noted that the name field of the
  BindRequest is not protected against modification. Thus if the
  distinguished name of the client (an LDAPDN) is agreed through the
  negotiation of the credentials, it takes precedence over any value in
  the unprotected name field.

  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.


8. Acknowledgements

  This document is an update to RFC 2251, by Mark Wahl, Tim Howes, and
  Steve Kille. Their work along with the input of individuals of the
  IETF LDAPEXT, LDUP, LDAPBIS, and other Working Groups is gratefully
  acknowledged.


9. Normative References

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

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


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            Lightweight Directory Access Protocol Version 3

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

  [X.680]   ITU-T Recommendation X.680 (1997) | ISO/IEC 8824-1:1998
           Information Technology - Abstract Syntax Notation One
           (ASN.1): Specification of basic notation

  [X.690]   ITU-T Rec. X.690, "Specification of ASN.1 encoding rules:
           Basic, Canonical, and Distinguished Encoding Rules", 1994.

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

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

  [RFC2044] Yergeau, F., "UTF-8, a transformation format of Unicode
           and ISO 10646", RFC 2044, October 1996.

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

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

  [Syntaxes] K. Dally (editor), "LDAP: Syntaxes", draft-ietf-ldapbis-
           syntaxes-xx.txt, (a work in progress).

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

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

  [RFC2396] Berners-Lee, T., Fielding, R., and L. Masinter Uniform
           Resource Identifiers (URI): Generic Syntax", RFC 2396,
           August 1998.

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

  [RFC2222] Meyers, J., "Simple Authentication and Security Layer",
           RFC 2222, October 1997.


10. 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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            Lightweight Directory Access Protocol Version 3

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 4.1.10.

  Additional result codes MAY be defined for use with extensions.
  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),
      compareTrue(6),
      compareFalse(7),
      referral(10), and
      saslBindInProgress(14).

  The success(0), compareTrue(6), and compare(7) result codes indicate
  successful completion (and, hence, are called to as "successful"
  result codes).

  The referral(10) and saslBindInProgress(14) indicate the client is
  required to take additional action to complete the operation


A.2 Error Result Codes

A.3 Classes and Precedence of Error Result Codes

  Result codes that indicate error conditions (and, hence, are called
  "error" result codes) fall into 6 classes. The following list
  specifies the precedence of error classes to be used when more than
  one error is detected [X511]:
      1) Name Errors (codes 32 - 34, 36)
             - a problem related to a name (DN or RDN),
      2) Update Errors (codes 64 - 69, 71)
             - a problem related to an update operation,
      3) Attribute Errors (codes 16 - 21)
             - a problem related to a supplied attribute,
      4) Security Errors (codes 8, 13, 48 - 50)
             - a security related problem,
      5) Service Problem (codes 3, 4, 7, 11, 12, 51 - 54, 80)
             - a problem related to the provision of the service, and
      6) Protocol Problem (codes 1, 2)
             - a problem related to protocol structure or semantics.

  Server implementations SHALL NOT continue processing an operation
  after it has determined that an error is to be reported. If the
  server detects multiple errors simultaneously, the server SHOULD
  report the error with the highest precedence.

  Existing LDAP result codes are described as follows:

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      success (0)

         Indicates successful completion of an operation.

         This result code is normally not returned by 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
         Start TLS [RFC2830] while there are other operations
         outstanding or if TLS was already established.

         For the bind operation only, the code indicates the server
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         encountered an internal error.
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      protocolError (2)

         Indicates the server received data which has incorrect
         structure.

         For bind operation only, the code may be resulted to indicate
                                                                  Comment
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         the server does not support the requested protocol version.
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      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 operation successfully completes and the
         assertion has evaluated to TRUE.

         This result code is normally only returned by the compare
         operation.


      compareTrue (6)


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            Lightweight Directory Access Protocol Version 3

         Indicates that the operation successfully completes and the
         assertion has evaluated to FALSE.

         This result code is normally only returned by the compare
         operation.


      authMethodNotSupported (7)

         Indicates that authentication method or mechanism is not
         supported.


      strongAuthRequired (8)

         Except when returned in a Notice of Disconnect (see section
         4.4.1), this indicates that the server requires the client to
         authentication using a strong(er) mechanism.


      referral (10)

         Indicates that a referral needs to be chased to complete the
         operation (see section 4.1.11).


      adminLimitExceeded (11)

         Indicates that an admnistrative limit has been exceeded.


      unavailableCriticalExtension (12)

         Indicates that server cannot perform a critical extension
         (see section 4.1.12).


      confidentialityRequired (13)

         Indicates that data confidentiality protections are required.


      saslBindInProgress (14)

         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.


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      undefinedAttributeType (17)

         Indicates that a request field contains an undefined
         attribute type.


      inappropriateMatching (18)

         Indicates that a request cannot be completed due to an
         inappropriate matching.


      constraintViolation (19)

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

         For example, this code is returned when the 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 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.


      invalidDNSyntax (34)

         Indicates that a 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.


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      aliasDereferencingProblem (36)

         Indicates that a problem in dereferencing an alias.


      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 the supplied credentials 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 busy.


      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.


      namingViolation (64)

         Indicates that the entry name violates naming restrictions.

      objectClassViolation (65)

         Indicates that the entry violates object class restrictions.


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      notAllowedOnNonLeaf (66)

         Indicates that 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 added fulfilled as the
         entry already exists.


      objectClassModsProhibited (69)

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

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


      affectsMultipleDSAs (71)

         Indicates that the operation cannot be completed as it
         affects 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 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,
                  ... },
                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

       RelativeLDAPDN ::= LDAPString

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

       AttributeDescriptionList ::= SEQUENCE OF

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               AttributeDescription

       AttributeValue ::= OCTET STRING

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

       AssertionValue ::= OCTET STRING

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

       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 --
                            inappropriateAuthentication  (48),
                            invalidCredentials           (49),
                            insufficientAccessRights     (50),
                            busy                         (51),
                            unavailable                  (52),
                            unwillingToPerform           (53),
                            loopDetect                   (54),
                                       -- 55-63 unused --

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                            namingViolation              (64),
                            objectClassViolation         (65),
                            notAllowedOnNonLeaf          (66),
                            notAllowedOnRDN              (67),
                            entryAlreadyExists           (68),
                            objectClassModsProhibited    (69),
                                       -- 70 reserved for CLDAP --
                            affectsMultipleDSAs          (71),
                                       -- 72-79 unused --
                            other                        (80),
                            ... },
                            -- 81-90 reserved for APIs --
               matchedDN       LDAPDN,
               errorMessage    LDAPString,
               referral        [3] Referral OPTIONAL }

       Referral ::= SEQUENCE OF LDAPURL

       LDAPURL ::= LDAPString -- limited to characters permitted in
                          -- URLs

       Controls ::= SEQUENCE OF 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 }

       UnbindRequest ::= [APPLICATION 2] NULL

       SearchRequest ::= [APPLICATION 3] SEQUENCE {
               baseObject      LDAPDN,
               scope           ENUMERATED {
                       baseObject              (0),
                       singleLevel             (1),

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                       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      AttributeDescriptionList }

       Filter ::= CHOICE {
               and             [0] SET SIZE (1..MAX) OF Filter,
               or              [1] SET SIZE (1..MAX) OF 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 OF 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 }

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

       SearchResultReference ::= [APPLICATION 19] SEQUENCE OF LDAPURL

       SearchResultDone ::= [APPLICATION 5] LDAPResult

       ModifyRequest ::= [APPLICATION 6] SEQUENCE {
               object          LDAPDN,
               modification    SEQUENCE OF SEQUENCE {

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                       operation       ENUMERATED {
                                               add     (0),
                                               delete  (1),
                                               replace (2) },
                       modification    AttributeTypeAndValues } }

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

       ModifyResponse ::= [APPLICATION 7] LDAPResult

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

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

       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,
               response         [11] OCTET STRING OPTIONAL }

       END


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Appendix C - Change History
  <Note to RFC editor: This section is to be removed prior to RFC
  publication>

C.1 Changes made to RFC 2251:

C.1.1 Editorial

  - Bibliography References: Changed all bibliography references to
    use a long name form for readability.
  - Changed occurrences of "unsupportedCriticalExtension"
    "unavailableCriticalExtension"
  - Fixed a small number of misspellings (mostly dropped letters).

