RFC2251

Network Working Group                                            M. Wahl
Request for Comments: 2251                           Critical Angle Inc.
Category: Standards Track                                       T. Howes
                                           Netscape Communications Corp.
                                                                S. Kille
                                                           Isode Limited
                                                           December 1997


               Lightweight Directory Access Protocol (v3)

1. Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1997).  All Rights Reserved.

IESG Note

   This document describes a directory access protocol that provides
   both read and update access.  Update access requires secure
   authentication, but this document does not mandate implementation of
   any satisfactory authentication mechanisms.

   In accordance with RFC 2026, section 4.4.1, this specification is
   being approved by IESG as a Proposed Standard despite this
   limitation, for the following reasons:

   a. to encourage implementation and interoperability testing of
      these protocols (with or without update access) before they
      are deployed, and

   b. to encourage deployment and use of these protocols in read-only
      applications.  (e.g. applications where LDAPv3 is used as
      a query language for directories which are updated by some
      secure mechanism other than LDAP), and

   c. to avoid delaying the advancement and deployment of other Internet
      standards-track protocols which require the ability to query, but
      not update, LDAPv3 directory servers.





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   Readers are hereby warned that until mandatory authentication
   mechanisms are standardized, clients and servers written according to
   this specification which make use of update functionality are
   UNLIKELY TO INTEROPERATE, or MAY INTEROPERATE ONLY IF AUTHENTICATION
   IS REDUCED TO AN UNACCEPTABLY WEAK LEVEL.

   Implementors are hereby discouraged from deploying LDAPv3 clients or
   servers which implement the update functionality, until a Proposed
   Standard for mandatory authentication in LDAPv3 has been approved and
   published as an RFC.

Table of Contents

   1.  Status of this Memo ....................................  1
       Copyright Notice .......................................  1
       IESG Note ..............................................  1
   2.  Abstract ...............................................  3
   3.  Models .................................................  4
   3.1. Protocol Model ........................................  4
   3.2. Data Model ............................................  5
   3.2.1. Attributes of Entries ...............................  5
   3.2.2. Subschema Entries and Subentries ....................  7
   3.3. Relationship to X.500 .................................  8
   3.4. Server-specific Data Requirements .....................  8
   4.  Elements of Protocol ...................................  9
   4.1. Common Elements .......................................  9
   4.1.1. Message Envelope ....................................  9
   4.1.1.1. Message ID ........................................ 11
   4.1.2. String Types ........................................ 11
   4.1.3. Distinguished Name and Relative Distinguished Name .. 11
   4.1.4. Attribute Type ...................................... 12
   4.1.5. Attribute Description ............................... 13
   4.1.5.1. Binary Option ..................................... 14
   4.1.6. Attribute Value ..................................... 14
   4.1.7. Attribute Value Assertion ........................... 15
   4.1.8. Attribute ........................................... 15
   4.1.9. Matching Rule Identifier ............................ 15
   4.1.10. Result Message ..................................... 16
   4.1.11. Referral ........................................... 18
   4.1.12. Controls ........................................... 19
   4.2. Bind Operation ........................................ 20
   4.2.1. Sequencing of the Bind Request ...................... 21
   4.2.2. Authentication and Other Security Services .......... 22
   4.2.3. Bind Response ....................................... 23
   4.3. Unbind Operation ...................................... 24
   4.4. Unsolicited Notification .............................. 24
   4.4.1. Notice of Disconnection ............................. 24
   4.5. Search Operation ...................................... 25



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   4.5.1. Search Request ...................................... 25
   4.5.2. Search Result ....................................... 29
   4.5.3. Continuation References in the Search Result ........ 31
   4.5.3.1. Example ........................................... 31
   4.6. Modify Operation ...................................... 32
   4.7. Add Operation ......................................... 34
   4.8. Delete Operation ...................................... 35
   4.9. Modify DN Operation ................................... 36
   4.10. Compare Operation .................................... 37
   4.11. Abandon Operation .................................... 38
   4.12. Extended Operation ................................... 38
   5.  Protocol Element Encodings and Transfer ................ 39
   5.1. Mapping Onto BER-based Transport Services ............. 39
   5.2. Transfer Protocols .................................... 40
   5.2.1. Transmission Control Protocol (TCP) ................. 40
   6.  Implementation Guidelines .............................. 40
   6.1. Server Implementations ................................ 40
   6.2. Client Implementations ................................ 40
   7.  Security Considerations ................................ 41
   8.  Acknowledgements ....................................... 41
   9.  Bibliography ........................................... 41
   10. Authors' Addresses ..................................... 42
   Appendix A - Complete ASN.1 Definition ..................... 44
   Full Copyright Statement ................................... 50

2.  Abstract

   The protocol described in this document is designed to provide access
   to directories supporting the X.500 models, while not incurring the
   resource requirements of the X.500 Directory Access Protocol (DAP).
   This protocol is specifically targeted at management applications and
   browser applications that provide read/write interactive access to
   directories. When used with a directory supporting the X.500
   protocols, it is intended to be a complement to the X.500 DAP.

   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 RFC 2119 [10].

   Key aspects of this version of LDAP are:

   - All protocol elements of LDAPv2 (RFC 1777) are supported. The
     protocol is carried directly over TCP or other transport, bypassing
     much of the session/presentation overhead of X.500 DAP.

   - Most protocol data elements can be encoded as ordinary strings
     (e.g., Distinguished Names).




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   - Referrals to other servers may be returned.

   - SASL mechanisms may be used with LDAP to provide association
     security services.

   - Attribute values and Distinguished Names have been
     internationalized through the use of the ISO 10646 character set.

   - The protocol can be extended to support new operations, and
     controls may be used to extend existing operations.

   - Schema is published in the directory for use by clients.

3.  Models

   Interest in X.500 [1] directory technologies in the Internet has led
   to efforts to reduce the high cost of entry associated with use of
   these technologies.  This document continues the efforts to define
   directory protocol alternatives, updating the LDAP [2] protocol
   specification.

3.1. 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.

   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.

   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.

   In LDAP versions 1 and 2, no provision was made for protocol servers
   returning referrals to clients.  However, for improved performance
   and distribution this version of the protocol permits servers to
   return to clients referrals to other servers.  This allows servers to
   offload the work of contacting other servers to progress operations.



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   Note that the core protocol operations defined in this document can
   be mapped to a strict subset of the X.500(1997) directory abstract
   service, so it can be cleanly provided by the DAP.  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.

3.2. Data Model

   This section provides a brief introduction to the X.500 data model,
   as used by LDAP.

   The LDAP protocol assumes there are one or more servers which jointly
   provide access to a Directory Information Tree (DIT).  The tree is
   made up of entries.  Entries have names: one or more attribute values
   from the entry form its relative distinguished name (RDN), which MUST
   be unique among all its siblings.  The concatenation of the relative
   distinguished names of the sequence of entries from a particular
   entry to an immediate subordinate of the root of the tree forms that
   entry's Distinguished Name (DN), which is unique in the tree.  An
   example of a Distinguished Name is

   CN=Steve Kille, O=Isode Limited, C=GB

   Some servers may hold cache or shadow copies of entries, which can be
   used to answer search and comparison queries, but will return
   referrals or contact other servers if modification operations are
   requested.

   Servers which perform caching or shadowing MUST ensure that they do
   not violate any access control constraints placed on the data by the
   originating server.

   The largest collection of entries, starting at an entry that is
   mastered by a particular server, and including all its subordinates
   and their subordinates, down to the entries which are mastered by
   different servers, is termed a naming context.  The root of the DIT
   is a DSA-specific Entry (DSE) and not part of any naming context:
   each server has different attribute values in the root DSE.  (DSA is
   an X.500 term for the directory server).

3.2.1. Attributes of Entries

   Entries consist of a set of attributes.  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





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   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.

   An example of an attribute is "mail". There may be one or more values
   of this attribute, they must be IA5 (ASCII) strings, and they are
   case insensitive (e.g. "[e-mail]" will match "[e-mail]").

   Schema is the collection of attribute type definitions, object class
   definitions and other information which a server uses to determine
   how to match a filter or attribute value assertion (in a compare
   operation) against the attributes of an entry, and whether to permit
   add and modify operations.  The definition of schema for use with
   LDAP is given in [5] and [6].  Additional schema elements may be
   defined in other documents.

   Each entry MUST have an objectClass attribute.  The objectClass
   attribute specifies the object classes of an entry, which along with
   the system and user schema determine the permitted attributes of an
   entry.  Values of this attribute may be modified by clients, but the
   objectClass attribute cannot be removed.  Servers may restrict the
   modifications of this attribute to prevent the basic structural class
   of the entry from being changed (e.g. one cannot change a person into
   a country).  When creating an entry or adding an objectClass value to
   an entry, all superclasses of the named classes are implicitly added
   as well if not already present, and the client must supply values for
   any mandatory attributes of new superclasses.

   Some attributes, termed operational attributes, are used by servers
   for administering the directory system itself.  They are not returned
   in search results unless explicitly requested by name.  Attributes
   which are not operational, such as "mail", will have their schema and
   syntax constraints enforced by servers, but servers will generally
   not make use of their values.

