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rfc:rfc4511

Network Working Group J. Sermersheim, Ed. Request for Comments: 4511 Novell, Inc. Obsoletes: 2251, 2830, 3771 June 2006 Category: Standards Track

    Lightweight Directory Access Protocol (LDAP): The Protocol

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 (2006).

Abstract

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

Table of Contents

 1. Introduction ....................................................3
    1.1. Relationship to Other LDAP Specifications ..................3
 2. Conventions .....................................................3
 3. Protocol Model ..................................................4
    3.1. Operation and LDAP Message Layer Relationship ..............5
 4. Elements of Protocol ............................................5
    4.1. Common Elements ............................................5
         4.1.1. Message Envelope ....................................6
         4.1.2. String Types ........................................7
         4.1.3. Distinguished Name and Relative Distinguished Name ..8
         4.1.4. Attribute Descriptions ..............................8
         4.1.5. Attribute Value .....................................8
         4.1.6. Attribute Value Assertion ...........................9
         4.1.7. Attribute and PartialAttribute ......................9
         4.1.8. Matching Rule Identifier ...........................10
         4.1.9. Result Message .....................................10
         4.1.10. Referral ..........................................12

Sermersheim Standards Track [Page 1] RFC 4511 LDAPv3 June 2006

         4.1.11. Controls ..........................................14
    4.2. Bind Operation ............................................16
         4.2.1. Processing of the Bind Request .....................17
         4.2.2. Bind Response ......................................18
    4.3. Unbind Operation ..........................................18
    4.4. Unsolicited Notification ..................................19
         4.4.1. Notice of Disconnection ............................19
    4.5. Search Operation ..........................................20
         4.5.1. Search Request .....................................20
         4.5.2. Search Result ......................................27
         4.5.3. Continuation References in the Search Result .......28
    4.6. Modify Operation ..........................................31
    4.7. Add Operation .............................................33
    4.8. Delete Operation ..........................................34
    4.9. Modify DN Operation .......................................34
    4.10. Compare Operation ........................................36
    4.11. Abandon Operation ........................................36
    4.12. Extended Operation .......................................37
    4.13. IntermediateResponse Message .............................39
         4.13.1. Usage with LDAP ExtendedRequest and
                 ExtendedResponse ..................................40
         4.13.2. Usage with LDAP Request Controls ..................40
    4.14. StartTLS Operation .......................................40
         4.14.1. StartTLS Request ..................................40
         4.14.2. StartTLS Response .................................41
         4.14.3. Removal of the TLS Layer ..........................41
 5. Protocol Encoding, Connection, and Transfer ....................42
    5.1. Protocol Encoding .........................................42
    5.2. Transmission Control Protocol (TCP) .......................43
    5.3. Termination of the LDAP session ...........................43
 6. Security Considerations ........................................43
 7. Acknowledgements ...............................................45
 8. Normative References ...........................................46
 9. Informative References .........................................48
 10. IANA Considerations ...........................................48
 Appendix A. LDAP Result Codes .....................................49
    A.1. Non-Error Result Codes ....................................49
    A.2. Result Codes ..............................................49
 Appendix B. Complete ASN.1 Definition .............................54
 Appendix C. Changes ...............................................60
    C.1. Changes Made to RFC 2251 ..................................60
    C.2. Changes Made to RFC 2830 ..................................66
    C.3. Changes Made to RFC 3771 ..................................66

Sermersheim Standards Track [Page 2] RFC 4511 LDAPv3 June 2006

1. Introduction

 The Directory is "a collection of open systems cooperating to provide
 directory services" [X.500].  A directory user, which may be a human
 or other entity, accesses the Directory through a client (or
 Directory User Agent (DUA)).  The client, on behalf of the directory
 user, interacts with one or more servers (or Directory System Agents
 (DSA)).  Clients interact with servers using a directory access
 protocol.
 This document details the protocol elements of the Lightweight
 Directory Access Protocol (LDAP), along with their semantics.
 Following the description of protocol elements, it describes the way
 in which the protocol elements are encoded and transferred.

1.1. Relationship to Other LDAP Specifications

 This document is an integral part of the LDAP Technical Specification
 [RFC4510], which obsoletes the previously defined LDAP technical
 specification, RFC 3377, in its entirety.
 This document, together with [RFC4510], [RFC4513], and [RFC4512],
 obsoletes RFC 2251 in its entirety.  Section 3.3 is obsoleted by
 [RFC4510].  Sections 4.2.1 (portions) and 4.2.2 are obsoleted by
 [RFC4513].  Sections 3.2, 3.4, 4.1.3 (last paragraph), 4.1.4, 4.1.5,
 4.1.5.1, 4.1.9 (last paragraph), 5.1, 6.1, and 6.2 (last paragraph)
 are obsoleted by [RFC4512].  The remainder of RFC 2251 is obsoleted
 by this document.  Appendix C.1 summarizes substantive changes in the
 remainder.
 This document obsoletes RFC 2830, Sections 2 and 4.  The remainder of
 RFC 2830 is obsoleted by [RFC4513].  Appendix C.2 summarizes
 substantive changes to the remaining sections.
 This document also obsoletes RFC 3771 in entirety.

2. Conventions

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", and "MAY" in this document are
 to be interpreted as described in [RFC2119].
 Character names in this document use the notation for code points and
 names from the Unicode Standard [Unicode].  For example, the letter
 "a" may be represented as either <U+0061> or <LATIN SMALL LETTER A>.

Sermersheim Standards Track [Page 3] RFC 4511 LDAPv3 June 2006

 Note: a glossary of terms used in Unicode can be found in [Glossary].
 Information on the Unicode character encoding model can be found in
 [CharModel].
 The term "transport connection" refers to the underlying transport
 services used to carry the protocol exchange, as well as associations
 established by these services.
 The term "TLS layer" refers to Transport Layer Security (TLS)
 services used in providing security services, as well as associations
 established by these services.
 The term "SASL layer" refers to Simply Authentication and Security
 Layer (SASL) services used in providing security services, as well as
 associations established by these services.
 The term "LDAP message layer" refers to the LDAP Message Protocol
 Data Unit (PDU) services used in providing directory services, as
 well as associations established by these services.
 The term "LDAP session" refers to combined services (transport
 connection, TLS layer, SASL layer, LDAP message layer) and their
 associations.
 See the table in Section 5 for an illustration of these four terms.

3. Protocol Model

 The general model adopted by this protocol is one of clients
 performing protocol operations against servers.  In this model, a
 client transmits a protocol request describing the operation to be
 performed to a server.  The server is then responsible for performing
 the necessary operation(s) in the Directory.  Upon completion of an
 operation, the server typically returns a response containing
 appropriate data to the requesting client.
 Protocol operations are generally independent of one another.  Each
 operation is processed as an atomic action, leaving the directory in
 a consistent state.
 Although servers are required to return responses whenever such
 responses are defined in the protocol, there is no requirement for
 synchronous behavior on the part of either clients or servers.
 Requests and responses for multiple operations generally may be
 exchanged between a client and server in any order.  If required,
 synchronous behavior may be controlled by client applications.

Sermersheim Standards Track [Page 4] RFC 4511 LDAPv3 June 2006

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

3.1. Operation and LDAP Message Layer Relationship

 Protocol operations are exchanged at the LDAP message layer.  When
 the transport connection is closed, any uncompleted operations at the
 LDAP message layer are abandoned (when possible) or are completed
 without transmission of the response (when abandoning them is not
 possible).  Also, when the transport connection is closed, the client
 MUST NOT assume that any uncompleted update operations have succeeded
 or failed.

4. Elements of Protocol

 The protocol is described using Abstract Syntax Notation One
 ([ASN.1]) and is transferred using a subset of ASN.1 Basic Encoding
 Rules ([BER]).  Section 5 specifies how the protocol elements are
 encoded and transferred.
 In order to support future extensions to this protocol, extensibility
 is implied where it is allowed per ASN.1 (i.e., sequence, set,
 choice, and enumerated types are extensible).  In addition, ellipses
 (...) have been supplied in ASN.1 types that are explicitly
 extensible as discussed in [RFC4520].  Because of the implied
 extensibility, clients and servers MUST (unless otherwise specified)
 ignore trailing SEQUENCE components whose tags they do not recognize.
 Changes to the protocol other than through the extension mechanisms
 described here require a different version number.  A client
 indicates the version it is using as part of the BindRequest,
 described in Section 4.2.  If a client has not sent a Bind, the
 server MUST assume the client is using version 3 or later.
 Clients may attempt to determine the protocol versions a server
 supports by reading the 'supportedLDAPVersion' attribute from the
 root DSE (DSA-Specific Entry) [RFC4512].

4.1. Common Elements

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

Sermersheim Standards Track [Page 5] RFC 4511 LDAPv3 June 2006

4.1.1. Message Envelope

 For the purposes of protocol exchanges, all protocol operations are
 encapsulated in a common envelope, the LDAPMessage, which is defined
 as follows:
      LDAPMessage ::= SEQUENCE {
           messageID       MessageID,
           protocolOp      CHOICE {
                bindRequest           BindRequest,
                bindResponse          BindResponse,
                unbindRequest         UnbindRequest,
                searchRequest         SearchRequest,
                searchResEntry        SearchResultEntry,
                searchResDone         SearchResultDone,
                searchResRef          SearchResultReference,
                modifyRequest         ModifyRequest,
                modifyResponse        ModifyResponse,
                addRequest            AddRequest,
                addResponse           AddResponse,
                delRequest            DelRequest,
                delResponse           DelResponse,
                modDNRequest          ModifyDNRequest,
                modDNResponse         ModifyDNResponse,
                compareRequest        CompareRequest,
                compareResponse       CompareResponse,
                abandonRequest        AbandonRequest,
                extendedReq           ExtendedRequest,
                extendedResp          ExtendedResponse,
                ...,
                intermediateResponse  IntermediateResponse },
           controls       [0] Controls OPTIONAL }
      MessageID ::= INTEGER (0 ..  maxInt)
      maxInt INTEGER ::= 2147483647 -- (2^^31 - 1) --
 The ASN.1 type Controls is defined in Section 4.1.11.
 The function of the LDAPMessage is to provide an envelope containing
 common fields required in all protocol exchanges.  At this time, the
 only common fields are the messageID and the controls.
 If the server receives an LDAPMessage from the client in which the
 LDAPMessage SEQUENCE tag cannot be recognized, the messageID cannot
 be parsed, the tag of the protocolOp is not recognized as a request,
 or the encoding structures or lengths of data fields are found to be
 incorrect, then the server SHOULD return the Notice of Disconnection

Sermersheim Standards Track [Page 6] RFC 4511 LDAPv3 June 2006

 described in Section 4.4.1, with the resultCode set to protocolError,
 and MUST immediately terminate the LDAP session as described in
 Section 5.3.
 In other cases where the client or server cannot parse an LDAP PDU,
 it SHOULD abruptly terminate the LDAP session (Section 5.3) where
 further communication (including providing notice) would be
 pernicious.  Otherwise, server implementations MUST return an
 appropriate response to the request, with the resultCode set to
 protocolError.

4.1.1.1. MessageID

 All LDAPMessage envelopes encapsulating responses contain the
 messageID value of the corresponding request LDAPMessage.
 The messageID of a request MUST have a non-zero value different from
 the messageID of any other request in progress in the same LDAP
 session.  The zero value is reserved for the unsolicited notification
 message.
 Typical clients increment a counter for each request.
 A client MUST NOT send a request with the same messageID as an
 earlier request in the same LDAP session unless it can be determined
 that the server is no longer servicing the earlier request (e.g.,
 after the final response is received, or a subsequent Bind
 completes).  Otherwise, the behavior is undefined.  For this purpose,
 note that Abandon and successfully abandoned operations do not send
 responses.

4.1.2. String Types

 The LDAPString is a notational convenience to indicate that, although
 strings of LDAPString type encode as ASN.1 OCTET STRING types, the
 [ISO10646] character set (a superset of [Unicode]) is used, encoded
 following the UTF-8 [RFC3629] algorithm.  Note that Unicode
 characters U+0000 through U+007F are the same as ASCII 0 through 127,
 respectively, and have the same single octet UTF-8 encoding.  Other
 Unicode characters have a multiple octet UTF-8 encoding.
      LDAPString ::= OCTET STRING -- UTF-8 encoded,
                                  -- [ISO10646] characters
 The LDAPOID is a notational convenience to indicate that the
 permitted value of this string is a (UTF-8 encoded) dotted-decimal
 representation of an OBJECT IDENTIFIER.  Although an LDAPOID is

Sermersheim Standards Track [Page 7] RFC 4511 LDAPv3 June 2006

 encoded as an OCTET STRING, values are limited to the definition of
 <numericoid> given in Section 1.4 of [RFC4512].
      LDAPOID ::= OCTET STRING -- Constrained to <numericoid>
                               -- [RFC4512]
 For example,
      1.3.6.1.4.1.1466.1.2.3

4.1.3. Distinguished Name and Relative Distinguished Name

 An LDAPDN is defined to be the representation of a Distinguished Name
 (DN) after encoding according to the specification in [RFC4514].
      LDAPDN ::= LDAPString
                 -- Constrained to <distinguishedName> [RFC4514]
 A RelativeLDAPDN is defined to be the representation of a Relative
 Distinguished Name (RDN) after encoding according to the
 specification in [RFC4514].
      RelativeLDAPDN ::= LDAPString
                         -- Constrained to <name-component> [RFC4514]

4.1.4. Attribute Descriptions

 The definition and encoding rules for attribute descriptions are
 defined in Section 2.5 of [RFC4512].  Briefly, an attribute
 description is an attribute type and zero or more options.
      AttributeDescription ::= LDAPString
                              -- Constrained to <attributedescription>
                              -- [RFC4512]

4.1.5. Attribute Value

 A field of type AttributeValue is an OCTET STRING containing an
 encoded attribute value.  The attribute value is encoded according to
 the LDAP-specific encoding definition of its corresponding syntax.
 The LDAP-specific encoding definitions for different syntaxes and
 attribute types may be found in other documents and in particular
 [RFC4517].
      AttributeValue ::= OCTET STRING

Sermersheim Standards Track [Page 8] RFC 4511 LDAPv3 June 2006

 Note that there is no defined limit on the size of this encoding;
 thus, protocol values may include multi-megabyte attribute values
 (e.g., photographs).
 Attribute values may be defined that have arbitrary and non-printable
 syntax.  Implementations MUST NOT display or attempt to decode an
 attribute value if its syntax is not known.  The implementation may
 attempt to discover the subschema of the source entry and to retrieve
 the descriptions of 'attributeTypes' from it [RFC4512].
 Clients MUST only send attribute values in a request that are valid
 according to the syntax defined for the attributes.