C.1.2 Section 1

  - Removed IESG note.

C.1.3 Section 9

  - Added references to RFCs 1823, 2234, 2829 and 2830.


C.2 Changes made to draft-ietf-ldapbis-protocol-00.txt:

C.2.1 Section 4.1.6

  - In the first paragraph, clarified what the contents of an
    AttributeValue are. There was confusion regarding whether or not
    an AttributeValue that is BER encoded (due to the "binary" option)
    is to be wrapped in an extra OCTET STRING.
  - To the first paragraph, added wording that doesn't restrict other
    transfer encoding specifiers from being used. The previous wording
    only allowed for the string encoding and the ;binary encoding.
  - To the first paragraph, added a statement restricting multiple
    options that specify transfer encoding from being present. This
    was never specified in the previous version and was seen as a
    potential interoperability problem.
  - Added a third paragraph stating that the ;binary option is
    currently the only option defined that specifies the transfer
    encoding. This is for completeness.

C.2.2 Section 4.1.7

  - Generalized the second paragraph to read "If an option specifying
    the transfer encoding is present in attributeDesc, the
    AssertionValue is encoded as specified by the option...".
    Previously, only the ;binary option was mentioned.

C.2.3 Sections 4.2, 4.9, 4.10

  - Added alias dereferencing specifications. In the case of modDN,
    followed precedent set on other update operations (... alias is
    not dereferenced...) In the case of bind and compare stated that

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    servers SHOULD NOT dereference aliases. Specifications were added
    because they were missing from the previous version and caused
    interoperability problems. Concessions were made for bind and
    compare (neither should have ever allowed alias dereferencing) by
    using SHOULD NOT language, due to the behavior of some existing
    implementations.

C.2.4 Sections 4.5 and Appendix A

  - Changed SubstringFilter.substrings.initial, any, and all from
    LDAPString to AssertionValue. This was causing an incompatibility
    with X.500 and confusion among other TS RFCs.


C.3 Changes made to draft-ietf-ldapbis-protocol-01.txt:

C.3.1 Section 3.4

  - Reworded text surrounding subschemaSubentry to reflect that it is
    a single-valued attribute that holds the schema for the root DSE.
    Also noted that if the server masters entries that use differing
    schema, each entry's subschemaSubentry attribute must be
    interrogated. This may change as further fine-tuning is done to
    the data model.

C.3.2 Section 4.1.12

  - Specified that the criticality field is only used for requests and
    not for unbind or abandon. Noted that it is ignored for all other
    operations.

C.3.3 Section 4.2

  - Noted that Server behavior is undefined when the name is a null
    value, simple authentication is used, and a password is specified.

C.3.4 Section 4.2.(various)

  - Changed "unauthenticated" to "anonymous" and "DN" and "LDAPDN" to
    "name"

C.3.5 Section 4.2.2

  - Changed "there is no authentication or encryption being performed
    by a lower layer" to "the underlying transport service cannot
    guarantee confidentiality"

C.3.6 Section 4.5.2

  - Removed all mention of ExtendedResponse due to lack of
    implementation.

C.4 Changes made to draft-ietf-ldapbis-protocol-02.txt:


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C.4.1 Section 4

  - Removed "typically" from "and is typically transferred" in the
    first paragraph. We know of no (and can conceive of no) case where
    this isn't true.
  - Added "Section 5.1 specifies how the LDAP protocol is encoded." To
    the first paragraph. Added this cross reference for readability.
  - Changed "version 3 " to "version 3 or later" in the second
    paragraph. This was added to clarify the original intent.
  - Changed "protocol version" to "protocol versions" in the third
    paragraph. This attribute is multi-valued with the intent of
    holding all supported versions, not just one.