   Servers MUST NOT permit clients to add attributes to an entry unless
   those attributes are permitted by the object class definitions, the
   schema controlling that entry (specified in the subschema - see
   below), or are operational attributes known to that server and used
   for administrative purposes.  Note that there is a particular
   objectClass 'extensibleObject' defined in [5] which permits all user
   attributes to be present in an entry.

   Entries MAY contain, among others, the following operational
   attributes, defined in [5]. These attributes are maintained
   automatically by the server and are not modifiable by clients:




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   - creatorsName: the Distinguished Name of the user who added this
     entry to the directory.

   - createTimestamp: the time this entry was added to the directory.

   - modifiersName: the Distinguished Name of the user who last modified
     this entry.

   - modifyTimestamp: the time this entry was last modified.

   - subschemaSubentry:  the Distinguished Name of the subschema entry
     (or subentry) which controls the schema for this entry.

3.2.2. Subschema Entries and Subentries

   Subschema entries are used for administering information about the
   directory schema, in particular the object classes and attribute
   types supported by directory servers.  A single subschema entry
   contains all schema definitions used by entries in a particular part
   of the directory tree.

   Servers which follow X.500(93) models SHOULD implement subschema
   using the X.500 subschema mechanisms, and so these subschemas are not
   ordinary entries.  LDAP clients SHOULD NOT assume that servers
   implement any of the other aspects of X.500 subschema.  A server
   which masters entries and permits clients to modify these entries
   MUST implement and provide access to these subschema entries, so that
   its clients may discover the attributes and object classes which are
   permitted to be present. It is strongly recommended that all other
   servers implement this as well.

   The following four attributes MUST be present in all subschema
   entries:

   - cn: this attribute MUST be used to form the RDN of the subschema
     entry.

   - objectClass: the attribute MUST have at least the values "top" and
     "subschema".

   - objectClasses: each value of this attribute specifies an object
     class known to the server.

   - attributeTypes: each value of this attribute specifies an attribute
     type known to the server.

   These are defined in [5]. Other attributes MAY be present in
   subschema entries, to reflect additional supported capabilities.



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   These include matchingRules, matchingRuleUse, dITStructureRules,
   dITContentRules, nameForms and ldapSyntaxes.

   Servers SHOULD provide the attributes createTimestamp and
   modifyTimestamp in subschema entries, in order to allow clients to
   maintain their caches of schema information.

   Clients MUST only retrieve attributes from a subschema entry by
   requesting a base object search of the entry, where the search filter
   is "(objectClass=subschema)". (This will allow LDAPv3 servers which
   gateway to X.500(93) to detect that subentry information is being
   requested.)

3.3. Relationship to X.500

   This document defines LDAP in terms of X.500 as an X.500 access
   mechanism.  An LDAP server MUST act in accordance with the
   X.500(1993) series of ITU recommendations when providing the service.
   However, it is not required that an LDAP server make use of any X.500
   protocols in providing this service, e.g. LDAP can be mapped onto any
   other directory system so long as the X.500 data and service model as
   used in LDAP is not violated in the LDAP interface.

3.4. Server-specific Data Requirements

   An LDAP server MUST provide information about itself and other
   information that is specific to each server.  This is represented as
   a group of attributes located in the root DSE (DSA-Specific Entry),
   which is named with the zero-length LDAPDN.  These attributes are
   retrievable if a client performs a base object search of the root
   with filter "(objectClass=*)", however they are subject to access
   control restrictions.  The root DSE MUST NOT be included if the
   client performs a subtree search starting from the root.

   Servers may allow clients to modify these attributes.

   The following attributes of the root DSE are defined in section 5 of
   [5].  Additional attributes may be defined in other documents.

   - namingContexts: naming contexts held in the server. Naming contexts
     are defined in section 17 of X.501 [6].

   - subschemaSubentry: subschema entries (or subentries) known by this
     server.

   - altServer: alternative servers in case this one is later
     unavailable.




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   - supportedExtension: list of supported extended operations.

   - supportedControl: list of supported controls.

   - supportedSASLMechanisms: list of supported SASL security features.

   - supportedLDAPVersion: LDAP versions implemented by the server.

   If the server does not master entries and does not know the locations
   of schema information, the subschemaSubentry attribute is not present
   in the root DSE.  If the server masters directory entries under one
   or more schema rules, there may be any number of values of the
   subschemaSubentry attribute in the root DSE.

4.  Elements of Protocol

   The LDAP protocol is described using Abstract Syntax Notation 1
   (ASN.1) [3], and is typically transferred using a subset of ASN.1
   Basic Encoding Rules [11]. In order to support future extensions to
   this protocol, clients and servers MUST ignore elements of SEQUENCE
   encodings whose tags they do not recognize.

   Note that unlike X.500, each change to the LDAP protocol other than
   through the extension mechanisms will have a different version
   number.  A client will indicate the version it supports as part of
   the bind request, described in section 4.2.  If a client has not sent
   a bind, the server MUST assume that version 3 is supported in the
   client (since version 2 required that the client bind first).

   Clients may determine the protocol version a server supports by
   reading the supportedLDAPVersion attribute from the root DSE. Servers
   which implement version 3 or later versions MUST provide this
   attribute.  Servers which only implement version 2 may not 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 {



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                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) --

   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 MUST return the notice of disconnection
   described in section 4.4.1, with resultCode protocolError, and
   immediately close the connection. In other cases that the server
   cannot parse the request received by the client, the server MUST
   return an appropriate response to the request, with the resultCode
   set to protocolError.

   If the client receives a PDU from the server which cannot be parsed,
   the client may discard the PDU, or may abruptly close the connection.

   The ASN.1 type Controls is defined in section 4.1.12.




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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 value different from the
   values of any other requests outstanding in the LDAP session of which
   this message is a part.

   A client MUST NOT send a second request with the same message ID as
   an earlier request on the same connection if the client has not
   received the final response from the earlier request.  Otherwise the
   behavior is undefined.  Typical clients increment a counter for each
   request.

   A client MUST NOT reuse the message id of an abandonRequest or of the
   abandoned operation until it has received a response from the server
   for another request invoked subsequent to the abandonRequest, as the
   abandonRequest itself does not have a response.

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 ISO
   10646 [13] character set (a superset of Unicode) is used, encoded
   following the UTF-8 algorithm [14]. 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

   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.

        LDAPOID ::= OCTET STRING

   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 [4], such that



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         ::= 

         ::= 

   where  and  are as defined in [4].

        LDAPDN ::= LDAPString

        RelativeLDAPDN ::= LDAPString

   Only Attribute Types can be present in a relative distinguished name
   component; the options of Attribute Descriptions (next section) MUST
   NOT be used in specifying distinguished names.

4.1.4. Attribute Type

   An AttributeType takes on as its value the textual string associated
   with that AttributeType in its specification.

        AttributeType ::= LDAPString

   Each attribute type has a unique OBJECT IDENTIFIER which has been
   assigned to it.  This identifier may be written as decimal digits
   with components separated by periods, e.g. "2.5.4.10".

   A specification may also assign one or more textual names for an
   attribute type.  These names MUST begin with a letter, and only
   contain ASCII letters, digit characters and hyphens.  They are case
   insensitive.  (These ASCII characters are identical to ISO 10646
   characters whose UTF-8 encoding is a single byte between 0x00 and
   0x7F.)

   If the server has a textual name for an attribute type, it MUST use a
   textual name for attributes returned in search results.  The dotted-
   decimal OBJECT IDENTIFIER is only used if there is no textual name
   for an attribute type.

   Attribute type textual names are non-unique, as two different
   specifications (neither in standards track RFCs) may choose the same
   name.

   A server which masters or shadows entries SHOULD list all the
   attribute types it supports in the subschema entries, using the
   attributeTypes attribute.  Servers which support an open-ended set of
   attributes SHOULD include at least the attributeTypes value for the
   'objectClass' attribute. Clients MAY retrieve the attributeTypes
   value from subschema entries in order to obtain the OBJECT IDENTIFIER
   and other information associated with attribute types.



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   Some attribute type names which are used in this version of LDAP are
   described in [5].  Servers may implement additional attribute types.

4.1.5. Attribute Description

   An AttributeDescription is a superset of the definition of the
   AttributeType.  It has the same ASN.1 definition, but allows
   additional options to be specified.  They are also case insensitive.

        AttributeDescription ::= LDAPString

   A value of AttributeDescription is based on the following BNF:

         ::=  [ ";"  ]

          ::=  |  ";" 

           ::=  *

         ::=  ASCII-equivalent letters, numbers and hyphen

   Examples of valid AttributeDescription:

        cn
        userCertificate;binary

   One option, "binary", is defined in this document.  Additional
   options may be defined in IETF standards-track and experimental RFCs.
   Options beginning with "x-" are reserved for private experiments.
   Any option could be associated with any AttributeType, although not
   all combinations may be supported by a server.

   An AttributeDescription with one or more options is treated as a
   subtype of the attribute type without any options.  Options present
   in an AttributeDescription are never mutually exclusive.
   Implementations MUST generate the  list sorted in ascending
   order, and servers MUST treat any two AttributeDescription with the
   same AttributeType and options as equivalent.  A server will treat an
   AttributeDescription with any options it does not implement as an
   unrecognized attribute type.