4.1.6. Attribute Value Assertion

 The AttributeValueAssertion (AVA) type definition is similar to the
 one in the X.500 Directory standards.  It contains an attribute
 description and a matching rule ([RFC4512], Section 4.1.3) assertion
 value suitable for that type.  Elements of this type are typically
 used to assert that the value in assertionValue matches a value of an
 attribute.
      AttributeValueAssertion ::= SEQUENCE {
           attributeDesc   AttributeDescription,
           assertionValue  AssertionValue }
      AssertionValue ::= OCTET STRING
 The syntax of the AssertionValue depends on the context of the LDAP
 operation being performed.  For example, the syntax of the EQUALITY
 matching rule for an attribute is used when performing a Compare
 operation.  Often this is the same syntax used for values of the
 attribute type, but in some cases the assertion syntax differs from
 the value syntax.  See objectIdentiferFirstComponentMatch in
 [RFC4517] for an example.

4.1.7. Attribute and PartialAttribute

 Attributes and partial attributes consist of an attribute description
 and attribute values.  A PartialAttribute allows zero values, while
 Attribute requires at least one value.
      PartialAttribute ::= SEQUENCE {
           type       AttributeDescription,
           vals       SET OF value AttributeValue }

Sermersheim Standards Track [Page 9] RFC 4511 LDAPv3 June 2006

      Attribute ::= PartialAttribute(WITH COMPONENTS {
           ...,
           vals (SIZE(1..MAX))})
 No two of the attribute values may be equivalent as described by
 Section 2.2 of [RFC4512].  The set of attribute values is unordered.
 Implementations MUST NOT rely upon the ordering being repeatable.

4.1.8. Matching Rule Identifier

 Matching rules are defined in Section 4.1.3 of [RFC4512].  A matching
 rule is identified in the protocol by the printable representation of
 either its <numericoid> or one of its short name descriptors
 [RFC4512], e.g., 'caseIgnoreMatch' or '2.5.13.2'.
      MatchingRuleId ::= LDAPString

4.1.9. Result Message

 The LDAPResult is the construct used in this protocol to return
 success or failure indications from servers to clients.  To various
 requests, servers will return responses containing the elements found
 in LDAPResult to indicate the final status of the protocol operation
 request.
      LDAPResult ::= SEQUENCE {
           resultCode         ENUMERATED {
                success                      (0),
                operationsError              (1),
                protocolError                (2),
                timeLimitExceeded            (3),
                sizeLimitExceeded            (4),
                compareFalse                 (5),
                compareTrue                  (6),
                authMethodNotSupported       (7),
                strongerAuthRequired         (8),
                     -- 9 reserved --
                referral                     (10),
                adminLimitExceeded           (11),
                unavailableCriticalExtension (12),
                confidentialityRequired      (13),
                saslBindInProgress           (14),
                noSuchAttribute              (16),
                undefinedAttributeType       (17),
                inappropriateMatching        (18),
                constraintViolation          (19),
                attributeOrValueExists       (20),
                invalidAttributeSyntax       (21),

Sermersheim Standards Track [Page 10] RFC 4511 LDAPv3 June 2006

  1. - 22-31 unused –

noSuchObject (32),

                aliasProblem                 (33),
                invalidDNSyntax              (34),
                     -- 35 reserved for undefined isLeaf --
                aliasDereferencingProblem    (36),
                     -- 37-47 unused --
                inappropriateAuthentication  (48),
                invalidCredentials           (49),
                insufficientAccessRights     (50),
                busy                         (51),
                unavailable                  (52),
                unwillingToPerform           (53),
                loopDetect                   (54),
                     -- 55-63 unused --
                namingViolation              (64),
                objectClassViolation         (65),
                notAllowedOnNonLeaf          (66),
                notAllowedOnRDN              (67),
                entryAlreadyExists           (68),
                objectClassModsProhibited    (69),
                     -- 70 reserved for CLDAP --
                affectsMultipleDSAs          (71),
                     -- 72-79 unused --
                other                        (80),
                ...  },
           matchedDN          LDAPDN,
           diagnosticMessage  LDAPString,
           referral           [3] Referral OPTIONAL }
 The resultCode enumeration is extensible as defined in Section 3.8 of
 [RFC4520].  The meanings of the listed result codes are given in
 Appendix A.  If a server detects multiple errors for an operation,
 only one result code is returned.  The server should return the
 result code that best indicates the nature of the error encountered.
 Servers may return substituted result codes to prevent unauthorized
 disclosures.
 The diagnosticMessage field of this construct may, at the server's
 option, be used to return a string containing a textual, human-
 readable diagnostic message (terminal control and page formatting
 characters should be avoided).  As this diagnostic message is not
 standardized, implementations MUST NOT rely on the values returned.
 Diagnostic messages typically supplement the resultCode with
 additional information.  If the server chooses not to return a
 textual diagnostic, the diagnosticMessage field MUST be empty.

Sermersheim Standards Track [Page 11] RFC 4511 LDAPv3 June 2006

 For certain result codes (typically, but not restricted to
 noSuchObject, aliasProblem, invalidDNSyntax, and
 aliasDereferencingProblem), the matchedDN field is set (subject to
 access controls) to the name of the last entry (object or alias) used
 in finding the target (or base) object.  This will be a truncated
 form of the provided name or, if an alias was dereferenced while
 attempting to locate the entry, of the resulting name.  Otherwise,
 the matchedDN field is empty.

4.1.10. Referral

 The referral result code indicates that the contacted server cannot
 or will not perform the operation and that one or more other servers
 may be able to.  Reasons for this include:
  1. The target entry of the request is not held locally, but the server

has knowledge of its possible existence elsewhere.

  1. The operation is restricted on this server – perhaps due to a

read-only copy of an entry to be modified.

 The referral field is present in an LDAPResult if the resultCode is
 set to referral, and it is absent with all other result codes.  It
 contains one or more references to one or more servers or services
 that may be accessed via LDAP or other protocols.  Referrals can be
 returned in response to any operation request (except Unbind and
 Abandon, which do not have responses).  At least one URI MUST be
 present in the Referral.
 During a Search operation, after the baseObject is located, and
 entries are being evaluated, the referral is not returned.  Instead,
 continuation references, described in Section 4.5.3, are returned
 when other servers would need to be contacted to complete the
 operation.
      Referral ::= SEQUENCE SIZE (1..MAX) OF uri URI
      URI ::= LDAPString     -- limited to characters permitted in
                             -- URIs
 If the client wishes to progress the operation, it contacts one of
 the supported services found in the referral.  If multiple URIs are
 present, the client assumes that any supported URI may be used to
 progress the operation.
 Clients that follow referrals MUST ensure that they do not loop
 between servers.  They MUST NOT repeatedly contact the same server
 for the same request with the same parameters.  Some clients use a

Sermersheim Standards Track [Page 12] RFC 4511 LDAPv3 June 2006

 counter that is incremented each time referral handling occurs for an
 operation, and these kinds of clients MUST be able to handle at least
 ten nested referrals while progressing the operation.
 A URI for a server implementing LDAP and accessible via TCP/IP (v4 or
 v6) [RFC793][RFC791] is written as an LDAP URL according to
 [RFC4516].
 Referral values that are LDAP URLs follow these rules:
  1. If an alias was dereferenced, the <dn> part of the LDAP URL MUST be

present, with the new target object name.

  1. It is RECOMMENDED that the <dn> part be present to avoid ambiguity.
  1. If the <dn> part is present, the client uses this name in its next

request to progress the operation, and if it is not present the

   client uses the same name as in the original request.
  1. Some servers (e.g., participating in distributed indexing) may

provide a different filter in a URL of a referral for a Search

   operation.
  1. If the <filter> part of the LDAP URL is present, the client uses

this filter in its next request to progress this Search, and if it

   is not present the client uses the same filter as it used for that
   Search.
  1. For Search, it is RECOMMENDED that the <scope> part be present to

avoid ambiguity.

  1. If the <scope> part is missing, the scope of the original Search is

used by the client to progress the operation.

  1. Other aspects of the new request may be the same as or different

from the request that generated the referral.

 Other kinds of URIs may be returned.  The syntax and semantics of
 such URIs is left to future specifications.  Clients may ignore URIs
 that they do not support.
 UTF-8 encoded characters appearing in the string representation of a
 DN, search filter, or other fields of the referral value may not be
 legal for URIs (e.g., spaces) and MUST be escaped using the % method
 in [RFC3986].

Sermersheim Standards Track [Page 13] RFC 4511 LDAPv3 June 2006

4.1.11. Controls

 Controls provide a mechanism whereby the semantics and arguments of
 existing LDAP operations may be extended.  One or more controls may
 be attached to a single LDAP message.  A control only affects the
 semantics of the message it is attached to.
 Controls sent by clients are termed 'request controls', and those
 sent by servers are termed 'response controls'.
      Controls ::= SEQUENCE OF control Control
      Control ::= SEQUENCE {
           controlType             LDAPOID,
           criticality             BOOLEAN DEFAULT FALSE,
           controlValue            OCTET STRING OPTIONAL }
 The controlType field is the dotted-decimal representation of an
 OBJECT IDENTIFIER that uniquely identifies the control.  This
 provides unambiguous naming of controls.  Often, response control(s)
 solicited by a request control share controlType values with the
 request control.
 The criticality field only has meaning in controls attached to
 request messages (except UnbindRequest).  For controls attached to
 response messages and the UnbindRequest, the criticality field SHOULD
 be FALSE, and MUST be ignored by the receiving protocol peer.  A
 value of TRUE indicates that it is unacceptable to perform the
 operation without applying the semantics of the control.
 Specifically, the criticality field is applied as follows:
  1. If the server does not recognize the control type, determines that

it is not appropriate for the operation, or is otherwise unwilling

   to perform the operation with the control, and if the criticality
   field is TRUE, the server MUST NOT perform the operation, and for
   operations that have a response message, it MUST return with the
   resultCode set to unavailableCriticalExtension.
  1. If the server does not recognize the control type, determines that

it is not appropriate for the operation, or is otherwise unwilling

   to perform the operation with the control, and if the criticality
   field is FALSE, the server MUST ignore the control.
  1. Regardless of criticality, if a control is applied to an

operation, it is applied consistently and impartially to the

   entire operation.

Sermersheim Standards Track [Page 14] RFC 4511 LDAPv3 June 2006

 The controlValue may contain information associated with the
 controlType.  Its format is defined by the specification of the
 control.  Implementations MUST be prepared to handle arbitrary
 contents of the controlValue octet string, including zero bytes.  It
 is absent only if there is no value information that is associated
 with a control of its type.  When a controlValue is defined in terms
 of ASN.1, and BER-encoded according to Section 5.1, it also follows
 the extensibility rules in Section 4.
 Servers list the controlType of request controls they recognize in
 the 'supportedControl' attribute in the root DSE (Section 5.1 of
 [RFC4512]).
 Controls SHOULD NOT be combined unless the semantics of the
 combination has been specified.  The semantics of control
 combinations, if specified, are generally found in the control
 specification most recently published.  When a combination of
 controls is encountered whose semantics are invalid, not specified
 (or not known), the message is considered not well-formed; thus, the
 operation fails with protocolError.  Controls with a criticality of
 FALSE may be ignored in order to arrive at a valid combination.
 Additionally, unless order-dependent semantics are given in a
 specification, the order of a combination of controls in the SEQUENCE
 is ignored.  Where the order is to be ignored but cannot be ignored
 by the server, the message is considered not well-formed, and the
 operation fails with protocolError.  Again, controls with a
 criticality of FALSE may be ignored in order to arrive at a valid
 combination.
 This document does not specify any controls.  Controls may be
 specified in other documents.  Documents detailing control extensions
 are to provide for each control:
  1. the OBJECT IDENTIFIER assigned to the control,
  1. direction as to what value the sender should provide for the

criticality field (note: the semantics of the criticality field are

   defined above should not be altered by the control's
   specification),
  1. whether the controlValue field is present, and if so, the format of

its contents,

  1. the semantics of the control, and
  1. optionally, semantics regarding the combination of the control with

other controls.

Sermersheim Standards Track [Page 15] RFC 4511 LDAPv3 June 2006

4.2. Bind Operation

 The function of the Bind operation is to allow authentication
 information to be exchanged between the client and server.  The Bind
 operation should be thought of as the "authenticate" operation.
 Operational, authentication, and security-related semantics of this
 operation are given in [RFC4513].
 The Bind request is defined as follows:
      BindRequest ::= [APPLICATION 0] SEQUENCE {
           version                 INTEGER (1 ..  127),
           name                    LDAPDN,
           authentication          AuthenticationChoice }
      AuthenticationChoice ::= CHOICE {
           simple                  [0] OCTET STRING,
                                   -- 1 and 2 reserved
           sasl                    [3] SaslCredentials,
           ...  }
      SaslCredentials ::= SEQUENCE {
           mechanism               LDAPString,
           credentials             OCTET STRING OPTIONAL }
 Fields of the BindRequest are:
  1. version: A version number indicating the version of the protocol to

be used at the LDAP message layer. This document describes version

   3 of the protocol.  There is no version negotiation.  The client
   sets this field to the version it desires.  If the server does not
   support the specified version, it MUST respond with a BindResponse
   where the resultCode is set to protocolError.
  1. name: If not empty, 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 ([RFC4513],
   Section 5.1) or when using SASL [RFC4422] authentication
   ([RFC4513], Section 5.2).  Where the server attempts to locate the
   named object, it SHALL NOT perform alias dereferencing.
  1. authentication: Information used in authentication. This type is

extensible as defined in Section 3.7 of [RFC4520]. Servers that do

   not support a choice supplied by a client return a BindResponse
   with the resultCode set to authMethodNotSupported.

Sermersheim Standards Track [Page 16] RFC 4511 LDAPv3 June 2006

   Textual passwords (consisting of a character sequence with a known
   character set and encoding) transferred to the server using the
   simple AuthenticationChoice SHALL be transferred as UTF-8 [RFC3629]
   encoded [Unicode].  Prior to transfer, clients SHOULD prepare text
   passwords as "query" strings by applying the SASLprep [RFC4013]
   profile of the stringprep [RFC3454] algorithm.  Passwords
   consisting of other data (such as random octets) MUST NOT be
   altered.  The determination of whether a password is textual is a
   local client matter.

4.2.1. Processing of the Bind Request

 Before processing a BindRequest, all uncompleted operations MUST
 either complete or be abandoned.  The server may either wait for the
 uncompleted operations to complete, or abandon them.  The server then
 proceeds to authenticate the client in either a single-step or
 multi-step Bind process.  Each step requires the server to return a
 BindResponse to indicate the status of authentication.
 After sending a BindRequest, clients MUST NOT send further LDAP PDUs
 until receiving the BindResponse.  Similarly, servers SHOULD NOT
 process or respond to requests received while processing a
 BindRequest.
 If the client did not bind before sending a request and receives an
 operationsError to that request, it may then send a BindRequest.  If
 this also fails or the client chooses not to bind on the existing
 LDAP session, it may terminate the LDAP session, re-establish it, and
 begin again by first sending a BindRequest.  This will aid in
 interoperating with servers implementing other versions of LDAP.
 Clients may send multiple Bind requests to change the authentication
 and/or security associations or to complete a multi-stage Bind
 process.  Authentication from earlier binds is subsequently ignored.
 For some SASL authentication mechanisms, it may be necessary for the
 client to invoke the BindRequest multiple times ([RFC4513], Section
 5.2).  Clients MUST NOT invoke operations between two Bind requests
 made as part of a multi-stage Bind.
 A client may abort a SASL bind negotiation by sending a BindRequest
 with a different value in the mechanism field of SaslCredentials, or
 an AuthenticationChoice other than sasl.

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 If the client sends a BindRequest with the sasl mechanism field as an
 empty string, the server MUST return a BindResponse with the
 resultCode set to authMethodNotSupported.  This will allow the client
 to abort a negotiation if it wishes to try again with the same SASL
 mechanism.

4.2.2. Bind Response

 The Bind response is defined as follows.
      BindResponse ::= [APPLICATION 1] SEQUENCE {
           COMPONENTS OF LDAPResult,
           serverSaslCreds    [7] OCTET STRING OPTIONAL }
 BindResponse consists simply of an indication from the server of the
 status of the client's request for authentication.
 A successful Bind operation is indicated by a BindResponse with a
 resultCode set to success.  Otherwise, an appropriate result code is
 set in the BindResponse.  For BindResponse, the protocolError result
 code may be used to indicate that the version number supplied by the
 client is unsupported.
 If the client receives a BindResponse where the resultCode is set to
 protocolError, it is to assume that the server does not support this
 version of LDAP.  While the client may be able proceed with another
 version of this protocol (which may or may not require closing and
 re-establishing the transport connection), how to proceed with
 another version of this protocol is beyond the scope of this
 document.  Clients that are unable or unwilling to proceed SHOULD
 terminate the LDAP session.
 The serverSaslCreds field is used as part of a SASL-defined bind
 mechanism to allow the client to authenticate the server to which it
 is communicating, or to perform "challenge-response" authentication.
 If the client bound with the simple choice, or the SASL mechanism
 does not require the server to return information to the client, then
 this field SHALL NOT be included in the BindResponse.

4.3. Unbind Operation

 The function of the Unbind operation is to terminate an LDAP session.
 The Unbind operation is not the antithesis of the Bind operation as
 the name implies.  The naming of these operations are historical.
 The Unbind operation should be thought of as the "quit" operation.

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 The Unbind operation is defined as follows:
      UnbindRequest ::= [APPLICATION 2] NULL
 The client, upon transmission of the UnbindRequest, and the server,
 upon receipt of the UnbindRequest, are to gracefully terminate the
 LDAP session as described in Section 5.3.  Uncompleted operations are
 handled as specified in Section 3.1.

4.4. Unsolicited Notification

 An unsolicited notification is an LDAPMessage sent from the server to
 the client that is not in response to any LDAPMessage received by the
 server.  It is used to signal an extraordinary condition in the
 server or in the LDAP session between the client and the server.  The
 notification is of an advisory nature, and the server will not expect
 any response to be returned from the client.
 The unsolicited notification is structured as an LDAPMessage in which
 the messageID is zero and protocolOp is set to the extendedResp
 choice using the ExtendedResponse type (See Section 4.12).  The
 responseName field of the ExtendedResponse always contains an LDAPOID
 that is unique for this notification.
 One unsolicited notification (Notice of Disconnection) is defined in
 this document.  The specification of an unsolicited notification
 consists of:
  1. the OBJECT IDENTIFIER assigned to the notification (to be specified

in the responseName,

  1. the format of the contents of the responseValue (if any),
  1. the circumstances which will cause the notification to be sent, and
  1. the semantics of the message.

4.4.1. Notice of Disconnection

 This notification may be used by the server to advise the client that
 the server is about to terminate the LDAP session on its own
 initiative.  This notification is intended to assist clients in
 distinguishing between an exceptional server condition and a
 transient network failure.  Note that this notification is not a
 response to an Unbind requested by the client.  Uncompleted
 operations are handled as specified in Section 3.1.

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 The responseName is 1.3.6.1.4.1.1466.20036, the responseValue field
 is absent, and the resultCode is used to indicate the reason for the
 disconnection.  When the strongerAuthRequired resultCode is returned
 with this message, it indicates that the server has detected that an
 established security association between the client and server has
 unexpectedly failed or been compromised.
 Upon transmission of the Notice of Disconnection, the server
 gracefully terminates the LDAP session as described in Section 5.3.

4.5. Search Operation

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

4.5.1. Search Request

 The Search request is defined as follows:
      SearchRequest ::= [APPLICATION 3] SEQUENCE {
           baseObject      LDAPDN,
           scope           ENUMERATED {
                baseObject              (0),
                singleLevel             (1),
                wholeSubtree            (2),
                ...  },
           derefAliases    ENUMERATED {
                neverDerefAliases       (0),
                derefInSearching        (1),
                derefFindingBaseObj     (2),
                derefAlways             (3) },
           sizeLimit       INTEGER (0 ..  maxInt),
           timeLimit       INTEGER (0 ..  maxInt),
           typesOnly       BOOLEAN,
           filter          Filter,
           attributes      AttributeSelection }
      AttributeSelection ::= SEQUENCE OF selector LDAPString
                      -- The LDAPString is constrained to
                      -- <attributeSelector> in Section 4.5.1.8
      Filter ::= CHOICE {
           and             [0] SET SIZE (1..MAX) OF filter Filter,
           or              [1] SET SIZE (1..MAX) OF filter Filter,
           not             [2] Filter,

Sermersheim Standards Track [Page 20] RFC 4511 LDAPv3 June 2006

           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,
           substrings     SEQUENCE SIZE (1..MAX) OF substring CHOICE {
                initial [0] AssertionValue,  -- can occur at most once
                any     [1] AssertionValue,
                final   [2] AssertionValue } -- can occur at most once
           }
      MatchingRuleAssertion ::= SEQUENCE {
           matchingRule    [1] MatchingRuleId OPTIONAL,
           type            [2] AttributeDescription OPTIONAL,
           matchValue      [3] AssertionValue,
           dnAttributes    [4] BOOLEAN DEFAULT FALSE }
 Note that an X.500 "list"-like operation can be emulated by the
 client requesting a singleLevel Search operation with a filter
 checking for the presence of the 'objectClass' attribute, and that an
 X.500 "read"-like operation can be emulated by a baseObject Search
 operation with the same filter.  A server that provides a gateway to
 X.500 is not required to use the Read or List operations, although it
 may choose to do so, and if it does, it must provide the same
 semantics as the X.500 Search operation.

4.5.1.1. SearchRequest.baseObject

 The name of the base object entry (or possibly the root) relative to
 which the Search is to be performed.

4.5.1.2. SearchRequest.scope

 Specifies the scope of the Search to be performed.  The semantics (as
 described in [X.511]) of the defined values of this field are:
    baseObject: The scope is constrained to the entry named by
    baseObject.
    singleLevel: The scope is constrained to the immediate
    subordinates of the entry named by baseObject.

Sermersheim Standards Track [Page 21] RFC 4511 LDAPv3 June 2006

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

4.5.1.3. SearchRequest.derefAliases

 An indicator as to whether or not alias entries (as defined in
 [RFC4512]) are to be dereferenced during stages of the Search
 operation.
 The act of dereferencing an alias includes recursively dereferencing
 aliases that refer to aliases.
 Servers MUST detect looping while dereferencing aliases in order to
 prevent denial-of-service attacks of this nature.
 The semantics of the defined values of this field are:
    neverDerefAliases: Do not dereference aliases in searching or in
    locating the base object of the Search.
    derefInSearching: While searching subordinates of the base object,
    dereference any alias within the search scope.  Dereferenced
    objects become the vertices of further search scopes where the
    Search operation is also applied.  If the search scope is
    wholeSubtree, the Search continues in the subtree(s) of any
    dereferenced object.  If the search scope is singleLevel, the
    search is applied to any dereferenced objects and is not applied
    to their subordinates.  Servers SHOULD eliminate duplicate entries
    that arise due to alias dereferencing while searching.
    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.

4.5.1.4. SearchRequest.sizeLimit

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

Sermersheim Standards Track [Page 22] RFC 4511 LDAPv3 June 2006

4.5.1.5. SearchRequest.timeLimit

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

4.5.1.6. SearchRequest.typesOnly

 An indicator as to whether Search results are to contain both
 attribute descriptions and values, or just attribute descriptions.
 Setting this field to TRUE causes only attribute descriptions (and
 not values) to be returned.  Setting this field to FALSE causes both
 attribute descriptions and values to be returned.

4.5.1.7. SearchRequest.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 were explicit.)
 A server MUST evaluate filters according to the three-valued logic of
 [X.511] (1993), Clause 7.8.1.  In summary, a filter is evaluated to
 "TRUE", "FALSE", or "Undefined".  If the filter evaluates to TRUE for
 a particular entry, then the attributes of that entry are returned as
 part of the Search result (subject to any applicable access control
 restrictions).  If the filter evaluates to FALSE or Undefined, then
 the entry is ignored for the Search.
 A filter of the "and" choice is TRUE if all the filters in the SET OF
 evaluate to TRUE, FALSE if at least one filter is FALSE, and
 Undefined otherwise.  A filter of the "or" choice is FALSE if all 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.
 A filter item evaluates to Undefined when the server would not be
 able to determine whether the assertion value matches an entry.
 Examples include:

Sermersheim Standards Track [Page 23] RFC 4511 LDAPv3 June 2006

  1. An attribute description in an equalityMatch, substrings,

greaterOrEqual, lessOrEqual, approxMatch, or extensibleMatch filter

   is not recognized by the server.
  1. The attribute type does not define the appropriate matching rule.
  1. A MatchingRuleId in the extensibleMatch is not recognized by the

server or is not valid for the attribute type.

  1. The type of filtering requested is not implemented.
  1. The assertion value is invalid.
 For example, if a server did not recognize the attribute type
 shoeSize, the filters (shoeSize=*), (shoeSize=12), (shoeSize>=12),
 and (shoeSize<=12) would each evaluate to Undefined.
 Servers MUST NOT return errors if attribute descriptions or matching
 rule ids are not recognized, assertion values are invalid, or the
 assertion syntax is not supported.  More details of filter processing
 are given in Clause 7.8 of [X.511].

4.5.1.7.1. SearchRequest.filter.equalityMatch

 The matching rule for an equalityMatch filter is defined by the
 EQUALITY matching rule for the attribute type or subtype.  The filter
 is TRUE when the EQUALITY rule returns TRUE as applied to the
 attribute or subtype and the asserted value.

4.5.1.7.2. SearchRequest.filter.substrings

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

Sermersheim Standards Track [Page 24] RFC 4511 LDAPv3 June 2006

4.5.1.7.3. SearchRequest.filter.greaterOrEqual

 The matching rule for a greaterOrEqual filter is defined by the
 ORDERING matching rule for the attribute type or subtype.  The filter
 is TRUE when the ORDERING rule returns FALSE as applied to the
 attribute or subtype and the asserted value.

4.5.1.7.4. SearchRequest.filter.lessOrEqual

 The matching rules for a lessOrEqual filter are defined by the
 ORDERING and EQUALITY matching rules for the attribute type or
 subtype.  The filter is TRUE when either the ORDERING or EQUALITY
 rule returns TRUE as applied to the attribute or subtype and the
 asserted value.

4.5.1.7.5. SearchRequest.filter.present

 A present filter is TRUE when there is an attribute or subtype of the
 specified attribute description present in an entry, FALSE when no
 attribute or subtype of the specified attribute description is
 present in an entry, and Undefined otherwise.

4.5.1.7.6. SearchRequest.filter.approxMatch

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

4.5.1.7.7. SearchRequest.filter.extensibleMatch

 The fields of the extensibleMatch filter item are evaluated as
 follows:
  1. If the matchingRule field is absent, the type field MUST be

present, and an equality match is performed for that type.

  1. If the type field is absent and the matchingRule is present, the

matchValue is compared against all attributes in an entry that

   support that matchingRule.
  1. If the type field is present and the matchingRule is present, the

matchValue is compared against the specified attribute type and its

   subtypes.

Sermersheim Standards Track [Page 25] RFC 4511 LDAPv3 June 2006

  1. If the dnAttributes field is set to TRUE, the match is additionally

applied against all the AttributeValueAssertions in an entry's

   distinguished name, and it evaluates to TRUE if there is at least
   one attribute or subtype in the distinguished name for which the
   filter item evaluates to TRUE.  The dnAttributes field is present
   to alleviate the need for multiple versions of generic matching
   rules (such as word matching), where one applies to entries and
   another applies to entries and DN attributes as well.
 The matchingRule used for evaluation determines the syntax for the
 assertion value.  Once the matchingRule and attribute(s) have been
 determined, the filter item evaluates to TRUE if it matches at least
 one attribute type or subtype in the entry, FALSE if it does not
 match any attribute type or subtype in the entry, and Undefined if
 the matchingRule is not recognized, the matchingRule is unsuitable
 for use with the specified type, or the assertionValue is invalid.