C.4.2 Section 4.1.8

  - Changed "when transferred in protocol" to "when transferred from
    the server to the client" in the first paragraph. This is to
    clarify that this behavior only happens when attributes are being
    sent from the server.

C.4.3 Section 4.1.10

  - Changed "servers will return responses containing fields of type
    LDAPResult" to "servers will return responses of LDAPResult or
    responses containing the components of LDAPResponse". This
    statement was incorrect and at odds with the ASN.1. The fix here
    reflects the original intent.
  - Dropped '--new' from result codes ASN.1. This simplification in
    comments just reduces unneeded verbiage.

C.4.4 Section 4.1.11

  - Changed "It contains a reference to another server (or set of
    servers)" to "It contains one or more references to one or more
    servers or services" in the first paragraph. This reflects the
    original intent and clarifies that the URL may point to non-LDAP
    services.

C.4.5 Section 4.1.12

  - 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.4.6 Section 4.4

  - Changed "One unsolicited notification is defined" to "One
    unsolicited notification (Notice of Disconnection) is defined" in
    the third paragraph. For clarity and readability.

C.4.7 Section 4.5.1


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  - Changed "checking for the existence of the objectClass attribute"
    to "checking for the presence of the objectClass attribute" in the
    last paragraph. This was done as a measure of consistency (we use
    the terms present and presence rather than exists and existence in
    search filters).

C.4.8 Section 4.5.3

  - Changed "outstanding search operations to different servers," to
    "outstanding search operations" in the fifth paragraph as they may
    be to the same server. This is a point of clarification.

C.4.9 Section 4.6

  - Changed "clients MUST NOT attempt to delete" to "clients MUST NOT
    attempt to add or delete" in the second to last paragraph.
  - Change "using the "delete" form" to "using the "add" or "delete"
    form" in the second to last paragraph.

C.4.10 Section 4.7

  - Changed "Clients MUST NOT supply the createTimestamp or
    creatorsName attributes, since these will be generated
    automatically by the server." to "Clients MUST NOT supply NO-USER-
    MODIFICATION attributes such as createTimestamp or creatorsName
    attributes, since these are provided by the server." in the
    definition of the attributes field. This tightens the language to
    reflect the original intent and to not leave a hole in which one
    could interpret the two attributes mentioned as the only non-
    writable attributes.

C.4.11 Section 4.11

  - Changed "has been" to "will be" in the fourth paragraph. This
    clarifies that the server will (not has) abandon the operation.


C.5 Changes made to draft-ietf-ldapbis-protocol-03.txt:

C.5.1 Section 3.2.1

  - Changed "An attribute is a type with one or more associated
    values. The attribute type is identified by a short descriptive
    name and an OID (object identifier). The attribute type governs
    whether there can be more than one value of an attribute of that
    type in an entry, the syntax to which the values must conform, the
    kinds of matching which can be performed on values of that
    attribute, and other functions." to " An attribute is a
    description (a type and zero or more options) with one or more
    associated values. The attribute type governs whether the
    attribute can have multiple values, the syntax and matching rules
    used to construct and compare values of that attribute, and other
    functions. Options indicate modes of transfer and other

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    functions.". This points out that an attribute consists of both
    the type and options.

C.5.2 Section 4

  -  Changed "Section 5.1 specifies the encoding rules for the LDAP
    protocol" to "Section 5.1 specifies how the protocol is encoded
    and transferred."

C.5.3 Section 4.1.2

  - Added ABNF for the textual representation of LDAPOID. Previously,
    there was no formal BNF for this construct.