   The data type "AttributeDescriptionList" describes a list of 0 or
   more attribute types.  (A list of zero elements has special
   significance in the Search request.)

        AttributeDescriptionList ::= SEQUENCE OF
                AttributeDescription




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4.1.5.1. Binary Option

   If the "binary" option is present in an AttributeDescription, it
   overrides any string-based encoding representation defined for that
   attribute in [5]. Instead the attribute is to be transferred as a
   binary value encoded using the Basic Encoding Rules [11].  The syntax
   of the binary value is an ASN.1 data type definition which is
   referenced by the "SYNTAX" part of the attribute type definition.

   The presence or absence of the "binary" option only affects the
   transfer of attribute values in protocol; servers store any
   particular attribute in a single format.  If a client requests that a
   server return an attribute in the binary format, but the server
   cannot generate that format, the server MUST treat this attribute
   type as an unrecognized attribute type.  Similarly, clients MUST NOT
   expect servers to return an attribute in binary format if the client
   requested that attribute by name without the binary option.

   This option is intended to be used with attributes whose syntax is a
   complex ASN.1 data type, and the structure of values of that type is
   needed by clients.  Examples of this kind of syntax are "Certificate"
   and "CertificateList".

4.1.6. Attribute Value

   A field of type AttributeValue takes on as its value either a string
   encoding of a AttributeValue data type, or an OCTET STRING containing
   an encoded binary value, depending on whether the "binary" option is
   present in the companion AttributeDescription to this AttributeValue.

   The definition of string encodings for different syntaxes and types
   may be found in other documents, and in particular [5].

        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 NEITHER simply 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 which are not
   valid according to the syntax defined for the attributes.




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4.1.7. 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

   If the "binary" option is present in attributeDesc, this signals to
   the server that the assertionValue is a binary encoding of the
   assertion value.

   For all the string-valued user attributes described in [5], the
   assertion value syntax is the same as the value syntax.  Clients may
   use attribute values as assertion values in compare requests and
   search filters.

   Note however that the assertion syntax may be different from the
   value syntax for other attributes or for non-equality matching rules.
   These may have an assertion syntax which contains only part of the
   value.  See section 20.2.1.8 of X.501 [6] for examples.

4.1.8. Attribute

   An attribute consists of a type and one or more values of that type.
   (Though attributes MUST have at least one value when stored, due to
   access control restrictions the set may be empty when transferred in
   protocol.  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
   order of attribute values within the vals set is undefined and
   implementation-dependent, and MUST NOT be relied upon.

4.1.9. Matching Rule Identifier

   A matching rule is a means of expressing how a server should compare
   an AssertionValue received in a search filter with an abstract data
   value.  The matching rule defines the syntax of the assertion value
   and the process to be performed in the server.



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   An X.501(1993) Matching Rule is identified in the LDAP protocol by
   the printable representation of its OBJECT IDENTIFIER, either as one
   of the strings given in [5], or as decimal digits with components
   separated by periods, 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
   information is given in section 4.4 of [5].

4.1.10. Result Message

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

        LDAPResult ::= SEQUENCE {
                resultCode      ENUMERATED {
                             success                      (0),
                             operationsError              (1),
                             protocolError                (2),
                             timeLimitExceeded            (3),
                             sizeLimitExceeded            (4),
                             compareFalse                 (5),
                             compareTrue                  (6),

                             authMethodNotSupported       (7),
                             strongAuthRequired           (8),
                                        -- 9 reserved --
                             referral                     (10),  -- new
                             adminLimitExceeded           (11),  -- new
                             unavailableCriticalExtension (12),  -- new
                             confidentialityRequired      (13),  -- new
                             saslBindInProgress           (14),  -- new
                             noSuchAttribute              (16),
                             undefinedAttributeType       (17),
                             inappropriateMatching        (18),
                             constraintViolation          (19),
                             attributeOrValueExists       (20),
                             invalidAttributeSyntax       (21),
                                        -- 22-31 unused --



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                             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), -- new
                                        -- 72-79 unused --
                             other                        (80) },
                             -- 81-90 reserved for APIs --
                matchedDN       LDAPDN,
                errorMessage    LDAPString,
                referral        [3] Referral OPTIONAL }

   All the result codes with the exception of success, compareFalse and
   compareTrue are to be treated as meaning the operation could not be
   completed in its entirety.

   Most of the result codes are based on problem indications from X.511
   error data types.  Result codes from 16 to 21 indicate an
   AttributeProblem, codes 32, 33, 34 and 36 indicate a NameProblem,
   codes 48, 49 and 50 indicate a SecurityProblem, codes 51 to 54
   indicate a ServiceProblem, and codes 64 to 69 and 71 indicates an
   UpdateProblem.

   If a client receives a result code which is not listed above, it is
   to be treated as an unknown error condition.

   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,




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   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.

   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 [8]. The matchedDN field is to be set to a zero length
   string with all other result codes.

4.1.11. Referral

   The referral error 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 a reference to
   another server (or set of servers) which 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.

   The referral is not returned for a singleLevel or wholeSubtree search
   in which the search scope spans multiple naming contexts, and several
   different servers would need to be contacted to complete the
   operation. Instead, continuation references, described in section
   4.5.3, are returned.

        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 any one of servers.  All the URLs MUST be
   equally capable of being used to progress the operation.  (The
   mechanisms for how this is achieved by multiple servers are outside
   the scope of this document.)

   URLs for servers implementing the LDAP protocol are written according
   to [9].  If an alias was dereferenced, the  part of the URL MUST
   be present, with the new target object name.  If the  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



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   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.

   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 RFC 1738 [7].

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

4.1.12. Controls

   A control is a way to specify extension information. Controls which
   are sent as part of a request apply only to that request and are not
   saved.

        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.

   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 and the criticality
   field is TRUE, the server MUST NOT perform the operation, and MUST
   instead return the resultCode unsupportedCriticalExtension.

   If the control is not appropriate for the operation and criticality
   field is TRUE, the server MUST NOT perform the operation, and MUST
   instead return the resultCode unsupportedCriticalExtension.

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





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   The controlValue contains any information associated with the
   control, and its format is defined for the control.  The server 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 define any controls.  Controls may be defined
   in other documents.  The definition of a control consists of:

     - the OBJECT IDENTIFIER assigned to the control,

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

     - the format of the controlValue contents of the control.

   Servers list the controls which they recognize in the
   supportedControl attribute in the root DSE.

4.2. Bind Operation

   The function of the Bind Operation is to allow authentication
   information to be exchanged between the client and server.

   The Bind 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 version it desires.
     If the client requests protocol version 2, a server that supports
     the version 2 protocol as described in [2] will not return any v3-



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     specific protocol fields.  (Note that not all LDAP servers will
     support protocol version 2, since they may be unable to generate
     the attribute syntaxes associated with version 2.)

   - 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 LDAPDN in the credentials.

   - authentication: information used to authenticate the name, if any,
     provided in the Bind Request.

   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.

   Unlike LDAP v2, the client need not send a Bind Request in the first
   PDU of the connection.  The client may request any operations and the
   server MUST treat these as unauthenticated. If the server requires
   that the client bind before browsing or modifying the directory, the
   server MAY reject a request other than binding, unbinding or an
   extended request with the "operationsError" result.




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

   Clients MAY send multiple bind requests on a connection to change
   their credentials.  A subsequent bind process has the effect of
   abandoning all operations outstanding on the connection.  (This
   simplifies server implementation.)  Authentication from earlier binds
   are subsequently ignored, and so if the bind fails, the connection
   will be treated as anonymous. If a SASL transfer encryption or
   integrity mechanism has been negotiated, and that mechanism does not
   support the changing of credentials from one identity to another,
   then the client MUST instead establish a new connection.

4.2.2. Authentication and Other Security Services

   The simple authentication option provides minimal authentication
   facilities, with the contents of the authentication field consisting
   only of a cleartext password.  Note that the use of cleartext
   passwords is not recommended over open networks when there is no
   authentication or encryption being performed by a lower layer; see
   the "Security Considerations" section.

   If no authentication is to be performed, then the simple
   authentication option MUST be chosen, and the password be of zero
   length.  (This is often done by LDAPv2 clients.)  Typically the DN is
   also of zero length.

   The sasl choice allows for any mechanism defined for use with SASL
   [12].  The mechanism field contains the name of the mechanism.  The
   credentials field contains the arbitrary data used for
   authentication, inside an OCTET STRING wrapper.  Note that unlike
   some Internet application protocols where SASL is used, LDAP is not
   text-based, thus no base64 transformations are performed on the
   credentials.

   If any SASL-based integrity or confidentiality services are enabled,
   they take effect following the transmission by the server and
   reception by the client of the final BindResponse with resultCode
   success.

   The client can request that the server use authentication information
   from a lower layer protocol by using the SASL EXTERNAL mechanism.





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4.2.3. 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 he
   status of the client's request for authentication.

   f the bind was successful, the resultCode will be success, therwise
   it will be one of:

   - 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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   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 password 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 may assume that the protocol session
   is terminated. Upon receipt of an UnbindRequest, a protocol server
   may assume that the requesting client has terminated the session and
   that all outstanding requests may be discarded, and may 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 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





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   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.