4.5.1.8. SearchRequest.attributes

 A selection list of the attributes to be returned from each entry
 that matches the search filter.  Attributes that are subtypes of
 listed attributes are implicitly included.  LDAPString values of this
 field are constrained to the following Augmented Backus-Naur Form
 (ABNF) [RFC4234]:
    attributeSelector = attributedescription / selectorspecial
    selectorspecial = noattrs / alluserattrs
    noattrs = %x31.2E.31 ; "1.1"
    alluserattrs = %x2A ; asterisk ("*")
    The <attributedescription> production is defined in Section 2.5 of
    [RFC4512].
    There are three special cases that may appear in the attributes
    selection list:
    1. An empty list with no attributes requests the return of all
       user attributes.
    2. A list containing "*" (with zero or more attribute
       descriptions) requests the return of all user attributes in
       addition to other listed (operational) attributes.

Sermersheim Standards Track [Page 26] RFC 4511 LDAPv3 June 2006

    3. A list containing only the OID "1.1" indicates that no
       attributes are to be returned.  If "1.1" is provided with other
       attributeSelector values, the "1.1" attributeSelector is
       ignored.  This OID was chosen because it does not (and can not)
       correspond to any attribute in use.
 Client implementors should note that even if all user attributes are
 requested, some attributes and/or attribute values of the entry may
 not be included in Search results due to access controls or other
 restrictions.  Furthermore, servers will not return operational
 attributes, such as objectClasses or attributeTypes, unless they are
 listed by name.  Operational attributes are described in [RFC4512].
 Attributes are returned at most once in an entry.  If an attribute
 description is named more than once in the list, the subsequent names
 are ignored.  If an attribute description in the list is not
 recognized, it is ignored by the server.

4.5.2. Search Result

 The results of the Search operation are returned as zero or more
 SearchResultEntry and/or SearchResultReference messages, followed by
 a single SearchResultDone message.
      SearchResultEntry ::= [APPLICATION 4] SEQUENCE {
           objectName      LDAPDN,
           attributes      PartialAttributeList }
      PartialAttributeList ::= SEQUENCE OF
                           partialAttribute PartialAttribute
      SearchResultReference ::= [APPLICATION 19] SEQUENCE
                                SIZE (1..MAX) OF uri URI
      SearchResultDone ::= [APPLICATION 5] LDAPResult
 Each SearchResultEntry represents an entry found during the Search.
 Each SearchResultReference represents an area not yet explored during
 the Search.  The SearchResultEntry and SearchResultReference messages
 may come in any order.  Following all the SearchResultReference and
 SearchResultEntry responses, the server returns a SearchResultDone
 response, which contains an indication of success or details any
 errors that have occurred.
 Each entry returned in a SearchResultEntry will contain all
 appropriate attributes as specified in the attributes field of the
 Search Request, subject to access control and other administrative
 policy.  Note that the PartialAttributeList may hold zero elements.

Sermersheim Standards Track [Page 27] RFC 4511 LDAPv3 June 2006

 This may happen when none of the attributes of an entry were
 requested or could be returned.  Note also that the partialAttribute
 vals set may hold zero elements.  This may happen when typesOnly is
 requested, access controls prevent the return of values, or other
 reasons.
 Some attributes may be constructed by the server and appear in a
 SearchResultEntry attribute list, although they are not stored
 attributes of an entry.  Clients SHOULD NOT assume that all
 attributes can be modified, even if this is permitted by access
 control.
 If the server's schema defines short names [RFC4512] for an attribute
 type, then the server SHOULD use one of those names in attribute
 descriptions for that attribute type (in preference to using the
 <numericoid> [RFC4512] format of the attribute type's object
 identifier).  The server SHOULD NOT use the short name if that name
 is known by the server to be ambiguous, or if it is otherwise likely
 to cause interoperability problems.

4.5.3. Continuation References in the Search Result

 If the server was able to locate the entry referred to by the
 baseObject but was unable or unwilling to search one or more non-
 local entries, the server may return one or more
 SearchResultReference messages, each containing a reference to
 another set of servers for continuing the operation.  A server MUST
 NOT return any SearchResultReference messages if it has not located
 the baseObject and thus has not searched any entries.  In this case,
 it would return a SearchResultDone containing either a referral or
 noSuchObject result code (depending on the server's knowledge of the
 entry named in the baseObject).
 If a server holds a copy or partial copy of the subordinate naming
 context (Section 5 of [RFC4512]), it may use the search filter to
 determine whether or not to return a SearchResultReference response.
 Otherwise, SearchResultReference responses are always returned when
 in scope.
 The SearchResultReference is of the same data type as the Referral.
 If the client wishes to progress the Search, it issues a new Search
 operation for each SearchResultReference that is returned.  If
 multiple URIs are present, the client assumes that any supported URI
 may be used to progress the operation.

Sermersheim Standards Track [Page 28] RFC 4511 LDAPv3 June 2006

 Clients that follow search continuation references MUST ensure that
 they do not loop between servers.  They MUST NOT repeatedly contact
 the same server for the same request with the same parameters.  Some
 clients use a counter that is incremented each time search result
 reference handling occurs for an operation, and these kinds of
 clients MUST be able to handle at least ten nested referrals while
 progressing the operation.
 Note that the Abandon operation described in Section 4.11 applies
 only to a particular operation sent at the LDAP message layer between
 a client and server.  The client must individually abandon subsequent
 Search operations it wishes to.
 A URI for a server implementing LDAP and accessible via TCP/IP (v4 or
 v6) [RFC793][RFC791] is written as an LDAP URL according to
 [RFC4516].
 SearchResultReference values that are LDAP URLs follow these rules:
  1. The <dn> part of the LDAP URL MUST be present, with the new target

object name. The client uses this name when following the

   reference.
  1. Some servers (e.g., participating in distributed indexing) may

provide a different filter in the LDAP URL.

  1. If the <filter> part of the LDAP URL is present, the client uses

this filter in its next request to progress this Search, and if it

   is not present the client uses the same filter as it used for that
   Search.
  1. If the originating search scope was singleLevel, the <scope> part

of the LDAP URL will be "base".

  1. It is RECOMMENDED that the <scope> part be present to avoid

ambiguity. In the absence of a <scope> part, the scope of the

   original Search request is assumed.
  1. Other aspects of the new Search request may be the same as or

different from the Search request that generated the

   SearchResultReference.
  1. The name of an unexplored subtree in a SearchResultReference need

not be subordinate to the base object.

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

Sermersheim Standards Track [Page 29] RFC 4511 LDAPv3 June 2006

 UTF-8-encoded characters appearing in the string representation of a
 DN, search filter, or other fields of the referral value may not be
 legal for URIs (e.g., spaces) and MUST be escaped using the % method
 in [RFC3986].

4.5.3.1. Examples

 For example, suppose the contacted server (hosta) holds the entry
 <DC=Example,DC=NET> and the entry <CN=Manager,DC=Example,DC=NET>.  It
 knows that both LDAP servers (hostb) and (hostc) hold
 <OU=People,DC=Example,DC=NET> (one is the master and the other server
 a shadow), and that LDAP-capable server (hostd) holds the subtree
 <OU=Roles,DC=Example,DC=NET>.  If a wholeSubtree Search of
 <DC=Example,DC=NET> is requested to the contacted server, it may
 return the following:
   SearchResultEntry for DC=Example,DC=NET
   SearchResultEntry for CN=Manager,DC=Example,DC=NET
   SearchResultReference {
     ldap://hostb/OU=People,DC=Example,DC=NET??sub
     ldap://hostc/OU=People,DC=Example,DC=NET??sub }
   SearchResultReference {
     ldap://hostd/OU=Roles,DC=Example,DC=NET??sub }
   SearchResultDone (success)
 Client implementors should note that when following a
 SearchResultReference, additional SearchResultReference may be
 generated.  Continuing the example, if the client contacted the
 server (hostb) and issued the Search request for the subtree
 <OU=People,DC=Example,DC=NET>, the server might respond as follows:
   SearchResultEntry for OU=People,DC=Example,DC=NET
   SearchResultReference {
     ldap://hoste/OU=Managers,OU=People,DC=Example,DC=NET??sub }
   SearchResultReference {
     ldap://hostf/OU=Consultants,OU=People,DC=Example,DC=NET??sub }
   SearchResultDone (success)
 Similarly, if a singleLevel Search of <DC=Example,DC=NET> is
 requested to the contacted server, it may return the following:
   SearchResultEntry for CN=Manager,DC=Example,DC=NET
   SearchResultReference {
     ldap://hostb/OU=People,DC=Example,DC=NET??base
     ldap://hostc/OU=People,DC=Example,DC=NET??base }
   SearchResultReference {
     ldap://hostd/OU=Roles,DC=Example,DC=NET??base }
   SearchResultDone (success)

Sermersheim Standards Track [Page 30] RFC 4511 LDAPv3 June 2006

 If the contacted server does not hold the base object for the Search,
 but has knowledge of its possible location, then it may return a
 referral to the client.  In this case, if the client requests a
 subtree Search of <DC=Example,DC=ORG> to hosta, the server returns a
 SearchResultDone containing a referral.
   SearchResultDone (referral) {
     ldap://hostg/DC=Example,DC=ORG??sub }

4.6. Modify Operation

 The Modify operation allows a client to request that a modification
 of an entry be performed on its behalf by a server.  The Modify
 Request is defined as follows:
      ModifyRequest ::= [APPLICATION 6] SEQUENCE {
           object          LDAPDN,
           changes         SEQUENCE OF change SEQUENCE {
                operation       ENUMERATED {
                     add     (0),
                     delete  (1),
                     replace (2),
                     ...  },
                modification    PartialAttribute } }
 Fields of the Modify Request are:
  1. object: The value of this field contains the name of the entry to

be modified. The server SHALL NOT perform any alias dereferencing

   in determining the object to be modified.
  1. changes: A list of modifications to be performed on the entry. The

entire list of modifications MUST be performed in the order they

   are listed as a single atomic operation.  While individual
   modifications may violate certain aspects of the directory schema
   (such as the object class definition and Directory Information Tree
   (DIT) content rule), the resulting entry after the entire list of
   modifications is performed MUST conform to the requirements of the
   directory model and controlling schema [RFC4512].
  1. operation: Used to specify the type of modification being

performed. Each operation type acts on the following

      modification.  The values of this field have the following
      semantics, respectively:
         add: add values listed to the modification attribute,
         creating the attribute if necessary.

Sermersheim Standards Track [Page 31] RFC 4511 LDAPv3 June 2006

         delete: delete values listed from the modification attribute.
         If no values are listed, or if all current values of the
         attribute are listed, the entire attribute is removed.
         replace: replace all existing values of the modification
         attribute with the new values listed, creating the attribute
         if it did not already exist.  A replace with no value will
         delete the entire attribute if it exists, and it is ignored
         if the attribute does not exist.
  1. modification: A PartialAttribute (which may have an empty SET

of vals) used to hold the attribute type or attribute type and

      values being modified.
 Upon receipt of a Modify Request, the server attempts to perform the
 necessary modifications to the DIT and returns the result in a Modify
 Response, defined as follows:
      ModifyResponse ::= [APPLICATION 7] LDAPResult
 The server will return to the client a single Modify Response
 indicating either the successful completion of the DIT modification,
 or the reason that the modification failed.  Due to the requirement
 for atomicity in applying the list of modifications in the Modify
 Request, the client may expect that no modifications of the DIT have
 been performed if the Modify Response received indicates any sort of
 error, and that all requested modifications have been performed if
 the Modify Response indicates successful completion of the Modify
 operation.  Whether or not the modification was applied cannot be
 determined by the client if the Modify Response was not received
 (e.g., the LDAP session was terminated or the Modify operation was
 abandoned).
 Servers MUST ensure that entries conform to user and system schema
 rules or other data model constraints.  The Modify operation cannot
 be used to remove from an entry any of its distinguished values,
 i.e., those values which form the entry's relative distinguished
 name.  An attempt to do so will result in the server returning the
 notAllowedOnRDN result code.  The Modify DN operation described in
 Section 4.9 is used to rename an entry.
 For attribute types that specify no equality matching, the rules in
 Section 2.5.1 of [RFC4512] are followed.
 Note that due to the simplifications made in LDAP, there is not a
 direct mapping of the changes in an LDAP ModifyRequest onto the
 changes of a DAP ModifyEntry operation, and different implementations

Sermersheim Standards Track [Page 32] RFC 4511 LDAPv3 June 2006

 of LDAP-DAP gateways may use different means of representing the
 change.  If successful, the final effect of the operations on the
 entry MUST be identical.

4.7. Add Operation

 The Add operation allows a client to request the addition of an entry
 into the Directory.  The Add Request is defined as follows:
      AddRequest ::= [APPLICATION 8] SEQUENCE {
           entry           LDAPDN,
           attributes      AttributeList }
      AttributeList ::= SEQUENCE OF attribute Attribute
 Fields of the Add Request are:
  1. entry: the name of the entry to be added. The server SHALL NOT

dereference any aliases in locating the entry to be added.