C.5.4 Section 4.1.4

  - Changed "This identifier may be written as decimal digits with
    components separated by periods, e.g. "2.5.4.10"" to "may be
    written as defined by ldapOID in section 4.1.2" in the second
    paragraph. This was done because we now have a formal BNF
    definition of an oid.

C.5.5 Section 4.1.5

  - Changed the BNF for AttributeDescription to ABNF. This was done
    for readability and consistency (no functional changes involved).
  - Changed "Options present in an AttributeDescription are never
    mutually exclusive." to "Options MAY be mutually exclusive. An
    AttributeDescription with mutually exclusive options is treated as
    an undefined attribute type." for clarity. It is generally
    understood that this is the original intent, but the wording could
    be easily misinterpreted.
  - Changed "Any option could be associated with any AttributeType,
    although not all combinations may be supported by a server." to
    "Though any option or set of options could be associated with any
    AttributeType, the server support for certain combinations may be
    restricted by attribute type, syntaxes, or other factors.". This
    is to clarify the meaning of 'combination' (it applies both to
    combination of attribute type and options, and combination of
    options). It also gives examples of *why* they might be
    unsupported.

C.5.6 Section 4.1.11

  - Changed the wording regarding 'equally capable' referrals to "If
    multiple URLs are present, the client assumes that any URL may be
    used to progress the operation.". The previous language implied
    that the server MUST enforce rules that it was practically
    incapable of. The new language highlights the original intent--
    that is, that any of the referrals may be used to progress the
    operation, there is no inherent 'weighting' mechanism.

C.5.7 Section 4.5.1 and Appendix A


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  - Added the comment "-- initial and final can occur at most once",
    to clarify this restriction.

C.5.8 Section 5.1

  - Changed heading from "Mapping Onto BER-based Transport Services"
    to "Protocol Encoding".

C.5.9 Section 5.2.1

  - Changed "The LDAPMessage PDUs" to "The encoded LDAPMessage PDUs"
    to point out that the PDUs are encoded before being streamed to
    TCP.

C.6 Changes made to draft-ietf-ldapbis-protocol-04.txt:

C.6.1 Section 4.5.1 and Appendix A

  - Changed the ASN.1 for the and and or choices of Filter to have a
    lower range of 1. This was an omission in the original ASN.1

C.6.2 Various

  - Fixed various typo's

C.7 Changes made to draft-ietf-ldapbis-protocol-05.txt:

C.7.1 Section 3.2.1

  - Added "(as defined in Section 12.4.1 of [X.501])" to the fifth
    paragraph when talking about "operational attributes". This is
    because the term "operational attributes" is never defined.
    Alternately, we could drag a definition into the spec, for now,
    I'm just pointing to the reference in X.501.

C.7.2 Section 4.1.5

  - Changed "And is also case insensitive" to "The entire
    AttributeDescription is case insensitive". This is to clarify
    whether we're talking about the entire attribute description, or
    just the options.

  - Expounded on the definition of attribute description options. This
    doc now specifies a difference between transfer and tagging
    options and describes the semantics of each, and how and when
    subtyping rules apply. Now allow options to be transmitted in any
    order but disallow any ordering semantics to be implied. These
    changes are the result of ongoing input from an engineering team
    designed to deal with ambiguity issues surrounding attribute
    options.

C.7.3 Sections 4.1.5.1 and 4.1.6


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  - Refer to non "binary" transfer encodings as "native encoding"
    rather than "string" encoding to clarify and avoid confusion.

C.8 Changes made to draft-ietf-ldapbis-protocol-06.txt:

C.8.1 Title

  - Changed to "LDAP: The Protocol" to be consisted with other working
    group documents

C.8.2 Abstract

  - Moved above TOC to conform to new guidelines

  - Reworded to make consistent with other WG documents.

  - Moved 2119 conventions to "Conventions" section

C.8.3 Introduction

  - Created to conform to new guidelines

C.8.4 Models

  - Removed section. There is only one model in this document
    (Protocol Model)

C.8.5 Protocol Model

  - Removed antiquated paragraph: "In keeping with the goal of easing
    the costs associated with use of the directory, it is an objective
    of this protocol to minimize the complexity of clients so as to
    facilitate widespread deployment of applications capable of using
    the directory."

  - Removed antiquated paragraph concerning LDAP v1 and v2 and
    referrals.

C.8.6 Data Model

  - Removed Section 3.2 and subsections. These have been moved to
    [Models]

C.8.7 Relationship to X.500

  - Removed section. It has been moved to [Roadmap]

C.8.8 Server Specific Data Requirements

  - Removed section. It has been moved to [Models]

C.8.9 Elements of Protocol


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  - Added "Section 5.1 specifies how the protocol is encoded and
    transferred." to the end of the first paragraph for reference.

  - Reworded notes about extensibility, and now talk about implied
    extensibility and the use of ellipses in the ASN.1

  - Removed references to LDAPv2 in third and fourth paragraphs.

C.8.10 Message ID

  - Reworded second paragraph to "The message ID of a request MUST
    have a non-zero value different from the values of any other
    requests outstanding in the LDAP session of which this message is
    a part. The zero value is reserved for the unsolicited
    notification message." (Added notes about non-zero and the zero
    value).

C.8.11 String Types

  - Removed ABNF for LDAPOID and added "Although an LDAPOID is encoded
    as an OCTET STRING, values are limited to the definition of
    numericoid given in Section 1.3 of [Models]."

C.8.12 Distinguished Name and Relative Distinguished Name

  - Removed ABNF and referred to [Models] and [LDAPDN] where this is
    defined.

C.8.13 Attribute Type

  - Removed sections. It's now in the [Models] doc.

C.8.14 Attribute Description

  - Removed ABNF and aligned section with [Models]

  - Moved AttributeDescriptionList here.

C.8.15 Transfer Options

  - Added section and consumed much of old options language (while
    aligning with [Models]

C.8.16 Binary Transfer Option

  - Clarified intent regarding exactly what is to be BER encoded.

  - Clarified that clients must not expect ;binary when not asking for
    it (;binary, as opposed to ber encoded data).


C.8.17 Attribute

  - Use the term "attribute description" in lieu of "type"

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  - Clarified the fact that clients cannot rely on any apparent
    ordering of attribute values.

C.8.18 LDAPResult

  - To resultCode, added ellipses "..." to the enumeration to indicate
    extensibility. and added a note, pointing to [LDAPIANA]

  - Removed error groupings ad refer to Appendix A.

C.8.19 Bind Operation

  - Added "Prior to the BindRequest, the implied identity is
    anonymous. Refer to [AuthMeth] for the authentication-related
    semantics of this operation." to the first paragraph.

  - Added ellipses "..." to AuthenticationChoice and added a note
    "This type is extensible as defined in Section 3.6 of [LDAPIANA].
    Servers that do not support a choice supplied by a client will
    return authMethodNotSupported in the result code of the
    BindResponse."

  - Simplified text regarding how the server handles unknown versions.
    Removed references to LDAPv2

C.8.20 Sequencing of the Bind Request

  - Aligned with [AuthMeth] In particular, paragraphs 4 and 6 were
    removed, while a portion of 4 was retained (see C.8.9)

C.8.21 Authentication and other Security Service

  - Section was removed. Now in [AuthMeth]

C.8.22 Continuation References in the Search Result

  - Added "If the originating search scope was singleLevel, the scope
    part of the URL will be baseObject."

C.8.23 Security Considerations

  - Removed reference to LDAPv2

C.8.24 Result Codes

  - Added as normative appendix A

C.8.25 ASN.1

  - Added EXTENSIBILITY IMPLIED

  - Added a number of comments holding referenced to [Models] and
    [ISO10646].

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  - Removed AttributeType. It is not used.


C.9 Changes made to draft-ietf-ldapbis-protocol-07.txt:

  - Removed all mention of transfer encodings and the binary attribute
    option

  - Further alignment with [Models].