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

   The following resultCode values are to be used in this notification:

   - 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),



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                        derefAlways             (3) },
                sizeLimit       INTEGER (0 .. maxInt),
                timeLimit       INTEGER (0 .. maxInt),
                typesOnly       BOOLEAN,
                filter          Filter,
                attributes      AttributeDescriptionList }

        Filter ::= CHOICE {
                and             [0] SET OF Filter,
                or              [1] SET 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
                substrings      SEQUENCE OF CHOICE {
                        initial [0] LDAPString,
                        any     [1] LDAPString,
                        final   [2] LDAPString } }

        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;



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             derefInSearching: dereference aliases in subordinates of
             the base object in searching, but not in locating the
             base object of the search;

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

             derefAlways: dereference aliases both in searching and in
             locating the base object of the search.

   - sizelimit: A sizelimit that restricts the maximum number of entries
     to be returned as a result of the search. A value of 0 in this
     field indicates that no client-requested sizelimit restrictions are
     in effect for the search.  Servers may enforce a maximum number of
     entries to return.

   - timelimit: A timelimit that restricts the maximum time (in seconds)
     allowed for a search. A value of 0 in this field indicates that no
     client-requested timelimit 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(93) 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.






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     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 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.






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     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
     [8].

   - 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 all user
     attributes are to be returned.  (The "*" allows the client to
     request all user attributes in addition to specific 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 control 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 [5].)

   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 existence 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 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,
   ExtendedResponse or SearchResultDone data types.

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



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                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
        -- 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 returned in binary format (indicated
   by the AttributeDescription in the response having the binary option
   present).

   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 MUST NOT assume that all attributes
   can be modified, even if permitted by access control.

   LDAPMessage responses of the ExtendedResponse form are reserved for
   returning information associated with a control requested by the
   client.  These may be defined in future versions of this document.



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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, 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.

   The SearchResultReference is of the same data type as the Referral.
   URLs for servers implementing the LDAP protocol are written according
   to [9].  The  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.  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.

   The name of an unexplored subtree in a SearchResultReference need not
   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 to
   different servers, it MUST abandon each operation individually.

4.5.3.1. Example

   For example, suppose the contacted server (hosta) holds the entry
   "O=MNN,C=WW" and the entry "CN=Manager,O=MNN,C=WW".  It knows that
   either LDAP-capable servers (hostb) or (hostc) hold
   "OU=People,O=MNN,C=WW" (one is the master and the other server a




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   shadow), and that LDAP-capable server (hostd) holds the subtree
   "OU=Roles,O=MNN,C=WW".  If a subtree search of "O=MNN,C=WW" is
   requested to the contacted server, it may return the following:

     SearchResultEntry for O=MNN,C=WW
     SearchResultEntry for CN=Manager,O=MNN,C=WW
     SearchResultReference {
       ldap://hostb/OU=People,O=MNN,C=WW
       ldap://hostc/OU=People,O=MNN,C=WW
     }
     SearchResultReference {
       ldap://hostd/OU=Roles,O=MNN,C=WW
     }
     SearchResultDone (success)

   Client implementors should note that when following a
   SearchResultReference, additional SearchResultReference may be
   generated.  Continuing the example, if the client contacted the
   server (hostb) and issued the search for the subtree
   "OU=People,O=MNN,C=WW", the server might respond as follows:

     SearchResultEntry for OU=People,O=MNN,C=WW
     SearchResultReference {
      ldap://hoste/OU=Managers,OU=People,O=MNN,C=WW
     }
     SearchResultReference {
      ldap://hostf/OU=Consultants,OU=People,O=MNN,C=WW
     }
     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 "O=XYZ,C=US" 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 {



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                        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 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
             attribute does not exist.

   The result of the modify 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.





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   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 match filter has not been defined for an attribute type,
   clients MUST NOT attempt to delete individual values of that attribute
   from an entry using the "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
   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.




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   - 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 the createTimestamp or
     creatorsName attributes, since these will be generated
     automatically by the server.

   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,O=Foo,C=US", the "O=Foo,C=US" entry did not exist, and the
   "C=US" entry did exist, then the server would return the error
   noSuchObject with the matchedDN field containing "C=US".  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.  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.

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:



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        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.

   - 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.

   - 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




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   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.

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

   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. The result of the comparison will be
   returned to the client in the Compare Response. Note that errors and
   the result of comparison are all returned in the same construct.





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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.  In a search result, it may be that an
   attribute of that type would be returned, but with an empty set of
   values.

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

   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).

   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.






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   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. Mapping Onto BER-based Transport Services

   The protocol elements of LDAP are encoded for exchange using the
   Basic Encoding Rules (BER) [11] of ASN.1 [3]. 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.

   (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".






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   (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
   noted.

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 LDAPMessage PDUs are mapped directly onto the TCP bytestream.  It
   is recommended that server implementations running over the TCP MAY
   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 [5].  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.

   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.



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7.  Security Considerations

   When used with a connection-oriented transport, this version of the
   protocol provides facilities for the LDAP v2 authentication
   mechanism, simple authentication using a cleartext password, as well
   as any SASL mechanism [12].  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 cache.

8.  Acknowledgements

   This document is an update to RFC 1777, by Wengyik Yeong, Tim Howes,
   and Steve Kille.  Design ideas included in this document are based on
   those discussed in ASID and other IETF Working Groups.  The
   contributions of individuals in these working groups is gratefully
   acknowledged.

9.  Bibliography

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

   [2] Yeong, W., Howes, T., and S. Kille, "Lightweight Directory Access
       Protocol", RFC 1777, March 1995.

   [3] ITU-T Rec. X.680, "Abstract Syntax Notation One (ASN.1) -
       Specification of Basic Notation", 1994.




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   [4] Kille, S., Wahl, M., and T. Howes, "Lightweight Directory Access
       Protocol (v3): UTF-8 String Representation of Distinguished
       Names", RFC 2253, December 1997.

   [5] Wahl, M., Coulbeck, A., Howes, T., and S. Kille, "Lightweight
       Directory Access Protocol (v3): Attribute Syntax Definitions",
       RFC 2252, December 1997.

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

   [7] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
       Resource  Locators (URL)", RFC 1738, December 1994.

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

   [9] Howes, T., and M. Smith, "The LDAP URL Format", RFC 2255,
       December 1997.

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

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

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

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

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

10. Authors' Addresses

   Mark Wahl
   Critical Angle Inc.
   4815 W Braker Lane #502-385
   Austin, TX 78759
   USA

   Phone:  [phone]
   EMail:  [e-mail]






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   Tim Howes
   Netscape Communications Corp.
   501 E. Middlefield Rd., MS MV068
   Mountain View, CA 94043
   USA

   Phone:  [phone]
   EMail:   [e-mail]

   Steve Kille
   Isode Limited
   The Dome, The Square
   Richmond
   TW9 1DT
   UK

   Phone:  [phone]
   EMail:  [e-mail]

































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Appendix A - Complete ASN.1 Definition

        Lightweight-Directory-Access-Protocol-V3 DEFINITIONS
        IMPLICIT TAGS ::=

        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

        LDAPOID ::= OCTET STRING

        LDAPDN ::= LDAPString

        RelativeLDAPDN ::= LDAPString

        AttributeType ::= LDAPString

        AttributeDescription ::= LDAPString




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        AttributeDescriptionList ::= SEQUENCE OF
                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),  -- new
                             adminLimitExceeded           (11),  -- new
                             unavailableCriticalExtension (12),  -- new
                             confidentialityRequired      (13),  -- new
                             saslBindInProgress           (14),  -- new
                             noSuchAttribute              (16),
                             undefinedAttributeType       (17),
                             inappropriateMatching        (18),
                             constraintViolation          (19),
                             attributeOrValueExists       (20),
                             invalidAttributeSyntax       (21),
                                        -- 22-31 unused --
                             noSuchObject                 (32),
                             aliasProblem                 (33),
                             invalidDNSyntax              (34),
                             -- 35 reserved for undefined isLeaf --
                             aliasDereferencingProblem    (36),
                                        -- 37-47 unused --
                             inappropriateAuthentication  (48),



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                             invalidCredentials           (49),
                             insufficientAccessRights     (50),
                             busy                         (51),
                             unavailable                  (52),
                             unwillingToPerform           (53),
                             loopDetect                   (54),
                                        -- 55-63 unused --
                             namingViolation              (64),
                             objectClassViolation         (65),
                             notAllowedOnNonLeaf          (66),
                             notAllowedOnRDN              (67),
                             entryAlreadyExists           (68),
                             objectClassModsProhibited    (69),
                                        -- 70 reserved for CLDAP --
                             affectsMultipleDSAs          (71), -- new
                                        -- 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 {



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             COMPONENTS OF LDAPResult,
             serverSaslCreds    [7] OCTET STRING OPTIONAL }

        UnbindRequest ::= [APPLICATION 2] NULL

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

        Filter ::= CHOICE {
                and             [0] SET OF Filter,
                or              [1] SET 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
                substrings      SEQUENCE OF CHOICE {
                        initial [0] LDAPString,
                        any     [1] LDAPString,
                        final   [2] LDAPString } }

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




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        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 {
                        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



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        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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Full Copyright Statement

   Copyright (C) The Internet Society (1997).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
























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Network Working Group                                            M. Wahl
Request for Comments: 2251                           Critical Angle Inc.
Category: Standards Track                                       T. Howes
                                           Netscape Communications Corp.
                                                                S. Kille
                                                           Isode Limited
                                                           December 1997


               Lightweight Directory Access Protocol (v3)

1. Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1997).  All Rights Reserved.