  1. attributes: the list of attributes that, along with those from the

RDN, make up the content of the entry being added. Clients MAY or

   MAY NOT include the RDN attribute(s) in this list.  Clients MUST
   NOT supply NO-USER-MODIFICATION attributes such as the
   createTimestamp or creatorsName attributes, since the server
   maintains these automatically.
 Servers MUST ensure that entries conform to user and system schema
 rules or other data model constraints.  For attribute types that
 specify no equality matching, the rules in Section 2.5.1 of [RFC4512]
 are followed (this applies to the naming attribute in addition to any
 multi-valued attributes being added).
 The entry named in the entry field of the AddRequest MUST NOT exist
 for the AddRequest to succeed.  The immediate superior (parent) of an
 object or alias entry to be added MUST exist.  For example, if the
 client attempted to add <CN=JS,DC=Example,DC=NET>, the
 <DC=Example,DC=NET> entry did not exist, and the <DC=NET> entry did
 exist, then the server would return the noSuchObject result code with
 the matchedDN field containing <DC=NET>.
 Upon receipt of an Add Request, a server will attempt to add the
 requested entry.  The result of the Add attempt will be returned to
 the client in the Add Response, defined as follows:
      AddResponse ::= [APPLICATION 9] LDAPResult

Sermersheim Standards Track [Page 33] RFC 4511 LDAPv3 June 2006

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

4.8. Delete Operation

 The Delete operation allows a client to request the removal of an
 entry from the Directory.  The Delete Request is defined as follows:
      DelRequest ::= [APPLICATION 10] LDAPDN
 The Delete Request consists of the name of the entry to be deleted.
 The server SHALL NOT dereference aliases while resolving the name of
 the target entry to be removed.
 Only leaf entries (those with no subordinate entries) can be deleted
 with this operation.
 Upon receipt of a Delete Request, a server will attempt to perform
 the entry removal requested and return the result in the Delete
 Response defined as follows:
      DelResponse ::= [APPLICATION 11] LDAPResult

4.9. Modify DN Operation

 The Modify DN operation allows a client to change the Relative
 Distinguished Name (RDN) of an entry in the Directory and/or to move
 a subtree of entries to a new location in the Directory.  The Modify
 DN Request is defined as follows:
      ModifyDNRequest ::= [APPLICATION 12] SEQUENCE {
           entry           LDAPDN,
           newrdn          RelativeLDAPDN,
           deleteoldrdn    BOOLEAN,
           newSuperior     [0] LDAPDN OPTIONAL }
 Fields of the Modify DN Request are:
  1. entry: the name of the entry to be changed. This entry may or may

not have subordinate entries.

  1. newrdn: the new RDN of the entry. The value of the old RDN is

supplied when moving the entry to a new superior without changing

   its RDN.  Attribute values of the new RDN not matching any
   attribute value of the entry are added to the entry, and an
   appropriate error is returned if this fails.

Sermersheim Standards Track [Page 34] RFC 4511 LDAPv3 June 2006

  1. deleteoldrdn: a boolean field that controls whether the old RDN

attribute values are to be retained as attributes of the entry or

   deleted from the entry.
  1. newSuperior: if present, this is the name of an existing object

entry that becomes the immediate superior (parent) of the

   existing entry.
 The server SHALL NOT dereference any aliases in locating the objects
 named in entry or newSuperior.
 Upon receipt of a ModifyDNRequest, a server will attempt to perform
 the name change and return the result in the Modify DN Response,
 defined as follows:
      ModifyDNResponse ::= [APPLICATION 13] LDAPResult
 For example, if the entry named in the entry field was <cn=John
 Smith,c=US>, the newrdn field was <cn=John Cougar Smith>, and the
 newSuperior field was absent, then this operation would attempt to
 rename the entry as <cn=John Cougar Smith,c=US>.  If there was
 already an entry with that name, the operation would fail with the
 entryAlreadyExists result code.
 Servers MUST ensure that entries conform to user and system schema
 rules or other data model constraints.  For attribute types that
 specify no equality matching, the rules in Section 2.5.1 of [RFC4512]
 are followed (this pertains to newrdn and deleteoldrdn).
 The object named in newSuperior MUST exist.  For example, if the
 client attempted to add <CN=JS,DC=Example,DC=NET>, the
 <DC=Example,DC=NET> entry did not exist, and the <DC=NET> entry did
 exist, then the server would return the noSuchObject result code with
 the matchedDN field containing <DC=NET>.
 If the deleteoldrdn field is TRUE, the attribute values forming the
 old RDN (but not the new RDN) are deleted from the entry.  If the
 deleteoldrdn field is FALSE, the attribute values forming the old RDN
 will be retained as non-distinguished attribute values of the entry.
 Note that X.500 restricts the ModifyDN operation to affect only
 entries that are contained within a single server.  If the LDAP
 server is mapped onto DAP, then this restriction will apply, and the
 affectsMultipleDSAs result code will be returned if this error
 occurred.  In general, clients MUST NOT expect to be able to perform
 arbitrary movements of entries and subtrees between servers or
 between naming contexts.

Sermersheim Standards Track [Page 35] RFC 4511 LDAPv3 June 2006

4.10. Compare Operation

 The Compare operation allows a client to compare an assertion value
 with the values of a particular attribute in a particular entry in
 the Directory.  The Compare Request is defined as follows:
      CompareRequest ::= [APPLICATION 14] SEQUENCE {
           entry           LDAPDN,
           ava             AttributeValueAssertion }
 Fields of the Compare Request are:
  1. entry: the name of the entry to be compared. The server SHALL NOT

dereference any aliases in locating the entry to be compared.

  1. ava: holds the attribute value assertion to be compared.
 Upon receipt of a Compare Request, a server will attempt to perform
 the requested comparison and return the result in the Compare
 Response, defined as follows:
      CompareResponse ::= [APPLICATION 15] LDAPResult
 The resultCode is set to compareTrue, compareFalse, or an appropriate
 error.  compareTrue indicates that the assertion value in the ava
 field matches a value of the attribute or subtype according to the
 attribute's EQUALITY matching rule.  compareFalse indicates that the
 assertion value in the ava field and the values of the attribute or
 subtype did not match.  Other result codes indicate either that the
 result of the comparison was Undefined (Section 4.5.1.7), or that
 some error occurred.
 Note that some directory systems may establish access controls that
 permit the values of certain attributes (such as userPassword) to be
 compared but not interrogated by other means.

4.11. Abandon Operation

 The function of the Abandon operation is to allow a client to request
 that the server abandon an uncompleted operation.  The Abandon
 Request is defined as follows:
      AbandonRequest ::= [APPLICATION 16] MessageID
 The MessageID is that of an operation that was requested earlier at
 this LDAP message layer.  The Abandon request itself has its own
 MessageID.  This is distinct from the MessageID of the earlier
 operation being abandoned.

Sermersheim Standards Track [Page 36] RFC 4511 LDAPv3 June 2006

 There is no response defined in the Abandon operation.  Upon receipt
 of an AbandonRequest, the server MAY abandon the operation identified
 by the MessageID.  Since the client cannot tell the difference
 between a successfully abandoned operation and an uncompleted
 operation, the application of the Abandon operation is limited to
 uses where the client does not require an indication of its outcome.
 Abandon, Bind, Unbind, and StartTLS operations cannot be abandoned.
 In the event that a server receives an Abandon Request on a Search
 operation in the midst of transmitting responses to the Search, that
 server MUST cease transmitting entry responses to the abandoned
 request immediately, and it MUST NOT send the SearchResultDone.  Of
 course, the server MUST ensure that only properly encoded LDAPMessage
 PDUs are transmitted.
 The ability to abandon other (particularly update) operations is at
 the discretion of the server.
 Clients should not send Abandon requests for the same operation
 multiple times, and they MUST also be prepared to receive results
 from operations they have abandoned (since these might have been in
 transit when the Abandon was requested or might not be able to be
 abandoned).
 Servers MUST discard Abandon requests for messageIDs they do not
 recognize, for operations that cannot be abandoned, and for
 operations that have already been abandoned.

4.12. Extended Operation

 The Extended operation allows additional operations to be defined for
 services not already available in the protocol; for example, to Add
 operations to install transport layer security (see Section 4.14).
 The Extended operation allows clients to make requests and receive
 responses with predefined syntaxes and semantics.  These may be
 defined in RFCs or be private to particular implementations.
 Each Extended operation consists of an Extended request and an
 Extended response.
      ExtendedRequest ::= [APPLICATION 23] SEQUENCE {
           requestName      [0] LDAPOID,
           requestValue     [1] OCTET STRING OPTIONAL }

Sermersheim Standards Track [Page 37] RFC 4511 LDAPv3 June 2006

 The requestName is a dotted-decimal representation of the unique
 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 an
 ExtendedResponse.
      ExtendedResponse ::= [APPLICATION 24] SEQUENCE {
           COMPONENTS OF LDAPResult,
           responseName     [10] LDAPOID OPTIONAL,
           responseValue    [11] OCTET STRING OPTIONAL }
 The responseName field, when present, contains an LDAPOID that is
 unique for this extended operation or response.  This field is
 optional (even when the extension specification defines an LDAPOID
 for use in this field).  The field will be absent whenever the server
 is unable or unwilling to determine the appropriate LDAPOID to
 return, for instance, when the requestName cannot be parsed or its
 value is not recognized.
 Where the requestName is not recognized, the server returns
 protocolError.  (The server may return protocolError in other cases.)
 The requestValue and responseValue fields contain information
 associated with the operation.  The format of these fields is defined
 by the specification of the Extended operation.  Implementations MUST
 be prepared to handle arbitrary contents of these fields, including
 zero bytes.  Values that are defined in terms of ASN.1 and BER-
 encoded according to Section 5.1 also follow the extensibility rules
 in Section 4.
 Servers list the requestName of Extended Requests they recognize in
 the 'supportedExtension' attribute in the root DSE (Section 5.1 of
 [RFC4512]).
 Extended operations may be specified in other documents.  The
 specification of an Extended operation consists of:
  1. the OBJECT IDENTIFIER assigned to the requestName,
  1. the OBJECT IDENTIFIER (if any) assigned to the responseName (note

that the same OBJECT IDENTIFIER may be used for both the

   requestName and responseName),

Sermersheim Standards Track [Page 38] RFC 4511 LDAPv3 June 2006

  1. the format of the contents of the requestValue and responseValue

(if any), and

  1. the semantics of the operation.

4.13. IntermediateResponse Message

 While the Search operation provides a mechanism to return multiple
 response messages for a single Search request, other operations, by
 nature, do not provide for multiple response messages.
 The IntermediateResponse message provides a general mechanism for
 defining single-request/multiple-response operations in LDAP.  This
 message is intended to be used in conjunction with the Extended
 operation to define new single-request/multiple-response operations
 or in conjunction with a control when extending existing LDAP
 operations in a way that requires them to return Intermediate
 response information.
 It is intended that the definitions and descriptions of Extended
 operations and controls that make use of the IntermediateResponse
 message will define the circumstances when an IntermediateResponse
 message can be sent by a server and the associated meaning of an
 IntermediateResponse message sent in a particular circumstance.
      IntermediateResponse ::= [APPLICATION 25] SEQUENCE {
              responseName     [0] LDAPOID OPTIONAL,
              responseValue    [1] OCTET STRING OPTIONAL }
 IntermediateResponse messages SHALL NOT be returned to the client
 unless the client issues a request that specifically solicits their
 return.  This document defines two forms of solicitation: Extended
 operation and request control.  IntermediateResponse messages are
 specified in documents describing the manner in which they are
 solicited (i.e., in the Extended operation or request control
 specification that uses them).  These specifications include:
  1. the OBJECT IDENTIFIER (if any) assigned to the responseName,
  1. the format of the contents of the responseValue (if any), and
  1. the semantics associated with the IntermediateResponse message.
 Extensions that allow the return of multiple types of
 IntermediateResponse messages SHALL identify those types using unique
 responseName values (note that one of these may specify no value).

Sermersheim Standards Track [Page 39] RFC 4511 LDAPv3 June 2006

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

4.13.1. Usage with LDAP ExtendedRequest and ExtendedResponse

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

4.13.2. Usage with LDAP Request Controls

 A control's semantics may include the return of zero or more
 IntermediateResponse messages prior to returning the final result
 code for the operation.  One or more kinds of IntermediateResponse
 messages may be sent in response to a request control.
 All IntermediateResponse messages associated with request controls
 SHALL include a responseName.  This requirement ensures that the
 client can correctly identify the source of IntermediateResponse
 messages when:
  1. two or more controls using IntermediateResponse messages are

included in a request for any LDAP operation or

  1. one or more controls using IntermediateResponse messages are

included in a request with an LDAP Extended operation that uses

   IntermediateResponse messages.

4.14. StartTLS Operation

 The Start Transport Layer Security (StartTLS) operation's purpose is
 to initiate installation of a TLS layer.  The StartTLS operation is
 defined using the Extended operation mechanism described in Section
 4.12.

4.14.1. StartTLS Request

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

Sermersheim Standards Track [Page 40] RFC 4511 LDAPv3 June 2006

 The client MUST NOT send any LDAP PDUs at this LDAP message layer
 following this request until it receives a StartTLS Extended response
 and, in the case of a successful response, completes TLS
 negotiations.
 Detected sequencing problems (particularly those detailed in Section
 3.1.1 of [RFC4513]) result in the resultCode being set to
 operationsError.
 If the server does not support TLS (whether by design or by current
 configuration), it returns with the resultCode set to protocolError
 as described in Section 4.12.

4.14.2. StartTLS Response

 When a StartTLS request is received, servers supporting the operation
 MUST return a StartTLS response message to the requestor.  The
 responseName is "1.3.6.1.4.1.1466.20037" when provided (see Section
 4.12).  The responseValue is always absent.
 If the server is willing and able to negotiate TLS, it returns the
 StartTLS response with the resultCode set to success.  Upon client
 receipt of a successful StartTLS response, protocol peers may
 commence with TLS negotiation as discussed in Section 3 of [RFC4513].
 If the server is otherwise unwilling or unable to perform this
 operation, the server is to return an appropriate result code
 indicating the nature of the problem.  For example, if the TLS
 subsystem is not presently available, the server may indicate this by
 returning with the resultCode set to unavailable.  In cases where a
 non-success result code is returned, the LDAP session is left without
 a TLS layer.

4.14.3. Removal of the TLS Layer

 Either the client or server MAY remove the TLS layer and leave the
 LDAP message layer intact by sending and receiving a TLS closure
 alert.
 The initiating protocol peer sends the TLS closure alert and MUST
 wait until it receives a TLS closure alert from the other peer before
 sending further LDAP PDUs.
 When a protocol peer receives the initial TLS closure alert, it may
 choose to allow the LDAP message layer to remain intact.  In this
 case, it MUST immediately transmit a TLS closure alert.  Following
 this, it MAY send and receive LDAP PDUs.

Sermersheim Standards Track [Page 41] RFC 4511 LDAPv3 June 2006

 Protocol peers MAY terminate the LDAP session after sending or
 receiving a TLS closure alert.

5. Protocol Encoding, Connection, and Transfer

 This protocol is designed to run over connection-oriented, reliable
 transports, where the data stream is divided into octets (8-bit
 units), with each octet and each bit being significant.
 One underlying service, LDAP over TCP, is defined in Section 5.2.
 This service is generally applicable to applications providing or
 consuming X.500-based directory services on the Internet.  This
 specification was generally written with the TCP mapping in mind.
 Specifications detailing other mappings may encounter various
 obstacles.
 Implementations of LDAP over TCP MUST implement the mapping as
 described in Section 5.2.
 This table illustrates the relationship among the different layers
 involved in an exchange between two protocol peers:
             +----------------------+
             |  LDAP message layer  |
             +----------------------+ > LDAP PDUs
             +----------------------+ < data
             |      SASL layer      |
             +----------------------+ > SASL-protected data
             +----------------------+ < data
             |       TLS layer      |
 Application +----------------------+ > TLS-protected data
 ------------+----------------------+ < data
   Transport | transport connection |
             +----------------------+

5.1. Protocol Encoding

 The protocol elements of LDAP SHALL be encoded for exchange using the
 Basic Encoding Rules [BER] of [ASN.1] with the following
 restrictions:
  1. Only the definite form of length encoding is used.
  1. OCTET STRING values are encoded in the primitive form only.
  1. If the value of a BOOLEAN type is true, the encoding of the value

octet is set to hex "FF".

Sermersheim Standards Track [Page 42] RFC 4511 LDAPv3 June 2006

  1. If a value of a type is its default value, it is absent. Only some

BOOLEAN and INTEGER types have default values in this protocol

   definition.
 These restrictions are meant to ease the overhead of encoding and
 decoding certain elements in BER.
 These restrictions do not apply to ASN.1 types encapsulated inside of
 OCTET STRING values, such as attribute values, unless otherwise
 stated.

5.2. Transmission Control Protocol (TCP)

 The encoded LDAPMessage PDUs are mapped directly onto the TCP
 [RFC793] bytestream using the BER-based encoding described in Section
 5.1.  It is recommended that server implementations running over the
 TCP provide a protocol listener on the Internet Assigned Numbers
 Authority (IANA)-assigned LDAP port, 389 [PortReg].  Servers may
 instead provide a listener on a different port number.  Clients MUST
 support contacting servers on any valid TCP port.

5.3. Termination of the LDAP session

 Termination of the LDAP session is typically initiated by the client
 sending an UnbindRequest (Section 4.3), or by the server sending a
 Notice of Disconnection (Section 4.4.1).  In these cases, each
 protocol peer gracefully terminates the LDAP session by ceasing
 exchanges at the LDAP message layer, tearing down any SASL layer,
 tearing down any TLS layer, and closing the transport connection.
 A protocol peer may determine that the continuation of any
 communication would be pernicious, and in this case, it may abruptly
 terminate the session by ceasing communication and closing the
 transport connection.
 In either case, when the LDAP session is terminated, uncompleted
 operations are handled as specified in Section 3.1.

6. Security Considerations

 This version of the protocol provides facilities for simple
 authentication using a cleartext password, as well as any SASL
 [RFC4422] mechanism.  Installing SASL and/or TLS layers can provide
 integrity and other data security services.
 It is also permitted that the server can return its credentials to
 the client, if it chooses to do so.

Sermersheim Standards Track [Page 43] RFC 4511 LDAPv3 June 2006

 Use of cleartext password is strongly discouraged where the
 underlying transport service cannot guarantee confidentiality and may
 result in disclosure of the password to unauthorized parties.
 Servers are encouraged to prevent directory modifications by clients
 that have authenticated anonymously [RFC4513].
 Security considerations for authentication methods, SASL mechanisms,
 and TLS are described in [RFC4513].
 Note that SASL authentication exchanges do not provide data
 confidentiality or integrity protection for the version or name
 fields of the BindRequest or the resultCode, diagnosticMessage, or
 referral fields of the BindResponse, nor for any information
 contained in controls attached to Bind requests or responses.  Thus,
 information contained in these fields SHOULD NOT be relied on unless
 it is otherwise protected (such as by establishing protections at the
 transport layer).
 Implementors should note that various security factors (including
 authentication and authorization information and data security
 services) may change during the course of the LDAP session or even
 during the performance of a particular operation.  For instance,
 credentials could expire, authorization identities or access controls
 could change, or the underlying security layer(s) could be replaced
 or terminated.  Implementations should be robust in the handling of
 changing security factors.
 In some cases, it may be appropriate to continue the operation even
 in light of security factor changes.  For instance, it may be
 appropriate to continue an Abandon operation regardless of the
 change, or to continue an operation when the change upgraded (or
 maintained) the security factor.  In other cases, it may be
 appropriate to fail or alter the processing of the operation.  For
 instance, if confidential protections were removed, it would be
 appropriate either to fail a request to return sensitive data or,
 minimally, to exclude the return of sensitive data.
 Implementations that 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 that prevent the return of entries or attributes in
 Search results except to particular authenticated clients.  For
 example, caches could serve result information only to the client
 whose request caused it to be in the cache.

Sermersheim Standards Track [Page 44] RFC 4511 LDAPv3 June 2006

 Servers may return referrals or Search result references that
 redirect clients to peer servers.  It is possible for a rogue
 application to inject such referrals into the data stream in an
 attempt to redirect a client to a rogue server.  Clients are advised
 to be aware of this and possibly reject referrals when
 confidentiality measures are not in place.  Clients are advised to
 reject referrals from the StartTLS operation.
 The matchedDN and diagnosticMessage fields, as well as some
 resultCode values (e.g., attributeOrValueExists and
 entryAlreadyExists), could disclose the presence or absence of
 specific data in the directory that is subject to access and other
 administrative controls.  Server implementations should restrict
 access to protected information equally under both normal and error
 conditions.
 Protocol peers MUST be prepared to handle invalid and arbitrary-
 length protocol encodings.  Invalid protocol encodings include: BER
 encoding exceptions, format string and UTF-8 encoding exceptions,
 overflow exceptions, integer value exceptions, and binary mode on/off
 flag exceptions.  The LDAPv3 PROTOS [PROTOS-LDAP] test suite provides
 excellent examples of these exceptions and test cases used to
 discover flaws.
 In the event that a protocol peer senses an attack that in its nature
 could cause damage due to further communication at any layer in the
 LDAP session, the protocol peer should abruptly terminate the LDAP
 session as described in Section 5.3.

7. Acknowledgements

 This document is based on RFC 2251 by Mark Wahl, Tim Howes, and Steve
 Kille.  RFC 2251 was a product of the IETF ASID Working Group.
 It is also based on RFC 2830 by Jeff Hodges, RL "Bob" Morgan, and
 Mark Wahl.  RFC 2830 was a product of the IETF LDAPEXT Working Group.
 It is also based on RFC 3771 by Roger Harrison and Kurt Zeilenga.
 RFC 3771 was an individual submission to the IETF.
 This document is a product of the IETF LDAPBIS Working Group.
 Significant contributors of technical review and content include Kurt
 Zeilenga, Steven Legg, and Hallvard Furuseth.

Sermersheim Standards Track [Page 45] RFC 4511 LDAPv3 June 2006

8. Normative References

 [ASN.1]       ITU-T Recommendation X.680 (07/2002) | ISO/IEC 8824-
               1:2002 "Information Technology - Abstract Syntax
               Notation One (ASN.1): Specification of basic notation".
 [BER]         ITU-T Rec. X.690 (07/2002) | ISO/IEC 8825-1:2002,
               "Information technology - ASN.1 encoding rules:
               Specification of Basic Encoding Rules (BER), Canonical
               Encoding Rules (CER) and Distinguished Encoding Rules
               (DER)", 2002.
 [ISO10646]    Universal Multiple-Octet Coded Character Set (UCS) -
               Architecture and Basic Multilingual Plane, ISO/IEC
               10646-1 : 1993.
 [RFC791]      Postel, J., "Internet Protocol", STD 5, RFC 791,
               September 1981.
 [RFC793]      Postel, J., "Transmission Control Protocol", STD 7, RFC
               793, September 1981.
 [RFC2119]     Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC3454]     Hoffman P. and M. Blanchet, "Preparation of
               Internationalized Strings ('stringprep')", RFC 3454,
               December 2002.
 [RFC3629]     Yergeau, F., "UTF-8, a transformation format of ISO
               10646", STD 63, RFC 3629, November 2003.
 [RFC3986]     Berners-Lee, T., Fielding, R., and L. Masinter,
               "Uniform Resource Identifier (URI): Generic Syntax",
               STD 66, RFC 3986, January 2005.
 [RFC4013]     Zeilenga, K., "SASLprep: Stringprep Profile for User
               Names and Passwords", RFC 4013, February 2005.
 [RFC4234]     Crocker, D. and P. Overell, "Augmented BNF for Syntax
               Specifications: ABNF", RFC 4234, October 2005.
 [RFC4346]     Dierks, T. and E. Rescorla, "The TLS Protocol Version
               1.1", RFC 4346, March 2006.
 [RFC4422]     Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple
               Authentication and Security Layer (SASL)", RFC 4422,
               June 2006.

Sermersheim Standards Track [Page 46] RFC 4511 LDAPv3 June 2006

 [RFC4510]     Zeilenga, K., Ed., "Lightweight Directory Access
               Protocol (LDAP): Technical Specification Road Map", RFC
               4510, June 2006.
 [RFC4512]     Zeilenga, K., Lightweight Directory Access Protocol
               (LDAP): Directory Information Models", RFC 4512, June
               2006.
 [RFC4513]     Harrison, R., Ed., "Lightweight Directory Access
               Protocol (LDAP): Authentication Methods and Security
               Mechanisms", RFC 4513, June 2006.
 [RFC4514]     Zeilenga, K., Ed., "Lightweight Directory Access
               Protocol (LDAP): String Representation of Distinguished
               Names", RFC 4514, June 2006.
 [RFC4516]     Smith, M., Ed. and T. Howes, "Lightweight Directory
               Access Protocol (LDAP): Uniform Resource Locator", RFC
               4516, June 2006.
 [RFC4517]     Legg, S., Ed., "Lightweight Directory Access Protocol
               (LDAP): Syntaxes and Matching Rules", RFC 4517, June
               2006.
 [RFC4520]     Zeilenga, K., "Internet Assigned Numbers Authority
               (IANA) Considerations for the Lightweight Directory
               Access Protocol (LDAP)", BCP 64, RFC 4520, June 2006.
 [Unicode]     The Unicode Consortium, "The Unicode Standard, Version
               3.2.0" is defined by "The Unicode Standard, Version
               3.0" (Reading, MA, Addison-Wesley, 2000. ISBN 0-201-
               61633-5), as amended by the "Unicode Standard Annex
               #27: Unicode 3.1"
               (http://www.unicode.org/reports/tr27/) and by the
               "Unicode Standard Annex #28: Unicode 3.2"
               (http://www.unicode.org/reports/tr28/).
 [X.500]       ITU-T Rec. X.500, "The Directory: Overview of Concepts,
               Models and Service", 1993.
 [X.511]       ITU-T Rec. X.511, "The Directory: Abstract Service
               Definition", 1993.

Sermersheim Standards Track [Page 47] RFC 4511 LDAPv3 June 2006

9. Informative References

 [CharModel]   Whistler, K. and M. Davis, "Unicode Technical Report
               #17, Character Encoding Model", UTR17,
               <http://www.unicode.org/unicode/reports/tr17/>, August
               2000.
 [Glossary]    The Unicode Consortium, "Unicode Glossary",
               <http://www.unicode.org/glossary/>.
 [PortReg]     IANA, "Port Numbers",
               <http://www.iana.org/assignments/port-numbers>.
 [PROTOS-LDAP] University of Oulu, "PROTOS Test-Suite: c06-ldapv3"
               <http://www.ee.oulu.fi/research/ouspg/protos/testing/
               c06/ldapv3/>.

10. IANA Considerations

 The Internet Assigned Numbers Authority (IANA) has updated the LDAP
 result code registry to indicate that this document provides the
 definitive technical specification for result codes 0-36, 48-54, 64-
 70, 80-90.  It is also noted that one resultCode value
 (strongAuthRequired) has been renamed (to strongerAuthRequired).
 The IANA has also updated the LDAP Protocol Mechanism registry to
 indicate that this document and [RFC4513] provides the definitive
 technical specification for the StartTLS (1.3.6.1.4.1.1466.20037)
 Extended operation.
 IANA has assigned LDAP Object Identifier 18 [RFC4520] to identify the
 ASN.1 module defined in this document.
      Subject: Request for LDAP Object Identifier Registration
      Person & email address to contact for further information:
           Jim Sermersheim <jimse@novell.com>
      Specification: RFC 4511
      Author/Change Controller: IESG
      Comments:
           Identifies the LDAP ASN.1 module

Sermersheim Standards Track [Page 48] RFC 4511 LDAPv3 June 2006

Appendix A. LDAP Result Codes

 This normative appendix details additional considerations regarding
 LDAP result codes and provides a brief, general description of each
 LDAP result code enumerated in Section 4.1.9.
 Additional result codes MAY be defined for use with extensions
 [RFC4520].  Client implementations SHALL treat any result code that
 they do not recognize as an unknown error condition.
 The descriptions provided here do not fully account for result code
 substitutions used to prevent unauthorized disclosures (such as
 substitution of noSuchObject for insufficientAccessRights, or
 invalidCredentials for insufficientAccessRights).

A.1. Non-Error Result Codes

 These result codes (called "non-error" result codes) do not indicate
 an error condition:
      success (0),
      compareFalse (5),
      compareTrue (6),
      referral (10), and
      saslBindInProgress (14).
 The success, compareTrue, and compareFalse result codes indicate
 successful completion (and, hence, are referred to as "successful"
 result codes).
 The referral and saslBindInProgress result codes indicate the client
 needs to take additional action to complete the operation.

A.2. Result Codes

 Existing LDAP result codes are described as follows:
    success (0)
       Indicates the successful completion of an operation.  Note:
       this code is not used with the Compare operation.  See
       compareFalse (5) and compareTrue (6).

Sermersheim Standards Track [Page 49] RFC 4511 LDAPv3 June 2006

    operationsError (1)
       Indicates that the operation is not properly sequenced with
       relation to other operations (of same or different type).
       For example, this code is returned if the client attempts to
       StartTLS [RFC4346] while there are other uncompleted operations
       or if a TLS layer was already installed.
    protocolError (2)
       Indicates the server received data that is not well-formed.
       For Bind operation only, this code is also used to indicate
       that the server does not support the requested protocol
       version.
       For Extended operations only, this code is also used to
       indicate that the server does not support (by design or
       configuration) the Extended operation associated with the
       requestName.
       For request operations specifying multiple controls, this may
       be used to indicate that the server cannot ignore the order
       of the controls as specified, or that the combination of the
       specified controls is invalid or unspecified.
    timeLimitExceeded (3)
       Indicates that the time limit specified by the client was
       exceeded before the operation could be completed.
    sizeLimitExceeded (4)
       Indicates that the size limit specified by the client was
       exceeded before the operation could be completed.
    compareFalse (5)
       Indicates that the Compare operation has successfully
       completed and the assertion has evaluated to FALSE or
       Undefined.
    compareTrue (6)
       Indicates that the Compare operation has successfully
       completed and the assertion has evaluated to TRUE.
    authMethodNotSupported (7)
       Indicates that the authentication method or mechanism is not
       supported.

Sermersheim Standards Track [Page 50] RFC 4511 LDAPv3 June 2006

    strongerAuthRequired (8)
       Indicates the server requires strong(er) authentication in
       order to complete the operation.
       When used with the Notice of Disconnection operation, this
       code indicates that the server has detected that an
       established security association between the client and
       server has unexpectedly failed or been compromised.
    referral (10)
       Indicates that a referral needs to be chased to complete the
       operation (see Section 4.1.10).
    adminLimitExceeded (11)
       Indicates that an administrative limit has been exceeded.
    unavailableCriticalExtension (12)
       Indicates a critical control is unrecognized (see Section
       4.1.11).
    confidentialityRequired (13)
       Indicates that data confidentiality protections are required.
    saslBindInProgress (14)
       Indicates the server requires the client to send a new bind
       request, with the same SASL mechanism, to continue the
       authentication process (see Section 4.2).
    noSuchAttribute (16)
       Indicates that the named entry does not contain the specified
       attribute or attribute value.
    undefinedAttributeType (17)
       Indicates that a request field contains an unrecognized
       attribute description.
    inappropriateMatching (18)
       Indicates that an attempt was made (e.g., in an assertion) to
       use a matching rule not defined for the attribute type
       concerned.
    constraintViolation (19)
       Indicates that the client supplied an attribute value that
       does not conform to the constraints placed upon it by the
       data model.
       For example, this code is returned when multiple values are
       supplied to an attribute that has a SINGLE-VALUE constraint.

Sermersheim Standards Track [Page 51] RFC 4511 LDAPv3 June 2006

    attributeOrValueExists (20)
       Indicates that the client supplied an attribute or value to
       be added to an entry, but the attribute or value already
       exists.
    invalidAttributeSyntax (21)
       Indicates that a purported attribute value does not conform
       to the syntax of the attribute.
    noSuchObject (32)
       Indicates that the object does not exist in the DIT.
    aliasProblem (33)
       Indicates that an alias problem has occurred.  For example,
       the code may used to indicate an alias has been dereferenced
       that names no object.
    invalidDNSyntax (34)
       Indicates that an LDAPDN or RelativeLDAPDN field (e.g., search
       base, target entry, ModifyDN newrdn, etc.) of a request does
       not conform to the required syntax or contains attribute
       values that do not conform to the syntax of the attribute's
       type.
    aliasDereferencingProblem (36)
       Indicates that a problem occurred while dereferencing an
       alias.  Typically, an alias was encountered in a situation
       where it was not allowed or where access was denied.
    inappropriateAuthentication (48)
       Indicates the server requires the client that had attempted
       to bind anonymously or without supplying credentials to
       provide some form of credentials.
    invalidCredentials (49)
       Indicates that the provided credentials (e.g., the user's name
       and password) are invalid.
    insufficientAccessRights (50)
       Indicates that the client does not have sufficient access
       rights to perform the operation.
    busy (51)
       Indicates that the server is too busy to service the
       operation.

Sermersheim Standards Track [Page 52] RFC 4511 LDAPv3 June 2006

    unavailable (52)
       Indicates that the server is shutting down or a subsystem
       necessary to complete the operation is offline.
    unwillingToPerform (53)
       Indicates that the server is unwilling to perform the
       operation.
    loopDetect (54)
       Indicates that the server has detected an internal loop (e.g.,
       while dereferencing aliases or chaining an operation).
    namingViolation (64)
       Indicates that the entry's name violates naming restrictions.
    objectClassViolation (65)
       Indicates that the entry violates object class restrictions.
    notAllowedOnNonLeaf (66)
       Indicates that the operation is inappropriately acting upon a
       non-leaf entry.
    notAllowedOnRDN (67)
       Indicates that the operation is inappropriately attempting to
       remove a value that forms the entry's relative distinguished
       name.
    entryAlreadyExists (68)
       Indicates that the request cannot be fulfilled (added, moved,
       or renamed) as the target entry already exists.
    objectClassModsProhibited (69)
       Indicates that an attempt to modify the object class(es) of
       an entry's 'objectClass' attribute is prohibited.
       For example, this code is returned when a client attempts to
       modify the structural object class of an entry.
    affectsMultipleDSAs (71)
       Indicates that the operation cannot be performed as it would
       affect multiple servers (DSAs).
    other (80)
       Indicates the server has encountered an internal error.

Sermersheim Standards Track [Page 53] RFC 4511 LDAPv3 June 2006

Appendix B. Complete ASN.1 Definition

 This appendix is normative.
      Lightweight-Directory-Access-Protocol-V3 {1 3 6 1 1 18}
      -- Copyright (C) The Internet Society (2006).  This version of
      -- this ASN.1 module is part of RFC 4511; see the RFC itself
      -- for full legal notices.
      DEFINITIONS
      IMPLICIT TAGS
      EXTENSIBILITY IMPLIED ::=
      BEGIN
      LDAPMessage ::= SEQUENCE {
           messageID       MessageID,
           protocolOp      CHOICE {
                bindRequest           BindRequest,
                bindResponse          BindResponse,
                unbindRequest         UnbindRequest,
                searchRequest         SearchRequest,
                searchResEntry        SearchResultEntry,
                searchResDone         SearchResultDone,
                searchResRef          SearchResultReference,
                modifyRequest         ModifyRequest,
                modifyResponse        ModifyResponse,
                addRequest            AddRequest,
                addResponse           AddResponse,
                delRequest            DelRequest,
                delResponse           DelResponse,
                modDNRequest          ModifyDNRequest,
                modDNResponse         ModifyDNResponse,
                compareRequest        CompareRequest,
                compareResponse       CompareResponse,
                abandonRequest        AbandonRequest,
                extendedReq           ExtendedRequest,
                extendedResp          ExtendedResponse,
                ...,
                intermediateResponse  IntermediateResponse },
           controls       [0] Controls OPTIONAL }
      MessageID ::= INTEGER (0 ..  maxInt)
      maxInt INTEGER ::= 2147483647 -- (2^^31 - 1) --
      LDAPString ::= OCTET STRING -- UTF-8 encoded,
                                  -- [ISO10646] characters

Sermersheim Standards Track [Page 54] RFC 4511 LDAPv3 June 2006

      LDAPOID ::= OCTET STRING -- Constrained to <numericoid>
                               -- [RFC4512]
      LDAPDN ::= LDAPString -- Constrained to <distinguishedName>
                            -- [RFC4514]
      RelativeLDAPDN ::= LDAPString -- Constrained to <name-component>
                                    -- [RFC4514]
      AttributeDescription ::= LDAPString
                              -- Constrained to <attributedescription>
                              -- [RFC4512]
      AttributeValue ::= OCTET STRING
      AttributeValueAssertion ::= SEQUENCE {
           attributeDesc   AttributeDescription,
           assertionValue  AssertionValue }
      AssertionValue ::= OCTET STRING
      PartialAttribute ::= SEQUENCE {
           type       AttributeDescription,
           vals       SET OF value AttributeValue }
      Attribute ::= PartialAttribute(WITH COMPONENTS {
           ...,
           vals (SIZE(1..MAX))})
      MatchingRuleId ::= LDAPString
      LDAPResult ::= SEQUENCE {
           resultCode         ENUMERATED {
                success                      (0),
                operationsError              (1),
                protocolError                (2),
                timeLimitExceeded            (3),
                sizeLimitExceeded            (4),
                compareFalse                 (5),
                compareTrue                  (6),
                authMethodNotSupported       (7),
                strongerAuthRequired         (8),
                     -- 9 reserved --
                referral                     (10),
                adminLimitExceeded           (11),
                unavailableCriticalExtension (12),
                confidentialityRequired      (13),
                saslBindInProgress           (14),

Sermersheim Standards Track [Page 55] RFC 4511 LDAPv3 June 2006

                noSuchAttribute              (16),
                undefinedAttributeType       (17),
                inappropriateMatching        (18),
                constraintViolation          (19),
                attributeOrValueExists       (20),
                invalidAttributeSyntax       (21),
                     -- 22-31 unused --
                noSuchObject                 (32),
                aliasProblem                 (33),
                invalidDNSyntax              (34),
                     -- 35 reserved for undefined isLeaf --
                aliasDereferencingProblem    (36),
                     -- 37-47 unused --
                inappropriateAuthentication  (48),
                invalidCredentials           (49),
                insufficientAccessRights     (50),
                busy                         (51),
                unavailable                  (52),
                unwillingToPerform           (53),
                loopDetect                   (54),
                     -- 55-63 unused --
                namingViolation              (64),
                objectClassViolation         (65),
                notAllowedOnNonLeaf          (66),
                notAllowedOnRDN              (67),
                entryAlreadyExists           (68),
                objectClassModsProhibited    (69),
                     -- 70 reserved for CLDAP --
                affectsMultipleDSAs          (71),
                     -- 72-79 unused --
                other                        (80),
                ...  },
           matchedDN          LDAPDN,
           diagnosticMessage  LDAPString,
           referral           [3] Referral OPTIONAL }
      Referral ::= SEQUENCE SIZE (1..MAX) OF uri URI
      URI ::= LDAPString     -- limited to characters permitted in
                             -- URIs
      Controls ::= SEQUENCE OF control Control
      Control ::= SEQUENCE {
           controlType             LDAPOID,
           criticality             BOOLEAN DEFAULT FALSE,
           controlValue            OCTET STRING OPTIONAL }

Sermersheim Standards Track [Page 56] RFC 4511 LDAPv3 June 2006

      BindRequest ::= [APPLICATION 0] SEQUENCE {
           version                 INTEGER (1 ..  127),
           name                    LDAPDN,
           authentication          AuthenticationChoice }
      AuthenticationChoice ::= CHOICE {
           simple                  [0] OCTET STRING,
                                   -- 1 and 2 reserved
           sasl                    [3] SaslCredentials,
           ...  }
      SaslCredentials ::= SEQUENCE {
           mechanism               LDAPString,
           credentials             OCTET STRING OPTIONAL }
      BindResponse ::= [APPLICATION 1] SEQUENCE {
           COMPONENTS OF LDAPResult,
           serverSaslCreds    [7] OCTET STRING OPTIONAL }
      UnbindRequest ::= [APPLICATION 2] NULL
      SearchRequest ::= [APPLICATION 3] SEQUENCE {
           baseObject      LDAPDN,
           scope           ENUMERATED {
                baseObject              (0),
                singleLevel             (1),
                wholeSubtree            (2),
                ...  },
           derefAliases    ENUMERATED {
                neverDerefAliases       (0),
                derefInSearching        (1),
                derefFindingBaseObj     (2),
                derefAlways             (3) },
           sizeLimit       INTEGER (0 ..  maxInt),
           timeLimit       INTEGER (0 ..  maxInt),
           typesOnly       BOOLEAN,
           filter          Filter,
           attributes      AttributeSelection }
      AttributeSelection ::= SEQUENCE OF selector LDAPString
                     -- The LDAPString is constrained to
                     -- <attributeSelector> in Section 4.5.1.8
      Filter ::= CHOICE {
           and             [0] SET SIZE (1..MAX) OF filter Filter,
           or              [1] SET SIZE (1..MAX) OF filter Filter,
           not             [2] Filter,
           equalityMatch   [3] AttributeValueAssertion,

Sermersheim Standards Track [Page 57] RFC 4511 LDAPv3 June 2006

           substrings      [4] SubstringFilter,
           greaterOrEqual  [5] AttributeValueAssertion,
           lessOrEqual     [6] AttributeValueAssertion,
           present         [7] AttributeDescription,
           approxMatch     [8] AttributeValueAssertion,
           extensibleMatch [9] MatchingRuleAssertion,
           ...  }
      SubstringFilter ::= SEQUENCE {
           type           AttributeDescription,
           substrings     SEQUENCE SIZE (1..MAX) OF substring CHOICE {
                initial [0] AssertionValue,  -- can occur at most once
                any     [1] AssertionValue,
                final   [2] AssertionValue } -- can occur at most once
           }
      MatchingRuleAssertion ::= SEQUENCE {
           matchingRule    [1] MatchingRuleId OPTIONAL,
           type            [2] AttributeDescription OPTIONAL,
           matchValue      [3] AssertionValue,
           dnAttributes    [4] BOOLEAN DEFAULT FALSE }
      SearchResultEntry ::= [APPLICATION 4] SEQUENCE {
           objectName      LDAPDN,
           attributes      PartialAttributeList }
      PartialAttributeList ::= SEQUENCE OF
                           partialAttribute PartialAttribute
      SearchResultReference ::= [APPLICATION 19] SEQUENCE
                                SIZE (1..MAX) OF uri URI
      SearchResultDone ::= [APPLICATION 5] LDAPResult
      ModifyRequest ::= [APPLICATION 6] SEQUENCE {
           object          LDAPDN,
           changes         SEQUENCE OF change SEQUENCE {
                operation       ENUMERATED {
                     add     (0),
                     delete  (1),
                     replace (2),
                     ...  },
                modification    PartialAttribute } }
      ModifyResponse ::= [APPLICATION 7] LDAPResult

Sermersheim Standards Track [Page 58] RFC 4511 LDAPv3 June 2006

      AddRequest ::= [APPLICATION 8] SEQUENCE {
           entry           LDAPDN,
           attributes      AttributeList }
      AttributeList ::= SEQUENCE OF attribute Attribute
      AddResponse ::= [APPLICATION 9] LDAPResult
      DelRequest ::= [APPLICATION 10] LDAPDN
      DelResponse ::= [APPLICATION 11] LDAPResult
      ModifyDNRequest ::= [APPLICATION 12] SEQUENCE {
           entry           LDAPDN,
           newrdn          RelativeLDAPDN,
           deleteoldrdn    BOOLEAN,
           newSuperior     [0] LDAPDN OPTIONAL }
      ModifyDNResponse ::= [APPLICATION 13] LDAPResult
      CompareRequest ::= [APPLICATION 14] SEQUENCE {
           entry           LDAPDN,
           ava             AttributeValueAssertion }
      CompareResponse ::= [APPLICATION 15] LDAPResult
      AbandonRequest ::= [APPLICATION 16] MessageID
      ExtendedRequest ::= [APPLICATION 23] SEQUENCE {
           requestName      [0] LDAPOID,
           requestValue     [1] OCTET STRING OPTIONAL }
      ExtendedResponse ::= [APPLICATION 24] SEQUENCE {
           COMPONENTS OF LDAPResult,
           responseName     [10] LDAPOID OPTIONAL,
           responseValue    [11] OCTET STRING OPTIONAL }
      IntermediateResponse ::= [APPLICATION 25] SEQUENCE {
           responseName     [0] LDAPOID OPTIONAL,
           responseValue    [1] OCTET STRING OPTIONAL }
      END

Sermersheim Standards Track [Page 59] RFC 4511 LDAPv3 June 2006

Appendix C. Changes

 This appendix is non-normative.
 This appendix summarizes substantive changes made to RFC 2251, RFC
 2830, and RFC 3771.