  - Added extensibility ellipsis to protocol op choice

  - In 4.1.1, clarified when connections may be dropped due to
    malformed PDUs

  - Specified which matching rules and syntaxes are used for various
    filter items

C.10 Changes made to draft-ietf-ldapbis-protocol-07.txt:

C.10.1 Section 4.1.1.1:

  - Clarified when it is and isn't appropriate to return an already
    used result code.

C.10.2 Section 4.1.11:

  - Clarified that a control only applies to the message it's attached
    to.

  - Explained that the criticality field is only applicable to certain
    request messages.

  - Added language regarding the combination of controls.

C.10.3 Section 4.11:

  - Explained that Abandon and Unbind cannot be abandoned, and
    illustrated how to determine whether an operation has been
    abandoned.


Appendix D - Outstanding Work Items

D.0 Integrate notational consistency agreements
  - WG will discuss notation consistency. Once agreement happens,
    reconcile draft.

D.1 Integrate result codes draft.

  - The result codes draft should be reconciled with this draft.
    Operation-specific instructions will reside with operations while
    the error-specific sections will be added as an appendix. Note

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    that there is a result codes appendix now. Still need to reconcile
    with each operation.

D.2 Verify references.

  - Many referenced documents have changed. Ensure references and
    section numbers are correct.

D.3 Usage of Naming Context

  - Make sure occurrences of "namingcontext" and "naming context" are
    consistent with [Models].

D.14 Section 4.1.12

  - Specify whether or not servers are to advertise the OIDs of known
    response controls.


D.18 Section 4.2.3

  - Change "operationsError" to "other" as a bind result code.


D.21 Section 4.5.1

  - Make sure the use of "subordinates" in the derefInSearching
    definition is correct. See "derefInSearching" on list.

D.23 Section 4.5.3

  - Add "Similarly, a server MUST NOT return a SearchResultReference
    when the scope of the search is baseObject. If a client receives
    such a SearchResultReference it MUST interpret is as a protocol
    error and MUST NOT follow it." to the first paragraph.

  - Add "If the scope part of the LDAP URL is present, the client MUST
    use the new scope in its next request to progress the search. If
    the scope part is absent the client MUST use subtree scope to
    complete subtree searches and base scope to complete one level
    searches." to the third paragraph.

D.25 Section 4.6

  - Resolve the meaning of "and is ignored if the attribute does not
    exist". See "modify: "non-existent attribute"" on the list.

D.27 Section 4.10

  - Specify what happens when the attr is missing vs. attr isn't in
    schema. Also what happens if there's no equality matching rule.

D.30 Section 5.1


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  - Add "control and extended operation values" to last paragraph. See
    "LBER (BER Restrictions)" on list.

D.32 Section 6.1

  - Add "that are used by those attributes" to the first paragraph.
  - Add "Servers which support update operations MUST, and other
    servers SHOULD, support strong authentication mechanisms described
    in [RFC2829]." as a second paragraph.
  - Add "Servers which provide access to sensitive information MUST,
    and other servers SHOULD support privacy protections such as those
    described in [RFC2829] and [RFC2830]." as a third paragraph.

D.33 Section 7

  - Add "Servers which support update operations MUST, and other
    servers SHOULD, support strong authentication mechanisms described
    in [RFC2829]." as a fourth paragraph.
  - Add "In order to automatically follow referrals, clients may need
    to hold authentication secrets. This poses significant privacy and
    security concerns and SHOULD be avoided." as a sixth paragraph.
  - Add "This document provides a mechanism which clients may use to
    discover operational attributes. Those relying on security by
    obscurity should implement appropriate access controls to
    restricts access to operational attributes per local policy." as
    an eighth paragraph.
  - Add "This document provides a mechanism which clients may use to
    discover operational attributes. Those relying on security by
    obscurity should implement appropriate access controls to
    restricts access to operational attributes per local policy." as
    an eighth paragraph.
  - Add notes regarding DoS attack found by CERT advisories.




















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