IESG Note

   This document describes a directory access protocol that provides
   both read and update access.  Update access requires secure
   authentication, but this document does not mandate implementation of
   any satisfactory authentication mechanisms.

   In accordance with RFC 2026, section 4.4.1, this specification is
   being approved by IESG as a Proposed Standard despite this
   limitation, for the following reasons:

   a. to encourage implementation and interoperability testing of
      these protocols (with or without update access) before they
      are deployed, and

   b. to encourage deployment and use of these protocols in read-only
      applications.  (e.g. applications where LDAPv3 is used as
      a query language for directories which are updated by some
      secure mechanism other than LDAP), and

   c. to avoid delaying the advancement and deployment of other Internet
      standards-track protocols which require the ability to query, but
      not update, LDAPv3 directory servers.





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   Readers are hereby warned that until mandatory authentication
   mechanisms are standardized, clients and servers written according to
   this specification which make use of update functionality are
   UNLIKELY TO INTEROPERATE, or MAY INTEROPERATE ONLY IF AUTHENTICATION
   IS REDUCED TO AN UNACCEPTABLY WEAK LEVEL.

   Implementors are hereby discouraged from deploying LDAPv3 clients or
   servers which implement the update functionality, until a Proposed
   Standard for mandatory authentication in LDAPv3 has been approved and
   published as an RFC.

Table of Contents

   1.  Status of this Memo ....................................  1
       Copyright Notice .......................................  1
       IESG Note ..............................................  1
   2.  Abstract ...............................................  3
   3.  Models .................................................  4
   3.1. Protocol Model ........................................  4
   3.2. Data Model ............................................  5
   3.2.1. Attributes of Entries ...............................  5
   3.2.2. Subschema Entries and Subentries ....................  7
   3.3. Relationship to X.500 .................................  8
   3.4. Server-specific Data Requirements .....................  8
   4.  Elements of Protocol ...................................  9
   4.1. Common Elements .......................................  9
   4.1.1. Message Envelope ....................................  9
   4.1.1.1. Message ID ........................................ 11
   4.1.2. String Types ........................................ 11
   4.1.3. Distinguished Name and Relative Distinguished Name .. 11
   4.1.4. Attribute Type ...................................... 12
   4.1.5. Attribute Description ............................... 13
   4.1.5.1. Binary Option ..................................... 14
   4.1.6. Attribute Value ..................................... 14
   4.1.7. Attribute Value Assertion ........................... 15
   4.1.8. Attribute ........................................... 15
   4.1.9. Matching Rule Identifier ............................ 15
   4.1.10. Result Message ..................................... 16
   4.1.11. Referral ........................................... 18
   4.1.12. Controls ........................................... 19
   4.2. Bind Operation ........................................ 20
   4.2.1. Sequencing of the Bind Request ...................... 21
   4.2.2. Authentication and Other Security Services .......... 22
   4.2.3. Bind Response ....................................... 23
   4.3. Unbind Operation ...................................... 24
   4.4. Unsolicited Notification .............................. 24
   4.4.1. Notice of Disconnection ............................. 24
   4.5. Search Operation ...................................... 25



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   4.5.1. Search Request ...................................... 25
   4.5.2. Search Result ....................................... 29
   4.5.3. Continuation References in the Search Result ........ 31
   4.5.3.1. Example ........................................... 31
   4.6. Modify Operation ...................................... 32
   4.7. Add Operation ......................................... 34
   4.8. Delete Operation ...................................... 35
   4.9. Modify DN Operation ................................... 36
   4.10. Compare Operation .................................... 37
   4.11. Abandon Operation .................................... 38
   4.12. Extended Operation ................................... 38
   5.  Protocol Element Encodings and Transfer ................ 39
   5.1. Mapping Onto BER-based Transport Services ............. 39
   5.2. Transfer Protocols .................................... 40
   5.2.1. Transmission Control Protocol (TCP) ................. 40
   6.  Implementation Guidelines .............................. 40
   6.1. Server Implementations ................................ 40
   6.2. Client Implementations ................................ 40
   7.  Security Considerations ................................ 41
   8.  Acknowledgements ....................................... 41
   9.  Bibliography ........................................... 41
   10. Authors' Addresses ..................................... 42
   Appendix A - Complete ASN.1 Definition ..................... 44
   Full Copyright Statement ................................... 50

2.  Abstract

   The protocol described in this document is designed to provide access
   to directories supporting the X.500 models, while not incurring the
   resource requirements of the X.500 Directory Access Protocol (DAP).
   This protocol is specifically targeted at management applications and
   browser applications that provide read/write interactive access to
   directories. When used with a directory supporting the X.500
   protocols, it is intended to be a complement to the X.500 DAP.

   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 RFC 2119 [10].

   Key aspects of this version of LDAP are:

   - All protocol elements of LDAPv2 (RFC 1777) are supported. The
     protocol is carried directly over TCP or other transport, bypassing
     much of the session/presentation overhead of X.500 DAP.

   - Most protocol data elements can be encoded as ordinary strings
     (e.g., Distinguished Names).




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   - Referrals to other servers may be returned.

   - SASL mechanisms may be used with LDAP to provide association
     security services.

   - Attribute values and Distinguished Names have been
     internationalized through the use of the ISO 10646 character set.

   - The protocol can be extended to support new operations, and
     controls may be used to extend existing operations.

   - Schema is published in the directory for use by clients.

3.  Models

   Interest in X.500 [1] directory technologies in the Internet has led
   to efforts to reduce the high cost of entry associated with use of
   these technologies.  This document continues the efforts to define
   directory protocol alternatives, updating the LDAP [2] protocol
   specification.

3.1. 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.

   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.

   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.

   In LDAP versions 1 and 2, no provision was made for protocol servers
   returning referrals to clients.  However, for improved performance
   and distribution this version of the protocol permits servers to
   return to clients referrals to other servers.  This allows servers to
   offload the work of contacting other servers to progress operations.



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   Note that the core protocol operations defined in this document can
   be mapped to a strict subset of the X.500(1997) directory abstract
   service, so it can be cleanly provided by the DAP.  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.

3.2. Data Model

   This section provides a brief introduction to the X.500 data model,
   as used by LDAP.

   The LDAP protocol assumes there are one or more servers which jointly
   provide access to a Directory Information Tree (DIT).  The tree is
   made up of entries.  Entries have names: one or more attribute values
   from the entry form its relative distinguished name (RDN), which MUST
   be unique among all its siblings.  The concatenation of the relative
   distinguished names of the sequence of entries from a particular
   entry to an immediate subordinate of the root of the tree forms that
   entry's Distinguished Name (DN), which is unique in the tree.  An
   example of a Distinguished Name is

   CN=Steve Kille, O=Isode Limited, C=GB

   Some servers may hold cache or shadow copies of entries, which can be
   used to answer search and comparison queries, but will return
   referrals or contact other servers if modification operations are
   requested.

   Servers which perform caching or shadowing MUST ensure that they do
   not violate any access control constraints placed on the data by the
   originating server.

   The largest collection of entries, starting at an entry that is
   mastered by a particular server, and including all its subordinates
   and their subordinates, down to the entries which are mastered by
   different servers, is termed a naming context.  The root of the DIT
   is a DSA-specific Entry (DSE) and not part of any naming context:
   each server has different attribute values in the root DSE.  (DSA is
   an X.500 term for the directory server).

3.2.1. Attributes of Entries

   Entries consist of a set of attributes.  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





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   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.

   An example of an attribute is "mail". There may be one or more values
   of this attribute, they must be IA5 (ASCII) strings, and they are
   case insensitive (e.g. "[e-mail]" will match "[e-mail]").

   Schema is the collection of attribute type definitions, object class
   definitions and other information which a server uses to determine
   how to match a filter or attribute value assertion (in a compare
   operation) against the attributes of an entry, and whether to permit
   add and modify operations.  The definition of schema for use with
   LDAP is given in [5] and [6].  Additional schema elements may be
   defined in other documents.

   Each entry MUST have an objectClass attribute.  The objectClass
   attribute specifies the object classes of an entry, which along with
   the system and user schema determine the permitted attributes of an
   entry.  Values of this attribute may be modified by clients, but the
   objectClass attribute cannot be removed.  Servers may restrict the
   modifications of this attribute to prevent the basic structural class
   of the entry from being changed (e.g. one cannot change a person into
   a country).  When creating an entry or adding an objectClass value to
   an entry, all superclasses of the named classes are implicitly added
   as well if not already present, and the client must supply values for
   any mandatory attributes of new superclasses.

   Some attributes, termed operational attributes, are used by servers
   for administering the directory system itself.  They are not returned
   in search results unless explicitly requested by name.  Attributes
   which are not operational, such as "mail", will have their schema and
   syntax constraints enforced by servers, but servers will generally
   not make use of their values.

   Servers MUST NOT permit clients to add attributes to an entry unless
   those attributes are permitted by the object class definitions, the
   schema controlling that entry (specified in the subschema - see
   below), or are operational attributes known to that server and used
   for administrative purposes.  Note that there is a particular
   objectClass 'extensibleObject' defined in [5] which permits all user
   attributes to be present in an entry.

   Entries MAY contain, among others, the following operational
   attributes, defined in [5]. These attributes are maintained
   automatically by the server and are not modifiable by clients:




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   - creatorsName: the Distinguished Name of the user who added this
     entry to the directory.

   - createTimestamp: the time this entry was added to the directory.

   - modifiersName: the Distinguished Name of the user who last modified
     this entry.

   - modifyTimestamp: the time this entry was last modified.

   - subschemaSubentry:  the Distinguished Name of the subschema entry
     (or subentry) which controls the schema for this entry.

3.2.2. Subschema Entries and Subentries

   Subschema entries are used for administering information about the
   directory schema, in particular the object classes and attribute
   types supported by directory servers.  A single subschema entry
   contains all schema definitions used by entries in a particular part
   of the directory tree.

   Servers which follow X.500(93) models SHOULD implement subschema
   using the X.500 subschema mechanisms, and so these subschemas are not
   ordinary entries.  LDAP clients SHOULD NOT assume that servers
   implement any of the other aspects of X.500 subschema.  A server
   which masters entries and permits clients to modify these entries
   MUST implement and provide access to these subschema entries, so that
   its clients may discover the attributes and object classes which are
   permitted to be present. It is strongly recommended that all other
   servers implement this as well.

   The following four attributes MUST be present in all subschema
   entries:

   - cn: this attribute MUST be used to form the RDN of the subschema
     entry.

   - objectClass: the attribute MUST have at least the values "top" and
     "subschema".

   - objectClasses: each value of this attribute specifies an object
     class known to the server.

   - attributeTypes: each value of this attribute specifies an attribute
     type known to the server.

   These are defined in [5]. Other attributes MAY be present in
   subschema entries, to reflect additional supported capabilities.



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   These include matchingRules, matchingRuleUse, dITStructureRules,
   dITContentRules, nameForms and ldapSyntaxes.

   Servers SHOULD provide the attributes createTimestamp and
   modifyTimestamp in subschema entries, in order to allow clients to
   maintain their caches of schema information.

   Clients MUST only retrieve attributes from a subschema entry by
   requesting a base object search of the entry, where the search filter
   is "(objectClass=subschema)". (This will allow LDAPv3 servers which
   gateway to X.500(93) to detect that subentry information is being
   requested.)

3.3. Relationship to X.500

   This document defines LDAP in terms of X.500 as an X.500 access
   mechanism.  An LDAP server MUST act in accordance with the
   X.500(1993) series of ITU recommendations when providing the service.
   However, it is not required that an LDAP server make use of any X.500
   protocols in providing this service, e.g. LDAP can be mapped onto any
   other directory system so long as the X.500 data and service model as
   used in LDAP is not violated in the LDAP interface.

3.4. Server-specific Data Requirements

   An LDAP server MUST provide information about itself and other
   information that is specific to each server.  This is represented as
   a group of attributes located in the root DSE (DSA-Specific Entry),
   which is named with the zero-length LDAPDN.  These attributes are
   retrievable if a client performs a base object search of the root
   with filter "(objectClass=*)", however they are subject to access
   control restrictions.  The root DSE MUST NOT be included if the
   client performs a subtree search starting from the root.

   Servers may allow clients to modify these attributes.

   The following attributes of the root DSE are defined in section 5 of
   [5].  Additional attributes may be defined in other documents.

   - namingContexts: naming contexts held in the server. Naming contexts
     are defined in section 17 of X.501 [6].

   - subschemaSubentry: subschema entries (or subentries) known by this
     server.

   - altServer: alternative servers in case this one is later
     unavailable.




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   - supportedExtension: list of supported extended operations.

   - supportedControl: list of supported controls.

   - supportedSASLMechanisms: list of supported SASL security features.

   - supportedLDAPVersion: LDAP versions implemented by the server.

   If the server does not master entries and does not know the locations
   of schema information, the subschemaSubentry attribute is not present
   in the root DSE.  If the server masters directory entries under one
   or more schema rules, there may be any number of values of the
   subschemaSubentry attribute in the root DSE.

4.  Elements of Protocol

   The LDAP protocol is described using Abstract Syntax Notation 1
   (ASN.1) [3], and is typically transferred using a subset of ASN.1
   Basic Encoding Rules [11]. In order to support future extensions to
   this protocol, clients and servers MUST ignore elements of SEQUENCE
   encodings whose tags they do not recognize.

   Note that unlike X.500, each change to the LDAP protocol other than
   through the extension mechanisms will have a different version
   number.  A client will indicate the version it supports as part of
   the bind request, described in section 4.2.  If a client has not sent
   a bind, the server MUST assume that version 3 is supported in the
   client (since version 2 required that the client bind first).

   Clients may determine the protocol version a server supports by
   reading the supportedLDAPVersion attribute from the root DSE. Servers
   which implement version 3 or later versions MUST provide this
   attribute.  Servers which only implement version 2 may not 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 {



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                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) --

   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 MUST return the notice of disconnection
   described in section 4.4.1, with resultCode protocolError, and
   immediately close the connection. In other cases that the server
   cannot parse the request received by the client, the server MUST
   return an appropriate response to the request, with the resultCode
   set to protocolError.

   If the client receives a PDU from the server which cannot be parsed,
   the client may discard the PDU, or may abruptly close the connection.

   The ASN.1 type Controls is defined in section 4.1.12.




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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 value different from the
   values of any other requests outstanding in the LDAP session of which
   this message is a part.

   A client MUST NOT send a second request with the same message ID as
   an earlier request on the same connection if the client has not
   received the final response from the earlier request.  Otherwise the
   behavior is undefined.  Typical clients increment a counter for each
   request.

   A client MUST NOT reuse the message id of an abandonRequest or of the
   abandoned operation until it has received a response from the server
   for another request invoked subsequent to the abandonRequest, as the
   abandonRequest itself does not have a response.

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 ISO
   10646 [13] character set (a superset of Unicode) is used, encoded
   following the UTF-8 algorithm [14]. 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

   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.

        LDAPOID ::= OCTET STRING

   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 [4], such that



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         ::= 

         ::= 

   where  and  are as defined in [4].

        LDAPDN ::= LDAPString

        RelativeLDAPDN ::= LDAPString

   Only Attribute Types can be present in a relative distinguished name
   component; the options of Attribute Descriptions (next section) MUST
   NOT be used in specifying distinguished names.

4.1.4. Attribute Type

   An AttributeType takes on as its value the textual string associated
   with that AttributeType in its specification.

        AttributeType ::= LDAPString

   Each attribute type has a unique OBJECT IDENTIFIER which has been
   assigned to it.  This identifier may be written as decimal digits
   with components separated by periods, e.g. "2.5.4.10".

   A specification may also assign one or more textual names for an
   attribute type.  These names MUST begin with a letter, and only
   contain ASCII letters, digit characters and hyphens.  They are case
   insensitive.  (These ASCII characters are identical to ISO 10646
   characters whose UTF-8 encoding is a single byte between 0x00 and
   0x7F.)

   If the server has a textual name for an attribute type, it MUST use a
   textual name for attributes returned in search results.  The dotted-
   decimal OBJECT IDENTIFIER is only used if there is no textual name
   for an attribute type.

   Attribute type textual names are non-unique, as two different
   specifications (neither in standards track RFCs) may choose the same
   name.

   A server which masters or shadows entries SHOULD list all the
   attribute types it supports in the subschema entries, using the
   attributeTypes attribute.  Servers which support an open-ended set of
   attributes SHOULD include at least the attributeTypes value for the
   'objectClass' attribute. Clients MAY retrieve the attributeTypes
   value from subschema entries in order to obtain the OBJECT IDENTIFIER
   and other information associated with attribute types.



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   Some attribute type names which are used in this version of LDAP are
   described in [5].  Servers may implement additional attribute types.

4.1.5. Attribute Description

   An AttributeDescription is a superset of the definition of the
   AttributeType.  It has the same ASN.1 definition, but allows
   additional options to be specified.  They are also case insensitive.

        AttributeDescription ::= LDAPString

   A value of AttributeDescription is based on the following BNF:

         ::=  [ ";"  ]

          ::=  |  ";" 

           ::=  *

         ::=  ASCII-equivalent letters, numbers and hyphen

   Examples of valid AttributeDescription:

        cn
        userCertificate;binary

   One option, "binary", is defined in this document.  Additional
   options may be defined in IETF standards-track and experimental RFCs.
   Options beginning with "x-" are reserved for private experiments.
   Any option could be associated with any AttributeType, although not
   all combinations may be supported by a server.

   An AttributeDescription with one or more options is treated as a
   subtype of the attribute type without any options.  Options present
   in an AttributeDescription are never mutually exclusive.
   Implementations MUST generate the  list sorted in ascending
   order, and servers MUST treat any two AttributeDescription with the
   same AttributeType and options as equivalent.  A server will treat an
   AttributeDescription with any options it does not implement as an
   unrecognized attribute type.