C.1. Changes Made to RFC 2251

 This section summarizes the substantive changes made to Sections 1,
 2, 3.1, and 4, and the remainder of RFC 2251.  Readers should
 consult [RFC4512] and [RFC4513] for summaries of changes to other
 sections.

C.1.1. Section 1 (Status of this Memo)

  1. Removed IESG note. Post publication of RFC 2251, mandatory LDAP

authentication mechanisms have been standardized which are

   sufficient to remove this note.  See [RFC4513] for authentication
   mechanisms.

C.1.2. Section 3.1 (Protocol Model) and others

  1. Removed notes giving history between LDAP v1, v2, and v3. Instead,

added sufficient language so that this document can stand on its

   own.

C.1.3. Section 4 (Elements of Protocol)

  1. Clarified where the extensibility features of ASN.1 apply to the

protocol. This change affected various ASN.1 types by the

   inclusion of ellipses (...) to certain elements.
 - Removed the requirement that servers that implement version 3 or
   later MUST provide the 'supportedLDAPVersion' attribute.  This
   statement provided no interoperability advantages.

C.1.4. Section 4.1.1 (Message Envelope)

  1. There was a mandatory requirement for the server to return a

Notice of Disconnection and drop the transport connection when a

   PDU is malformed in a certain way.  This has been updated such that
   the server SHOULD return the Notice of Disconnection, and it MUST
   terminate the LDAP Session.

C.1.5. Section 4.1.1.1 (Message ID)

  1. Required that the messageID of requests MUST be non-zero as the

zero is reserved for Notice of Disconnection.

Sermersheim Standards Track [Page 60] RFC 4511 LDAPv3 June 2006

  1. Specified when it is and isn't appropriate to return an already

used messageID. RFC 2251 accidentally imposed synchronous server

   behavior in its wording of this.

C.1.6. Section 4.1.2 (String Types)

  1. Stated that LDAPOID is constrained to <numericoid> from [RFC4512].

C.1.7. Section 4.1.5.1 (Binary Option) and others

  1. Removed the Binary Option from the specification. There are

numerous interoperability problems associated with this method of

   alternate attribute type encoding.  Work to specify a suitable
   replacement is ongoing.

C.1.8. Section 4.1.8 (Attribute)

  1. Combined the definitions of PartialAttribute and Attribute here,

and defined Attribute in terms of PartialAttribute.

C.1.9. Section 4.1.10 (Result Message)

  1. Renamed "errorMessage" to "diagnosticMessage" as it is allowed to

be sent for non-error results.

  1. Moved some language into Appendix A, and referred the reader there.
  2. Allowed matchedDN to be present for other result codes than those

listed in RFC 2251.

  1. Renamed the code "strongAuthRequired" to "strongerAuthRequired" to

clarify that this code may often be returned to indicate that a

   stronger authentication is needed to perform a given operation.

C.1.10. Section 4.1.11 (Referral)

  1. Defined referrals in terms of URIs rather than URLs.
  2. Removed the requirement that all referral URIs MUST be equally

capable of progressing the operation. The statement was ambiguous

   and provided no instructions on how to carry it out.
 - Added the requirement that clients MUST NOT loop between servers.
 - Clarified the instructions for using LDAPURLs in referrals, and in
   doing so added a recommendation that the scope part be present.
 - Removed imperatives which required clients to use URLs in specific
   ways to progress an operation.  These did nothing for
   interoperability.

Sermersheim Standards Track [Page 61] RFC 4511 LDAPv3 June 2006

C.1.11. Section 4.1.12 (Controls)

  1. Specified how control values defined in terms of ASN.1 are to be

encoded.

  1. Noted that the criticality field is only applied to request

messages (except UnbindRequest), and must be ignored when present

   on response messages and UnbindRequest.
 - Specified that non-critical controls may be ignored at the
   server's discretion.  There was confusion in the original wording
   which led some to believe that recognized controls may not be
   ignored as long as they were associated with a proper request.
 - Added language regarding combinations of controls and the ordering
   of controls on a message.
 - Specified that when the semantics of the combination of controls
   is undefined or unknown, it results in a protocolError.
 - Changed "The server MUST be prepared" to "Implementations MUST be
   prepared" in paragraph 8 to reflect that both client and server
   implementations must be able to handle this (as both parse
   controls).

C.1.12. Section 4.2 (Bind Operation)

  1. Mandated that servers return protocolError when the version is not

supported.

  1. Disambiguated behavior when the simple authentication is used, the

name is empty, and the password is non-empty.

  1. Required servers to not dereference aliases for Bind. This was

added for consistency with other operations and to help ensure

   data consistency.
 - Required that textual passwords be transferred as UTF-8 encoded
   Unicode, and added recommendations on string preparation.  This was
   to help ensure interoperability of passwords being sent from
   different clients.

C.1.13. Section 4.2.1 (Sequencing of the Bind Request)

  1. This section was largely reorganized for readability, and language

was added to clarify the authentication state of failed and

   abandoned Bind operations.
 - Removed: "If a SASL transfer encryption or integrity mechanism has
   been negotiated, that mechanism does not support the changing of
   credentials from one identity to another, then the client MUST
   instead establish a new connection."
   If there are dependencies between multiple negotiations of a
   particular SASL mechanism, the technical specification for that
   SASL mechanism details how applications are to deal with them.
   LDAP should not require any special handling.
 - Dropped MUST imperative in paragraph 3 to align with [RFC2119].

Sermersheim Standards Track [Page 62] RFC 4511 LDAPv3 June 2006

  1. Mandated that clients not send non-Bind operations while a Bind is

in progress, and suggested that servers not process them if they

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

C.1.14. Section 4.2.3 (Bind Response)

  1. Moved most error-related text to Appendix A, and added text

regarding certain errors used in conjunction with the Bind

   operation.
 - Prohibited the server from specifying serverSaslCreds when not
   appropriate.

C.1.15. Section 4.3 (Unbind Operation)

  1. Specified that both peers are to cease transmission and terminate

the LDAP session for the Unbind operation.

C.1.16. Section 4.4 (Unsolicited Notification)

  1. Added instructions for future specifications of Unsolicited

Notifications.

C.1.17. Section 4.5.1 (Search Request)

  1. SearchRequest attributes is now defined as an AttributeSelection

type rather than AttributeDescriptionList, and an ABNF is

   provided.
 - SearchRequest attributes may contain duplicate attribute
   descriptions.  This was previously prohibited.  Now servers are
   instructed to ignore subsequent names when they are duplicated.
   This was relaxed in order to allow different short names and also
   OIDs to be requested for an attribute.
 - The present search filter now evaluates to Undefined when the
   specified attribute is not known to the server.  It used to
   evaluate to FALSE, which caused behavior inconsistent with what
   most would expect, especially when the 'not' operator was used.
 - The Filter choice SubstringFilter substrings type is now defined
   with a lower bound of 1.
 - The SubstringFilter substrings 'initial, 'any', and 'final' types
   are now AssertionValue rather than LDAPString.  Also, added
   imperatives stating that 'initial' (if present) must be listed
   first, and 'final' (if present) must be listed last.
 - Disambiguated the semantics of the derefAliases choices.  There was
   question as to whether derefInSearching applied to the base object
   in a wholeSubtree Search.
 - Added instructions for equalityMatch, substrings, greaterOrEqual,
   lessOrEqual, and approxMatch.

Sermersheim Standards Track [Page 63] RFC 4511 LDAPv3 June 2006

C.1.18. Section 4.5.2 (Search Result)

  1. Recommended that servers not use attribute short names when it

knows they are ambiguous or may cause interoperability problems.

  1. Removed all mention of ExtendedResponse due to lack of

implementation.

C.1.19. Section 4.5.3 (Continuation References in the Search Result)

  1. Made changes similar to those made to Section 4.1.11.

C.1.20. Section 4.5.3.1 (Example)

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

C.1.21. Section 4.6 (Modify Operation)

  1. Replaced AttributeTypeAndValues with Attribute as they are

equivalent.

  1. Specified the types of modification changes that might

temporarily violate schema. Some readers were under the impression

   that any temporary schema violation was allowed.

C.1.22. Section 4.7 (Add Operation)

  1. Aligned Add operation with X.511 in that the attributes of the RDN

are used in conjunction with the listed attributes to create the

   entry.  Previously, Add required that the distinguished values be
   present in the listed attributes.
 - Removed requirement that the objectClass attribute MUST be
   specified as some DSE types do not require this attribute.
   Instead, generic wording was added, requiring the added entry to
   adhere to the data model.
 - Removed recommendation regarding placement of objects.  This is
   covered in the data model document.

C.1.23. Section 4.9 (Modify DN Operation)

  1. Required servers to not dereference aliases for Modify DN. This

was added for consistency with other operations and to help ensure

   data consistency.
 - Allow Modify DN to fail when moving between naming contexts.
 - Specified what happens when the attributes of the newrdn are not
   present on the entry.

Sermersheim Standards Track [Page 64] RFC 4511 LDAPv3 June 2006

C.1.24. Section 4.10 (Compare Operation)

  1. Specified that compareFalse means that the Compare took place and

the result is false. There was confusion that led people to

   believe that an Undefined match resulted in compareFalse.
 - Required servers to not dereference aliases for Compare.  This was
   added for consistency with other operations and to help ensure
   data consistency.

C.1.25. Section 4.11 (Abandon Operation)

  1. Explained that since Abandon returns no response, clients should

not use it if they need to know the outcome.

  1. Specified that Abandon and Unbind cannot be abandoned.

C.1.26. Section 4.12 (Extended Operation)

  1. Specified how values of Extended operations defined in terms of

ASN.1 are to be encoded.

  1. Added instructions on what Extended operation specifications

consist of.

  1. Added a recommendation that servers advertise supported Extended

operations.

C.1.27. Section 5.2 (Transfer Protocols)

  1. Moved referral-specific instructions into referral-related

sections.

C.1.28. Section 7 (Security Considerations)

  1. Reworded notes regarding SASL not protecting certain aspects of

the LDAP Bind messages.

  1. Noted that Servers are encouraged to prevent directory

modifications by clients that have authenticated anonymously

   [RFC4513].
 - Added a note regarding the possibility of changes to security
   factors (authentication, authorization, and data confidentiality).
 - Warned against following referrals that may have been injected in
   the data stream.
 - Noted that servers should protect information equally, whether in
   an error condition or not, and mentioned matchedDN,
   diagnosticMessage, and resultCodes specifically.
 - Added a note regarding malformed and long encodings.

Sermersheim Standards Track [Page 65] RFC 4511 LDAPv3 June 2006

C.1.29. Appendix A (Complete ASN.1 Definition)

  1. Added "EXTENSIBILITY IMPLIED" to ASN.1 definition.
  2. Removed AttributeType. It is not used.

C.2. Changes Made to RFC 2830

 This section summarizes the substantive changes made to Sections of
 RFC 2830.  Readers should consult [RFC4513] for summaries of changes
 to other sections.

C.2.1. Section 2.3 (Response other than "success")

  1. Removed wording indicating that referrals can be returned from

StartTLS.

  1. Removed requirement that only a narrow set of result codes can be

returned. Some result codes are required in certain scenarios, but

   any other may be returned if appropriate.
 - Removed requirement that the ExtendedResponse.responseName MUST be
   present.  There are circumstances where this is impossible, and
   requiring this is at odds with language in Section 4.12.

C.2.1. Section 4 (Closing a TLS Connection)

  1. Reworded most of this section to align with definitions of the

LDAP protocol layers.

  1. Removed instructions on abrupt closure as this is covered in other

areas of the document (specifically, Section 5.3)

C.3. Changes Made to RFC 3771

  1. Rewrote to fit into this document. In general, semantics were

preserved. Supporting and background language seen as redundant

   due to its presence in this document was omitted.
  1. Specified that Intermediate responses to a request may be of

different types, and one of the response types may be specified to

   have no response value.

Sermersheim Standards Track [Page 66] RFC 4511 LDAPv3 June 2006

Editor's Address

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

Sermersheim Standards Track [Page 67] RFC 4511 LDAPv3 June 2006

Full Copyright Statement

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 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
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Sermersheim Standards Track [Page 68]

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