GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc: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.

Wahl, et. al. Standards Track [Page 1] RFC 2251 LDAPv3 December 1997

 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

Wahl, et. al. Standards Track [Page 2] RFC 2251 LDAPv3 December 1997

 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:
  1. 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.
  1. Most protocol data elements can be encoded as ordinary strings

(e.g., Distinguished Names).

Wahl, et. al. Standards Track [Page 3] RFC 2251 LDAPv3 December 1997

  1. Referrals to other servers may be returned.
  1. SASL mechanisms may be used with LDAP to provide association

security services.

  1. Attribute values and Distinguished Names have been

internationalized through the use of the ISO 10646 character set.

  1. The protocol can be extended to support new operations, and

controls may be used to extend existing operations.

  1. 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.

Wahl, et. al. Standards Track [Page 4] RFC 2251 LDAPv3 December 1997

 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

Wahl, et. al. Standards Track [Page 5] RFC 2251 LDAPv3 December 1997

 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. "foo@bar.com" will match "FOO@BAR.COM").
 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:

Wahl, et. al. Standards Track [Page 6] RFC 2251 LDAPv3 December 1997

  1. creatorsName: the Distinguished Name of the user who added this

entry to the directory.

  1. createTimestamp: the time this entry was added to the directory.
  1. modifiersName: the Distinguished Name of the user who last modified

this entry.

  1. modifyTimestamp: the time this entry was last modified.
  1. 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:
  1. cn: this attribute MUST be used to form the RDN of the subschema

entry.

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

"subschema".

  1. objectClasses: each value of this attribute specifies an object

class known to the server.

  1. 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.

Wahl, et. al. Standards Track [Page 7] RFC 2251 LDAPv3 December 1997

 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.
  1. namingContexts: naming contexts held in the server. Naming contexts

are defined in section 17 of X.501 [6].

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

server.

  1. altServer: alternative servers in case this one is later

unavailable.

Wahl, et. al. Standards Track [Page 8] RFC 2251 LDAPv3 December 1997

  1. supportedExtension: list of supported extended operations.
  1. supportedControl: list of supported controls.
  1. supportedSASLMechanisms: list of supported SASL security features.
  1. 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 {

Wahl, et. al. Standards Track [Page 9] RFC 2251 LDAPv3 December 1997

              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.

Wahl, et. al. Standards Track [Page 10] RFC 2251 LDAPv3 December 1997

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

Wahl, et. al. Standards Track [Page 11] RFC 2251 LDAPv3 December 1997

      <distinguished-name> ::= <name>
      <relative-distinguished-name> ::= <name-component>
 where <name> and <name-component> 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.

Wahl, et. al. Standards Track [Page 12] RFC 2251 LDAPv3 December 1997

 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:
      <AttributeDescription> ::= <AttributeType> [ ";" <options> ]
      <options>  ::= <option> | <option> ";" <options>
      <option>   ::= <opt-char> <opt-char>*
      <opt-char> ::=  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 <options> 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

Wahl, et. al. Standards Track [Page 13] RFC 2251 LDAPv3 December 1997

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.

Wahl, et. al. Standards Track [Page 14] RFC 2251 LDAPv3 December 1997

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.

Wahl, et. al. Standards Track [Page 15] RFC 2251 LDAPv3 December 1997

 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 --

Wahl, et. al. Standards Track [Page 16] RFC 2251 LDAPv3 December 1997

                           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,

Wahl, et. al. Standards Track [Page 17] RFC 2251 LDAPv3 December 1997

 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 <dn> part of the URL MUST
 be present, with the new target object name.  If the <dn> part is
 present, the client MUST use this name in its next request to
 progress the operation, and if it is not present the client will use
 the same name as in the original request.  Some servers (e.g.
 participating in distributed indexing) may provide a different filter
 in a referral for a search operation.  If the filter part of the URL

Wahl, et. al. Standards Track [Page 18] RFC 2251 LDAPv3 December 1997

 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.

Wahl, et. al. Standards Track [Page 19] RFC 2251 LDAPv3 December 1997

 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:
  1. the OBJECT IDENTIFIER assigned to the control,
  1. whether the control is always noncritical, always critical, or

critical at the client's option,

  1. 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:
  1. 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-

Wahl, et. al. Standards Track [Page 20] RFC 2251 LDAPv3 December 1997

   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.)
  1. 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.
  1. 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.

Wahl, et. al. Standards Track [Page 21] RFC 2251 LDAPv3 December 1997

 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.

Wahl, et. al. Standards Track [Page 22] RFC 2251 LDAPv3 December 1997

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:
  1. operationsError: server encountered an internal error,
  1. protocolError: unrecognized version number or incorrect PDU

structure,

  1. authMethodNotSupported: unrecognized SASL mechanism name,
  1. strongAuthRequired: the server requires authentication be

performed with a SASL mechanism,

  1. referral: this server cannot accept this bind and the client

should try another,

  1. saslBindInProgress: the server requires the client to send a

new bind request, with the same sasl mechanism, to continue the

   authentication process,
  1. inappropriateAuthentication: the server requires the client

which had attempted to bind anonymously or without supplying

   credentials to provide some form of credentials,
  1. invalidCredentials: the wrong password was supplied or the SASL

credentials could not be processed,

  1. 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.)