   The data type "AttributeDescriptionList" describes a list of 0 or
   more attribute types.  (A list of zero elements has special
   significance in the Search request.)

        AttributeDescriptionList ::= SEQUENCE OF
                AttributeDescription




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4.1.5.1. Binary Option

   If the "binary" option is present in an AttributeDescription, it
   overrides any string-based encoding representation defined for that
   attribute in [5]. Instead the attribute is to be transferred as a
   binary value encoded using the Basic Encoding Rules [11].  The syntax
   of the binary value is an ASN.1 data type definition which is
   referenced by the "SYNTAX" part of the attribute type definition.

   The presence or absence of the "binary" option only affects the
   transfer of attribute values in protocol; servers store any
   particular attribute in a single format.  If a client requests that a
   server return an attribute in the binary format, but the server
   cannot generate that format, the server MUST treat this attribute
   type as an unrecognized attribute type.  Similarly, clients MUST NOT
   expect servers to return an attribute in binary format if the client
   requested that attribute by name without the binary option.

   This option is intended to be used with attributes whose syntax is a
   complex ASN.1 data type, and the structure of values of that type is
   needed by clients.  Examples of this kind of syntax are "Certificate"
   and "CertificateList".

4.1.6. Attribute Value

   A field of type AttributeValue takes on as its value either a string
   encoding of a AttributeValue data type, or an OCTET STRING containing
   an encoded binary value, depending on whether the "binary" option is
   present in the companion AttributeDescription to this AttributeValue.

   The definition of string encodings for different syntaxes and types
   may be found in other documents, and in particular [5].

        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 NEITHER simply 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 which are not
   valid according to the syntax defined for the attributes.




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4.1.7. 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

   If the "binary" option is present in attributeDesc, this signals to
   the server that the assertionValue is a binary encoding of the
   assertion value.

   For all the string-valued user attributes described in [5], the
   assertion value syntax is the same as the value syntax.  Clients may
   use attribute values as assertion values in compare requests and
   search filters.

   Note however that the assertion syntax may be different from the
   value syntax for other attributes or for non-equality matching rules.
   These may have an assertion syntax which contains only part of the
   value.  See section 20.2.1.8 of X.501 [6] for examples.

4.1.8. Attribute

   An attribute consists of a type and one or more values of that type.
   (Though attributes MUST have at least one value when stored, due to
   access control restrictions the set may be empty when transferred in
   protocol.  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
   order of attribute values within the vals set is undefined and
   implementation-dependent, and MUST NOT be relied upon.

4.1.9. Matching Rule Identifier

   A matching rule is a means of expressing how a server should compare
   an AssertionValue received in a search filter with an abstract data
   value.  The matching rule defines the syntax of the assertion value
   and the process to be performed in the server.



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   An X.501(1993) Matching Rule is identified in the LDAP protocol by
   the printable representation of its OBJECT IDENTIFIER, either as one
   of the strings given in [5], or as decimal digits with components
   separated by periods, 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
   information is given in section 4.4 of [5].

4.1.10. Result Message

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

        LDAPResult ::= SEQUENCE {
                resultCode      ENUMERATED {
                             success                      (0),
                             operationsError              (1),
                             protocolError                (2),
                             timeLimitExceeded            (3),
                             sizeLimitExceeded            (4),
                             compareFalse                 (5),
                             compareTrue                  (6),

                             authMethodNotSupported       (7),
                             strongAuthRequired           (8),
                                        -- 9 reserved --
                             referral                     (10),  -- new
                             adminLimitExceeded           (11),  -- new
                             unavailableCriticalExtension (12),  -- new
                             confidentialityRequired      (13),  -- new
                             saslBindInProgress           (14),  -- new
                             noSuchAttribute              (16),
                             undefinedAttributeType       (17),
                             inappropriateMatching        (18),
                             constraintViolation          (19),
                             attributeOrValueExists       (20),
                             invalidAttributeSyntax       (21),
                                        -- 22-31 unused --



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                             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), -- new
                                        -- 72-79 unused --
                             other                        (80) },
                             -- 81-90 reserved for APIs --
                matchedDN       LDAPDN,
                errorMessage    LDAPString,
                referral        [3] Referral OPTIONAL }

   All the result codes with the exception of success, compareFalse and
   compareTrue are to be treated as meaning the operation could not be
   completed in its entirety.

   Most of the result codes are based on problem indications from X.511
   error data types.  Result codes from 16 to 21 indicate an
   AttributeProblem, codes 32, 33, 34 and 36 indicate a NameProblem,
   codes 48, 49 and 50 indicate a SecurityProblem, codes 51 to 54
   indicate a ServiceProblem, and codes 64 to 69 and 71 indicates an
   UpdateProblem.

   If a client receives a result code which is not listed above, it is
   to be treated as an unknown error condition.

   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,




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   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.

   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 [8]. The matchedDN field is to be set to a zero length
   string with all other result codes.

4.1.11. Referral

   The referral error 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 a reference to
   another server (or set of servers) which 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.

   The referral is not returned for a singleLevel or wholeSubtree search
   in which the search scope spans multiple naming contexts, and several
   different servers would need to be contacted to complete the
   operation. Instead, continuation references, described in section
   4.5.3, are returned.

        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 any one of servers.  All the URLs MUST be
   equally capable of being used to progress the operation.  (The
   mechanisms for how this is achieved by multiple servers are outside
   the scope of this document.)

   URLs for servers implementing the LDAP protocol are written according
   to [9].  If an alias was dereferenced, the  part of the URL MUST
   be present, with the new target object name.  If the  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



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   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.

   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 RFC 1738 [7].

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

4.1.12. Controls

   A control is a way to specify extension information. Controls which
   are sent as part of a request apply only to that request and are not
   saved.

        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.

   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 and the criticality
   field is TRUE, the server MUST NOT perform the operation, and MUST
   instead return the resultCode unsupportedCriticalExtension.

   If the control is not appropriate for the operation and criticality
   field is TRUE, the server MUST NOT perform the operation, and MUST
   instead return the resultCode unsupportedCriticalExtension.

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





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   The controlValue contains any information associated with the
   control, and its format is defined for the control.  The server 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 define any controls.  Controls may be defined
   in other documents.  The definition of a control consists of:

     - the OBJECT IDENTIFIER assigned to the control,

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

     - the format of the controlValue contents of the control.

   Servers list the controls which they recognize in the
   supportedControl attribute in the root DSE.

4.2. Bind Operation

   The function of the Bind Operation is to allow authentication
   information to be exchanged between the client and server.

   The Bind 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 version it desires.
     If the client requests protocol version 2, a server that supports
     the version 2 protocol as described in [2] will not return any v3-



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     specific protocol fields.  (Note that not all LDAP servers will
     support protocol version 2, since they may be unable to generate
     the attribute syntaxes associated with version 2.)

   - 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 LDAPDN in the credentials.

   - authentication: information used to authenticate the name, if any,
     provided in the Bind Request.

   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.

   Unlike LDAP v2, the client need not send a Bind Request in the first
   PDU of the connection.  The client may request any operations and the
   server MUST treat these as unauthenticated. If the server requires
   that the client bind before browsing or modifying the directory, the
   server MAY reject a request other than binding, unbinding or an
   extended request with the "operationsError" result.




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

   Clients MAY send multiple bind requests on a connection to change
   their credentials.  A subsequent bind process has the effect of
   abandoning all operations outstanding on the connection.  (This
   simplifies server implementation.)  Authentication from earlier binds
   are subsequently ignored, and so if the bind fails, the connection
   will be treated as anonymous. If a SASL transfer encryption or
   integrity mechanism has been negotiated, and that mechanism does not
   support the changing of credentials from one identity to another,
   then the client MUST instead establish a new connection.

4.2.2. Authentication and Other Security Services

   The simple authentication option provides minimal authentication
   facilities, with the contents of the authentication field consisting
   only of a cleartext password.  Note that the use of cleartext
   passwords is not recommended over open networks when there is no
   authentication or encryption being performed by a lower layer; see
   the "Security Considerations" section.

   If no authentication is to be performed, then the simple
   authentication option MUST be chosen, and the password be of zero
   length.  (This is often done by LDAPv2 clients.)  Typically the DN is
   also of zero length.

   The sasl choice allows for any mechanism defined for use with SASL
   [12].  The mechanism field contains the name of the mechanism.  The
   credentials field contains the arbitrary data used for
   authentication, inside an OCTET STRING wrapper.  Note that unlike
   some Internet application protocols where SASL is used, LDAP is not
   text-based, thus no base64 transformations are performed on the
   credentials.

   If any SASL-based integrity or confidentiality services are enabled,
   they take effect following the transmission by the server and
   reception by the client of the final BindResponse with resultCode
   success.

   The client can request that the server use authentication information
   from a lower layer protocol by using the SASL EXTERNAL mechanism.





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4.2.3. 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 he
   status of the client's request for authentication.

   f the bind was successful, the resultCode will be success, therwise
   it will be one of:

   - 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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   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 password 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 may assume that the protocol session
   is terminated. Upon receipt of an UnbindRequest, a protocol server
   may assume that the requesting client has terminated the session and
   that all outstanding requests may be discarded, and may 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 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





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   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.

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

   The following resultCode values are to be used in this notification:

   - 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),



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                        derefAlways             (3) },
                sizeLimit       INTEGER (0 .. maxInt),
                timeLimit       INTEGER (0 .. maxInt),
                typesOnly       BOOLEAN,
                filter          Filter,
                attributes      AttributeDescriptionList }

        Filter ::= CHOICE {
                and             [0] SET OF Filter,
                or              [1] SET 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
                substrings      SEQUENCE OF CHOICE {
                        initial [0] LDAPString,
                        any     [1] LDAPString,
                        final   [2] LDAPString } }

        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;



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             derefInSearching: dereference aliases in subordinates of
             the base object in searching, but not in locating the
             base object of the search;

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

             derefAlways: dereference aliases both in searching and in
             locating the base object of the search.

   - sizelimit: A sizelimit that restricts the maximum number of entries
     to be returned as a result of the search. A value of 0 in this
     field indicates that no client-requested sizelimit restrictions are
     in effect for the search.  Servers may enforce a maximum number of
     entries to return.

   - timelimit: A timelimit that restricts the maximum time (in seconds)
     allowed for a search. A value of 0 in this field indicates that no
     client-requested timelimit 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(93) 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.






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     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 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.






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     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
     [8].

   - 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 all user
     attributes are to be returned.  (The "*" allows the client to
     request all user attributes in addition to specific 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 control 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 [5].)

   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 existence 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 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,
   ExtendedResponse or SearchResultDone data types.

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



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                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
        -- 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 returned in binary format (indicated
   by the AttributeDescription in the response having the binary option
   present).

   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 MUST NOT assume that all attributes
   can be modified, even if permitted by access control.

   LDAPMessage responses of the ExtendedResponse form are reserved for
   returning information associated with a control requested by the
   client.  These may be defined in future versions of this document.



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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, 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.

   The SearchResultReference is of the same data type as the Referral.
   URLs for servers implementing the LDAP protocol are written according
   to [9].  The  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.  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.

   The name of an unexplored subtree in a SearchResultReference need not
   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 to
   different servers, it MUST abandon each operation individually.

4.5.3.1. Example

   For example, suppose the contacted server (hosta) holds the entry
   "O=MNN,C=WW" and the entry "CN=Manager,O=MNN,C=WW".  It knows that
   either LDAP-capable servers (hostb) or (hostc) hold
   "OU=People,O=MNN,C=WW" (one is the master and the other server a




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   shadow), and that LDAP-capable server (hostd) holds the subtree
   "OU=Roles,O=MNN,C=WW".  If a subtree search of "O=MNN,C=WW" is
   requested to the contacted server, it may return the following:

     SearchResultEntry for O=MNN,C=WW
     SearchResultEntry for CN=Manager,O=MNN,C=WW
     SearchResultReference {
       ldap://hostb/OU=People,O=MNN,C=WW
       ldap://hostc/OU=People,O=MNN,C=WW
     }
     SearchResultReference {
       ldap://hostd/OU=Roles,O=MNN,C=WW
     }
     SearchResultDone (success)

   Client implementors should note that when following a
   SearchResultReference, additional SearchResultReference may be
   generated.  Continuing the example, if the client contacted the
   server (hostb) and issued the search for the subtree
   "OU=People,O=MNN,C=WW", the server might respond as follows:

     SearchResultEntry for OU=People,O=MNN,C=WW
     SearchResultReference {
      ldap://hoste/OU=Managers,OU=People,O=MNN,C=WW
     }
     SearchResultReference {
      ldap://hostf/OU=Consultants,OU=People,O=MNN,C=WW
     }
     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 "O=XYZ,C=US" 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 {



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                        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 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
             attribute does not exist.

   The result of the modify 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.





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   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 match filter has not been defined for an attribute type,
   clients MUST NOT attempt to delete individual values of that attribute
   from an entry using the "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
   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.




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   - 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 the createTimestamp or
     creatorsName attributes, since these will be generated
     automatically by the server.

   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,O=Foo,C=US", the "O=Foo,C=US" entry did not exist, and the
   "C=US" entry did exist, then the server would return the error
   noSuchObject with the matchedDN field containing "C=US".  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.  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.

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:



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        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.

   - 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.

   - 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




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   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.

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

   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. The result of the comparison will be
   returned to the client in the Compare Response. Note that errors and
   the result of comparison are all returned in the same construct.





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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.  In a search result, it may be that an
   attribute of that type would be returned, but with an empty set of
   values.

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

   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).

   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.






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   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. Mapping Onto BER-based Transport Services

   The protocol elements of LDAP are encoded for exchange using the
   Basic Encoding Rules (BER) [11] of ASN.1 [3]. 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.

   (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".






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   (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
   noted.

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 LDAPMessage PDUs are mapped directly onto the TCP bytestream.  It
   is recommended that server implementations running over the TCP MAY
   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 [5].  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.

   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.



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7.  Security Considerations

   When used with a connection-oriented transport, this version of the
   protocol provides facilities for the LDAP v2 authentication
   mechanism, simple authentication using a cleartext password, as well
   as any SASL mechanism [12].  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 cache.

8.  Acknowledgements

   This document is an update to RFC 1777, by Wengyik Yeong, Tim Howes,
   and Steve Kille.  Design ideas included in this document are based on
   those discussed in ASID and other IETF Working Groups.  The
   contributions of individuals in these working groups is gratefully
   acknowledged.

9.  Bibliography

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

   [2] Yeong, W., Howes, T., and S. Kille, "Lightweight Directory Access
       Protocol", RFC 1777, March 1995.

   [3] ITU-T Rec. X.680, "Abstract Syntax Notation One (ASN.1) -
       Specification of Basic Notation", 1994.




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   [4] Kille, S., Wahl, M., and T. Howes, "Lightweight Directory Access
       Protocol (v3): UTF-8 String Representation of Distinguished
       Names", RFC 2253, December 1997.

   [5] Wahl, M., Coulbeck, A., Howes, T., and S. Kille, "Lightweight
       Directory Access Protocol (v3): Attribute Syntax Definitions",
       RFC 2252, December 1997.

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

   [7] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
       Resource  Locators (URL)", RFC 1738, December 1994.

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

   [9] Howes, T., and M. Smith, "The LDAP URL Format", RFC 2255,
       December 1997.

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

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

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

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

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

10. Authors' Addresses

   Mark Wahl
   Critical Angle Inc.
   4815 W Braker Lane #502-385
   Austin, TX 78759
   USA

   Phone:  [phone]
   EMail:  [e-mail]






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   Tim Howes
   Netscape Communications Corp.
   501 E. Middlefield Rd., MS MV068
   Mountain View, CA 94043
   USA

   Phone:  [phone]
   EMail:   [e-mail]

   Steve Kille
   Isode Limited
   The Dome, The Square
   Richmond
   TW9 1DT
   UK

   Phone:  [phone]
   EMail:  [e-mail]

































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Appendix A - Complete ASN.1 Definition

        Lightweight-Directory-Access-Protocol-V3 DEFINITIONS
        IMPLICIT TAGS ::=

        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

        LDAPOID ::= OCTET STRING

        LDAPDN ::= LDAPString

        RelativeLDAPDN ::= LDAPString

        AttributeType ::= LDAPString

        AttributeDescription ::= LDAPString




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        AttributeDescriptionList ::= SEQUENCE OF
                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),  -- new
                             adminLimitExceeded           (11),  -- new
                             unavailableCriticalExtension (12),  -- new
                             confidentialityRequired      (13),  -- new
                             saslBindInProgress           (14),  -- new
                             noSuchAttribute              (16),
                             undefinedAttributeType       (17),
                             inappropriateMatching        (18),
                             constraintViolation          (19),
                             attributeOrValueExists       (20),
                             invalidAttributeSyntax       (21),
                                        -- 22-31 unused --
                             noSuchObject                 (32),
                             aliasProblem                 (33),
                             invalidDNSyntax              (34),
                             -- 35 reserved for undefined isLeaf --
                             aliasDereferencingProblem    (36),
                                        -- 37-47 unused --
                             inappropriateAuthentication  (48),



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                             invalidCredentials           (49),
                             insufficientAccessRights     (50),
                             busy                         (51),
                             unavailable                  (52),
                             unwillingToPerform           (53),
                             loopDetect                   (54),
                                        -- 55-63 unused --
                             namingViolation              (64),
                             objectClassViolation         (65),
                             notAllowedOnNonLeaf          (66),
                             notAllowedOnRDN              (67),
                             entryAlreadyExists           (68),
                             objectClassModsProhibited    (69),
                                        -- 70 reserved for CLDAP --
                             affectsMultipleDSAs          (71), -- new
                                        -- 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 {



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             COMPONENTS OF LDAPResult,
             serverSaslCreds    [7] OCTET STRING OPTIONAL }

        UnbindRequest ::= [APPLICATION 2] NULL

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

        Filter ::= CHOICE {
                and             [0] SET OF Filter,
                or              [1] SET 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
                substrings      SEQUENCE OF CHOICE {
                        initial [0] LDAPString,
                        any     [1] LDAPString,
                        final   [2] LDAPString } }

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




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        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 {
                        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



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        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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Full Copyright Statement

   Copyright (C) The Internet Society (1997).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
























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