Wahl, et. al. Standards Track [Page 23] RFC 2251 LDAPv3 December 1997

 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

Wahl, et. al. Standards Track [Page 24] RFC 2251 LDAPv3 December 1997

 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:
  1. protocolError: The server has received data from the client in

which

   the LDAPMessage structure could not be parsed.
  1. strongAuthRequired: The server has detected that an established

underlying security association protecting communication between

   the client and server has unexpectedly failed or been compromised.
  1. 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),

Wahl, et. al. Standards Track [Page 25] RFC 2251 LDAPv3 December 1997

                      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:
  1. baseObject: An LDAPDN that is the base object entry relative to

which the search is to be performed.

  1. 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.
  1. 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;

Wahl, et. al. Standards Track [Page 26] RFC 2251 LDAPv3 December 1997

           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.
  1. 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.
  1. 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.
  1. 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.
  1. 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.

Wahl, et. al. Standards Track [Page 27] RFC 2251 LDAPv3 December 1997

   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.

Wahl, et. al. Standards Track [Page 28] RFC 2251 LDAPv3 December 1997

   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].
  1. 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,

Wahl, et. al. Standards Track [Page 29] RFC 2251 LDAPv3 December 1997

              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.

Wahl, et. al. Standards Track [Page 30] RFC 2251 LDAPv3 December 1997

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 <dn> part MUST be present in the URL, with the new target
 object name.  The client MUST use this name in its next request.
 Some servers (e.g. part of a distributed index exchange system) may
 provide a different filter in the URLs of the SearchResultReference.
 If the filter part of the URL is present in an LDAP URL, the client
 MUST use the new filter in its next request to progress the search,
 and if the filter part is absent the client will use again the same
 filter.  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

Wahl, et. al. Standards Track [Page 31] RFC 2251 LDAPv3 December 1997

 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 {

Wahl, et. al. Standards Track [Page 32] RFC 2251 LDAPv3 December 1997

                      operation       ENUMERATED {
                                              add     (0),
                                              delete  (1),
                                              replace (2) },
                      modification    AttributeTypeAndValues } }
      AttributeTypeAndValues ::= SEQUENCE {
              type    AttributeDescription,
              vals    SET OF AttributeValue }
 Parameters of the Modify Request are:
  1. 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.
  1. 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.

Wahl, et. al. Standards Track [Page 33] RFC 2251 LDAPv3 December 1997

 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:
  1. 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.

Wahl, et. al. Standards Track [Page 34] RFC 2251 LDAPv3 December 1997

  1. 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:

Wahl, et. al. Standards Track [Page 35] RFC 2251 LDAPv3 December 1997

      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:
  1. entry: the Distinguished Name of the entry to be changed. This

entry may or may not have subordinate entries.

  1. newrdn: the RDN that will form the leftmost component of the new

name of the entry.

  1. 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.
  1. 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

Wahl, et. al. Standards Track [Page 36] RFC 2251 LDAPv3 December 1997

 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:
  1. entry: the name of the entry to be compared with.
  1. 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.

Wahl, et. al. Standards Track [Page 37] RFC 2251 LDAPv3 December 1997

 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.

Wahl, et. al. Standards Track [Page 38] RFC 2251 LDAPv3 December 1997

 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".

Wahl, et. al. Standards Track [Page 39] RFC 2251 LDAPv3 December 1997

 (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.

Wahl, et. al. Standards Track [Page 40] RFC 2251 LDAPv3 December 1997

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.

Wahl, et. al. Standards Track [Page 41] RFC 2251 LDAPv3 December 1997

 [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:  +1 512 372-3160
 EMail:  M.Wahl@critical-angle.com

Wahl, et. al. Standards Track [Page 42] RFC 2251 LDAPv3 December 1997

 Tim Howes
 Netscape Communications Corp.
 501 E. Middlefield Rd., MS MV068
 Mountain View, CA 94043
 USA
 Phone:  +1 650 937-3419
 EMail:   howes@netscape.com
 Steve Kille
 Isode Limited
 The Dome, The Square
 Richmond
 TW9 1DT
 UK
 Phone:  +44-181-332-9091
 EMail:  S.Kille@isode.com

Wahl, et. al. Standards Track [Page 43] RFC 2251 LDAPv3 December 1997

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

Wahl, et. al. Standards Track [Page 44] RFC 2251 LDAPv3 December 1997

      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),

Wahl, et. al. Standards Track [Page 45] RFC 2251 LDAPv3 December 1997

                           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 {

Wahl, et. al. Standards Track [Page 46] RFC 2251 LDAPv3 December 1997

           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 }

Wahl, et. al. Standards Track [Page 47] RFC 2251 LDAPv3 December 1997

      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

Wahl, et. al. Standards Track [Page 48] RFC 2251 LDAPv3 December 1997

      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

Wahl, et. al. Standards Track [Page 49] RFC 2251 LDAPv3 December 1997

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.

Wahl, et. al. Standards Track [Page 50]

/data/webs/external/dokuwiki/data/pages/rfc/rfc2251.txt · Last modified: 1997/12/22 18:29 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki