Internet-Draft                                  Editor:  J. Sermersheim 
Intended Category: Standard Track                           Novell, Inc 
Document: draft-ietf-ldapbis-protocol-27.txt                   Oct 2004 
Obsoletes: RFCs 2251, 2830, 3771                                        
 
    
                            LDAP: The Protocol 
 
 
Status of this Memo 
 
   This document is an Internet-Draft and is subject to all provisions 
   of section 3 of RFC 3667. By submitting this Internet-Draft, each 
   author represents that any applicable patent or other IPR claims of 
   which he or she is aware have been or will be disclosed, and any of 
   which he or she become aware will be disclosed, in accordance with 
   RFC 3668. 
    
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   This Internet-Draft will expire in February 2005.  
    
   Technical discussion of this document will take place on the IETF 
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   ldapbis@openldap.org>. Please send editorial comments directly to the 
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Copyright Notice 
    
   Copyright (C) The Internet Society 2004. All Rights Reserved. 
 
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). 
    
 
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Table of Contents 
    
   1. Introduction....................................................3 
   1.1. Relationship to Obsolete Specifications.......................3 
   2. Conventions.....................................................3 
   3. Protocol Model..................................................4 
   3.1 Operation and LDAP Exchange Relationship.......................4 
   4. Elements of Protocol............................................5 
   4.1. Common Elements...............................................5 
   4.1.1. Message Envelope............................................5 
   4.1.2. String Types................................................7 
   4.1.3. Distinguished Name and Relative Distinguished Name..........7 
   4.1.4. Attribute Descriptions......................................7 
   4.1.5. Attribute Value.............................................8 
   4.1.6. Attribute Value Assertion...................................8 
   4.1.7. Attribute and PartialAttribute..............................9 
   4.1.8. Matching Rule Identifier....................................9 
   4.1.9. Result Message..............................................9 
   4.1.10. Referral..................................................11 
   4.1.11. Controls..................................................12 
   4.2. Bind Operation...............................................14 
   4.3. Unbind Operation.............................................17 
   4.4. Unsolicited Notification.....................................17 
   4.5. Search Operation.............................................18 
   4.6. Modify Operation.............................................27 
   4.7. Add Operation................................................28 
   4.8. Delete Operation.............................................29 
   4.9. Modify DN Operation..........................................30 
   4.10. Compare Operation...........................................31 
   4.11. Abandon Operation...........................................32 
   4.12. Extended Operation..........................................32 
   4.13. IntermediateResponse Message................................34 
   4.13.1. Usage with LDAP ExtendedRequest and ExtendedResponse......34 
   4.13.2. Usage with LDAP Request Controls..........................35 
   4.14. StartTLS Operation..........................................35 
   5. Protocol Encoding, Connection, and Transfer....................37 
   5.2. Protocol Encoding............................................37 
   5.3. Transmission Control Protocol (TCP)..........................38 
   6. Security Considerations........................................38 
   7. Acknowledgements...............................................39 
   8. Normative References...........................................40 
   9. Informative References.........................................41 
   10. IANA Considerations...........................................42 
   11. Editor's Address..............................................42 
   Appendix A - LDAP Result Codes....................................43 
   A.1 Non-Error Result Codes........................................43 
   A.2 Result Codes..................................................43 
   Appendix B - Complete ASN.1 Definition............................48 
   Appendix C - Changes..............................................54 
   C.1 Changes made to RFC 2251:.....................................54 
   C.2 Changes made to RFC 2830:.....................................59 
   C.3 Changes made to RFC 3771:.....................................59 
    
  
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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 Obsolete Specifications 
    
   This document is an integral part of the LDAP Technical Specification 
   [Roadmap] which obsoletes the previously defined LDAP technical 
   specification, RFC 3377, in its entirety. 
    
   This document obsoletes all of RFC 2251 except the following: 
   Sections 3.2, 3.4, 4.1.3 (last paragraph), 4.1.4, 4.1.5, 4.1.5.1, 
   4.1.9 (last paragraph), 5.1, 6.1, and 6.2 (last paragraph) are 
   obsoleted by [Models]. 
   Section 3.3 is obsoleted by [Roadmap]. 
   Sections 4.2.1 (portions), and 4.2.2 are obsoleted by [AuthMeth]. 
    
   Appendix C.1 summarizes substantive changes to the remaining 
   sections. 
    
   This document obsoletes RFC 2830, Sections 2 and 4 in entirety. The 
   remainder of RFC 2830 is obsoleted by [AuthMeth]. Appendix C.2 
   summarizes substantive changes to the remaining sections. 
    
   This document also obsoletes RFC 3771 in entirety. 
    
    
2. Conventions 
    
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
   "SHOULD", "SHOULD NOT", "RECOMMENDED", and "MAY" in this document are 
   to be interpreted as described in [Keyword]. 
    
   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>. 
    
   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]. 
    
  
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   The term "connection" refers to the underlying transport service used 
   to carry the protocol exchange. 
    
   The term "LDAP exchange" refers to the layer where LDAP PDUs are 
   exchanged between protocol peers. 
    
   The term "TLS layer" refers to a layer inserted between the 
   connection and the LDAP exchange that utilizes Transport Layer 
   Security ([TLS]) to protect the exchange of LDAP PDUs. 
    
   The term "SASL layer" refers to a layer inserted between the 
   connection and the LDAP exchange that utilizes Simple Authentication 
   and Security Layer ([SASL]) to protect the exchange of LDAP PDUs. 
    
   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. 
 
   The core protocol operations defined in this document can be mapped 
   to a subset of the X.500 (1993) Directory Abstract Service [X.511]. 
   However there is not a one-to-one mapping between LDAP operations and 
   X.500 Directory Access Protocol (DAP) operations. Server 
   implementations acting as a gateway to X.500 directories may need to 
   make multiple DAP requests to service a single LDAP request. 
 
 
3.1 Operation and LDAP Exchange Relationship 
    
   Protocol operations are tied to an LDAP exchange. When the connection 
   is closed, any uncompleted operations tied to the LDAP exchange are, 
   when possible, abandoned, and when not possible, completed without 
   transmission of the response. Also, when the connection is closed, 
   the client MUST NOT assume that any uncompleted update operations 
   tied to the LDAP exchange have succeeded or failed. 
  
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4. Elements of Protocol 
    
   The protocol is described using Abstract Syntax Notation One 
   ([ASN.1]), and is transferred using a subset of ASN.1 Basic Encoding 
   Rules ([BER]). Section 5 specifies how the protocol elements are 
   encoded and transferred. 
 
   In order to support future extensions to this protocol, extensibility 
   is implied where it is allowed per ASN.1 (i.e. sequence, set, choice, 
   and enumerated types are extensible). In addition, ellipses (...) 
   have been supplied in ASN.1 types that are explicitly extensible as 
   discussed in [LDAPIANA]. Because of the implied extensibility, 
   clients and servers MUST (unless otherwise specified) ignore trailing 
   SEQUENCE components whose tags they do not recognize.  
    
   Changes to the protocol other than through the extension mechanisms 
   described here require a different version number. A client indicates 
   the version it is using as part of the bind request, described in 
   Section 4.2. If a client has not sent a bind, the server MUST assume 
   the client is using version 3 or later. 
    
   Clients may determine the protocol versions a server supports by 
   reading the 'supportedLDAPVersion' attribute from the root DSE (DSA-
   Specific Entry) [Models]. 
    
    
4.1. Common Elements 
    
   This section describes the LDAPMessage envelope Protocol Data Unit 
   (PDU) format, as well as data type definitions, which are used in the 
   protocol operations. 
    
    
4.1.1. Message Envelope 
    
   For the purposes of protocol exchanges, all protocol operations are 
   encapsulated in a common envelope, the LDAPMessage, which is defined 
   as follows: 
    
        LDAPMessage ::= SEQUENCE { 
             messageID       MessageID, 
             protocolOp      CHOICE { 
                  bindRequest           BindRequest, 
                  bindResponse          BindResponse, 
                  unbindRequest         UnbindRequest, 
                  searchRequest         SearchRequest, 
                  searchResEntry        SearchResultEntry, 
                  searchResDone         SearchResultDone, 
                  searchResRef          SearchResultReference, 
                  modifyRequest         ModifyRequest, 
                  modifyResponse        ModifyResponse, 
                  addRequest            AddRequest, 
  
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                  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 a PDU from the client in which the LDAPMessage 
   SEQUENCE tag cannot be recognized, the messageID cannot be parsed, 
   the tag of the protocolOp is not recognized as a request, or the 
   encoding structures or lengths of data fields are found to be 
   incorrect, then the server SHOULD return the Notice of Disconnection 
   described in Section 4.4.1, with the resultCode set to protocolError, 
   and MUST immediately close the connection.  
    
   In other cases where the client or server cannot parse a PDU, it 
   SHOULD abruptly close the connection where further communication 
   (including providing notice) would be pernicious. Otherwise, server 
   implementations MUST return an appropriate response to the request, 
   with the resultCode set to protocolError. 
    
    
4.1.1.1. Message ID 
    
   All LDAPMessage envelopes encapsulating responses contain the 
   messageID value of the corresponding request LDAPMessage. 
    
   The message ID of a request MUST have a non-zero value different from 
   the the messageID of any other uncompleted requests in the LDAP 
   exchange. The zero value is reserved for the unsolicited notification 
   message. 
    
   Typical clients increment a counter for each request. 
    
   A client MUST NOT send a request with the same message ID as an 
   earlier request in the same LDAP exchange unless it can be determined 
   that the server is no longer servicing the earlier request (e.g. 
  
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   after the final response is received, or a subsequent bind 
   completes). Otherwise the behavior is undefined. For this purpose, 
   note that abandon and abandoned operations do not send responses. 
 
 
4.1.2. String Types 
    
   The LDAPString is a notational convenience to indicate that, although 
   strings of LDAPString type encode as ASN.1 OCTET STRING types, the 
   [ISO10646] character set (a superset of [Unicode]) is used, encoded 
   following the [UTF-8] algorithm. Note that Unicode characters U+0000 
   through U+007F are the same as ASCII 0 through 127, respectively, and 
   have the same single octet UTF-8 encoding.  Other Unicode characters 
   have a multiple octet UTF-8 encoding. 
    
        LDAPString ::= OCTET STRING -- UTF-8 encoded, 
                                    -- [ISO10646] characters 
    
   The LDAPOID is a notational convenience to indicate that the 
   permitted value of this string is a (UTF-8 encoded) dotted-decimal 
   representation of an OBJECT IDENTIFIER. Although an LDAPOID is 
   encoded as an OCTET STRING, values are limited to the definition of 
   <numericoid> given in Section 1.4 of [Models]. 
    
        LDAPOID ::= OCTET STRING -- Constrained to <numericoid> [Models] 
         
   For example, 
    
        1.3.6.1.4.1.1466.1.2.3 
    
    
4.1.3. Distinguished Name and Relative Distinguished Name 
    
   An LDAPDN is defined to be the representation of a Distinguished Name 
   (DN) after encoding according to the specification in [LDAPDN]. 
    
        LDAPDN ::= LDAPString 
                   -- Constrained to <distinguishedName> [LDAPDN] 
    
   A RelativeLDAPDN is defined to be the representation of a Relative 
   Distinguished Name (RDN) after encoding according to the 
   specification in [LDAPDN]. 
    
        RelativeLDAPDN ::= LDAPString 
                           -- Constrained to <name-component> [LDAPDN] 
    
    
4.1.4. Attribute Descriptions 
    
   The definition and encoding rules for attribute descriptions are 
   defined in Section 2.5 of [Models]. Briefly, an attribute description 
   is an attribute type and zero or more options. 
    
        AttributeDescription ::= LDAPString 
  
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                                -- Constrained to <attributedescription> 
                                -- [Models] 
         
 
4.1.5. Attribute Value 
    
   A field of type AttributeValue is an OCTET STRING containing an 
   encoded attribute value. The attribute value is encoded according to 
   the LDAP-specific encoding definition of its corresponding syntax. 
   The LDAP-specific encoding definitions for different syntaxes and 
   attribute types may be found in other documents and in particular 
   [Syntaxes]. 
 
        AttributeValue ::= OCTET STRING 
    
   Note that there is no defined limit on the size of this encoding; 
   thus protocol values may include multi-megabyte attribute values 
   (e.g. photographs). 
    
   Attribute values may be defined which have arbitrary and non-
   printable syntax. Implementations MUST NOT display nor attempt to 
   decode an attribute value if its syntax is not known. The 
   implementation may attempt to discover the subschema of the source 
   entry, and retrieve the descriptions of 'attributeTypes' from it 
   [Models]. 
    
   Clients MUST only send attribute values in a request that are valid 
   according to the syntax defined for the attributes. 
    
    
4.1.6. Attribute Value Assertion 
    
   The AttributeValueAssertion (AVA) type definition is similar to the 
   one in the X.500 Directory standards. It contains an attribute 
   description and a matching rule ([Models Section 4.1.3) assertion 
   value suitable for that type. Elements of this type are typically 
   used to assert that the value in assertionValue matches a value of an 
   attribute. 
    
        AttributeValueAssertion ::= SEQUENCE { 
             attributeDesc   AttributeDescription, 
             assertionValue  AssertionValue } 
    
        AssertionValue ::= OCTET STRING 
    
   The syntax of the AssertionValue depends on the context of the LDAP 
   operation being performed. For example, the syntax of the EQUALITY 
   matching rule for an attribute is used when performing a Compare 
   operation. Often this is the same syntax used for values of the 
   attribute type, but in some cases the assertion syntax differs from 
   the value syntax. See objectIdentiferFirstComponentMatch in 
   [Syntaxes] for an example. 
    
    
  
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4.1.7. Attribute and PartialAttribute 
    
   Attributes and partial attributes consist of an attribute description 
   and attribute values. A PartialAttribute allows zero values, while 
   Attribute requires at least one value. 
    
        PartialAttribute ::= SEQUENCE { 
             type       AttributeDescription, 
             vals       SET OF value AttributeValue } 
    
        Attribute ::= PartialAttribute(WITH COMPONENTS { 
             ...,  
             vals (SIZE(1..MAX))}) 
    
   No two attribute values may be equivalent as described by Section 2.3 
   of [Models]. The set of attribute values is unordered. 
   Implementations MUST NOT rely upon the ordering being repeatable. 
    
    
4.1.8. Matching Rule Identifier 
    
   Matching rules are defined in Section 4.1.3 of [Models]. A matching 
   rule is identified in the protocol by the printable representation of 
   either its <numericoid>, or one of its short name descriptors 
   [Models], e.g. 'caseIgnoreMatch' or '2.5.13.2'. 
    
        MatchingRuleId ::= LDAPString 
         
    
4.1.9. Result Message 
    
   The LDAPResult is the construct used in this protocol to return 
   success or failure indications from servers to clients. To various 
   requests, servers will return responses of LDAPResult or responses 
   containing the components of LDAPResult to indicate the final status 
   of a protocol operation request. 
    
        LDAPResult ::= SEQUENCE { 
             resultCode         ENUMERATED { 
                  success                      (0), 
                  operationsError              (1), 
                  protocolError                (2), 
                  timeLimitExceeded            (3), 
                  sizeLimitExceeded            (4), 
                  compareFalse                 (5), 
                  compareTrue                  (6), 
                  authMethodNotSupported       (7), 
                  strongAuthRequired           (8), 
                       -- 9 reserved -- 
                  referral                     (10), 
                  adminLimitExceeded           (11), 
                  unavailableCriticalExtension (12), 
                  confidentialityRequired      (13), 
                  saslBindInProgress           (14), 
  
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                  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 } 
    
   The resultCode enumeration is extensible as defined in Section 3.6 of 
   [LDAPIANA]. The meanings of the listed result codes are given in 
   Appendix A. If a server detects multiple errors for an operation, 
   only one result code is returned. The server should return the result 
   code that best indicates the nature of the error encountered. 
    
   The diagnosticMessage field of this construct may, at the server's 
   option, be used to return a string containing a textual, human-
   readable (terminal control and page formatting characters should be 
   avoided) diagnostic message. As this diagnostic message is not 
   standardized, implementations MUST NOT rely on the values returned. 
   If the server chooses not to return a textual diagnostic, the 
   diagnosticMessage field MUST be empty. 
    
   For certain result codes (typically, but not restricted to 
   noSuchObject, aliasProblem, invalidDNSyntax and 
   aliasDereferencingProblem), the matchedDN field is set (subject to 
   access controls) to the name of the last entry (object or alias) used 
  
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   in finding the target (or base) object. If no aliases were 
   dereferenced while attempting to locate the entry, this will be a 
   truncated form of the name provided or if aliases were dereferenced, 
   of the resulting name, as defined in Section 12.5 of [X.511]. 
   Otherwise the matchedDN field is empty. 
    
    
4.1.10. Referral 
    
   The referral result code indicates that the contacted server cannot 
   or will not perform the operation and that one or more other servers 
   may be able to. Reasons for this include: 
    
   - The target entry of the request is not held locally, but the 
     server has knowledge of its possible existence elsewhere. 
    
   - The operation is restricted on this server -- perhaps due to a 
     read-only copy of an entry to be modified. 
    
   The referral field is present in an LDAPResult if the resultCode 
   field value is referral, and absent with all other result codes. It 
   contains one or more references to one or more servers or services 
   that may be accessed via LDAP or other protocols. Referrals can be 
   returned in response to any operation request (except unbind and 
   abandon which do not have responses). At least one URI MUST be 
   present in the Referral. 
    
   During a search operation, after the baseObject is located, and 
   entries are being evaluated, the referral is not returned. Instead, 
   continuation references, described in Section 4.5.3, are returned 
   when other servers would need to be contacted to complete the 
   operation. 
    
        Referral ::= SEQUENCE SIZE (1..MAX) OF uri URI 
    
        URI ::= LDAPString     -- limited to characters permitted in 
                               -- URIs 
    
   If the client wishes to progress the operation, it MUST follow the 
   referral by contacting one of the supported services. If multiple 
   URIs are present, the client assumes that any supported URI may be 
   used to progress the operation. 
    
   Protocol peers that follow referrals MUST ensure that they do not 
   loop between servers. They MUST NOT repeatedly contact the same 
   server for the same request with the same target entry name, scope 
   and filter. Some implementations use a counter that is incremented 
   each time referral handling occurs for an operation, and these kinds 
   of implementations MUST be able to handle at least ten nested 
   referrals between the root and a leaf entry. 
    
   A URI for a server implementing LDAP and accessible via [TCP]/[IP] 
   (v4 or v6) is written as an LDAP URL according to [LDAPURL].  
    
  
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   When an LDAP URL is used, the following instructions are followed: 
    
   - If an alias was dereferenced, the <dn> part of the URL MUST be 
     present, with the new target object name. UTF-8 encoded characters 
     appearing in the string representation of a DN or search filter 
     may not be legal for URLs (e.g. spaces) and MUST be escaped using 
     the % method in [URI]. 
    
   - It is RECOMMENDED that the <dn> part be present to avoid 
     ambiguity. 
    
   - If the <dn> part is present, the client MUST use this name in its 
     next request to progress the operation, and if it is not present 
     the client will use the same name as in the original request.  
    
   - Some servers (e.g. participating in distributed indexing) may 
     provide a different filter in a URL of a referral for a search 
     operation. 
    
   - If the <filter> part of the LDAP URL is present, the client MUST 
     use this filter in its next request to progress this search, and 
     if it is not present the client MUST use the same filter as it 
     used for that search. 
    
   - For search, it is RECOMMENDED that the <scope> part be present to 
     avoid ambiguity. 
    
   - If the <scope> part is missing, the scope of the original search 
     is used by the client to progress the operation. 
    
   - Other aspects of the new request may be the same as or different 
     from the request which generated the referral. 
    
   Other kinds of URIs may be returned. The syntax and semantics of such 
   URIs is left to future specifications. Clients may ignore URIs that 
   they do not support. 
    
    
4.1.11. Controls 
    
   Controls provide a mechanism whereby the semantics and arguments of 
   existing LDAP operations may be extended. One or more controls may be 
   attached to a single LDAP message. A control only affects the 
   semantics of the message it is attached to. 
    
   Controls sent by clients are termed 'request controls' and those sent 
   by servers are termed 'response controls'. 
    
        Controls ::= SEQUENCE OF control Control 
    
        Control ::= SEQUENCE { 
             controlType             LDAPOID, 
             criticality             BOOLEAN DEFAULT FALSE, 
             controlValue            OCTET STRING OPTIONAL } 
  
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   The controlType field is the dotted-decimal representation of an 
   OBJECT IDENTIFIER which uniquely identifies the control. This 
   provides unambiguous naming of controls. Often, response control(s) 
   solicited by a request control share controlType values with the 
   request control. 
    
   The criticality field only has meaning in controls attached to 
   request messages (except unbindRequest). For controls attached to 
   response messages and the unbindRequest, the criticality field SHOULD 
   be FALSE, and MUST be ignored by the receiving protocol peer. A value 
   of TRUE indicates that it is unacceptable to perform the operation 
   without applying the semantics of the control and FALSE otherwise. 
   Specifically, the criticality field is applied as follows: 
    
   - Regardless of the value of the criticality field, if the server 
     recognizes the control type and it is appropriate for the 
     operation, the server is to make use of the control when 
     performing the operation. 
    
   - If the server does not recognize the control type or it is not 
     appropriate for the operation, and the criticality field is TRUE, 
     the server MUST NOT perform the operation, and for operations that 
     have a response message, MUST return unavailableCriticalExtension 
     in the resultCode. 
    
   - If the server does not recognize the control type or it is not 
     appropriate for the operation, and the criticality field is FALSE, 
     the server MUST ignore the control. 
    
   The controlValue may contain information associated with the 
   controlType. Its format is defined by the specification of the 
   control. Implementations MUST be prepared to handle arbitrary 
   contents of the controlValue octet string, including zero bytes. It 
   is absent only if there is no value information which is associated 
   with a control of its type. When a controlValue is defined in terms 
   of ASN.1, and BER encoded according to Section 5.2, it also follows 
   the extensibility rules in Section 4. 
 
   Servers list the controlType of request controls they recognize in 
   the 'supportedControl' attribute in the root DSE (Section 5.1 of 
   [Models]). 
 
   Controls SHOULD NOT be combined unless the semantics of the 
   combination has been specified. The semantics of control 
   combinations, if specified, are generally found in the control 
   specification most recently published. When a combination of controls 
   is encountered whose semantics are invalid, not specified (or not 
   known), the message is considered to be not well-formed, thus the 
   operation fails with protocolError. Additionally, unless order-
   dependent semantics are given in a specification, the order of a 
   combination of controls in the SEQUENCE is ignored. Where the order 
   is to be ignored but cannot be ignored by the server, the message is 


  
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   considered not well-formed and the operation fails with 
   protocolError. 
    
   This document does not specify any controls. Controls may be 
   specified in other documents. Documents detailing control extensions 
   are to provide for each control: 
    
   - the OBJECT IDENTIFIER assigned to the control, 
    
   - direction as to what value the sender should provide for the 
     criticality field (note: the semantics of the criticality field 
     are defined above should not be altered by the control's 
     specification),  
    
   - whether information is to be present in the controlValue field, 
     and if so, the format of the controlValue contents, 
    
   - the semantics of the control, and 
    
   - optionally, semantics regarding the combination of the control 
     with other controls. 
    
    
4.2. Bind Operation 
    
   The function of the Bind Operation is to allow authentication 
   information to be exchanged between the client and server. The Bind 
   operation should be thought of as the "authenticate" operation. 
   Operational, authentication, and security-related semantics of this 
   operation are given in [AuthMeth].  
    
   The Bind Request is defined as follows: 
    
        BindRequest ::= [APPLICATION 0] SEQUENCE { 
             version                 INTEGER (1 .. 127), 
             name                    LDAPDN, 
             authentication          AuthenticationChoice } 
    
        AuthenticationChoice ::= CHOICE { 
             simple                  [0] OCTET STRING, 
                                     -- 1 and 2 reserved 
             sasl                    [3] SaslCredentials, 
             ... } 
    
        SaslCredentials ::= SEQUENCE { 
             mechanism               LDAPString, 
             credentials             OCTET STRING OPTIONAL } 
    
   Fields of the Bind Request are: 
    
   - version: A version number indicating the version of the protocol 
     to be used for the LDAP exchange. 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 
  
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     support the specified version, it MUST respond with protocolError 
     in the resultCode field of the BindResponse. 
    
   - 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 
     ([AuthMeth] Section 5.1) or when using Simple Authentication and 
     Security Layer [SASL] authentication ([AuthMeth] Section 3.3.2). 
     Where the server attempts to locate the named object, it SHALL NOT 
     perform alias dereferencing. 
    
   - authentication: information used in authentication. This type is 
     extensible as defined in Section 3.7 of [LDAPIANA]. Servers that 
     do not support a choice supplied by a client return 
     authMethodNotSupported in the resultCode field of the 
     BindResponse. 
      
     Textual passwords (consisting of a character sequence with a known 
     character set and encoding) transferred to the server using the 
     simple AuthenticationChoice SHALL be transferred as [UTF-8] 
     encoded [Unicode]. Prior to transfer, clients SHOULD prepare text 
     passwords by applying the [SASLprep] profile of the [Stringprep] 
     algorithm. Passwords consisting of other data (such as random 
     octets) MUST NOT be altered. The determination of whether a 
     password is textual is a local client matter. 
    
   Authorization is the decision of which access an operation has to the 
   directory. Among other things, the process of authorization takes as 
   input authentication information obtained during the bind operation 
   and/or other acts of authentication (such as lower layer security 
   services). 
    
    
4.2.1. Processing of the Bind Request 
    
   Before processing a BindRequest, all uncompleted operations MUST 
   either complete or be abandoned. The server may either wait for the 
   uncompleted operations to complete, or abandon them. The server then 
   proceeds to authenticate the client in either a single-step, or 
   multi-step bind process. Each step requires the server to return a 
   BindResponse to indicate the status of authentication.  
    
   After sending a BindRequest, clients MUST NOT send further LDAP PDUs 
   until receiving the BindResponse. Similarly, servers SHOULD NOT 
   process or respond to requests received while processing a 
   BindRequest. 
 
   If the client did not bind before sending a request and receives an 
   operationsError to that request, it may then send a Bind Request. If 
   this also fails or the client chooses not to bind on the existing 
   LDAP exchange, it may close the connection, reopen it and begin again 
   by first sending a PDU with a Bind Request. This will aid in 
   interoperating with servers implementing other versions of LDAP. 
    
  
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   Clients may send multiple Bind Requests on an LDAP exchange to change 
   the authentication and/or security associations or to complete a 
   multi-stage bind process. Authentication from earlier binds is 
   subsequently ignored. 
 
   For some SASL authentication mechanisms, it may be necessary for the 
   client to invoke the BindRequest multiple times ([AuthMeth] Section 
   8.2). Clients MUST NOT invoke operations between two Bind Requests 
   made as part of a multi-stage bind. 
    
   A client may abort a SASL bind negotiation by sending a BindRequest 
   with a different value in the mechanism field of SaslCredentials, or 
   an AuthenticationChoice other than sasl. 
    
   If the client sends a BindRequest with the sasl mechanism field as an 
   empty string, the server MUST return a BindResponse with 
   authMethodNotSupported as the resultCode. This will allow clients to 
   abort a negotiation if it wishes to try again with the same SASL 
   mechanism. 
    
    
4.2.2. Bind Response 
    
   The Bind Response is defined as follows. 
    
        BindResponse ::= [APPLICATION 1] SEQUENCE { 
             COMPONENTS OF LDAPResult, 
             serverSaslCreds    [7] OCTET STRING OPTIONAL } 
    
   BindResponse consists simply of an indication from the server of the 
   status of the client's request for authentication. 
    
   A successful bind operation is indicated by a BindResponse with a 
   resultCode set to success. Otherwise, an appropriate result code is 
   set in the BindResponse. For bind, the protocolError result code may 
   be used to indicate that the version number supplied by the client is 
   unsupported. 
 
   If the client receives a BindResponse where the resultCode field is 
   protocolError, it is to assume that the server does not support this 
   version of LDAP. While the client may be able proceed with another 
   version of this protocol (this may or may not require closing and re-
   establishing the connection), how to proceed with another version of 
   this protocol is beyond the scope of this document. Clients which are 
   unable or unwilling to proceed SHOULD close the connection. 
    
   The serverSaslCreds field is used as part of a SASL-defined bind 
   mechanism to allow the client to authenticate the server to which it 
   is communicating, or to perform "challenge-response" authentication. 
   If the client bound with the simple choice, or the SASL mechanism 
   does not require the server to return information to the client, then 
   this field SHALL NOT be included in the BindResponse. 
    
    
  
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4.3. Unbind Operation 
    
   The function of the Unbind Operation is to terminate an LDAP exchange 
   and close the connection. The Unbind operation is not the antithesis 
   of the Bind operation as the name implies. The naming of these 
   operations is historical. The Unbind operation should be thought of 
   as the "quit" operation. 
    
   The Unbind Operation is defined as follows: 
    
        UnbindRequest ::= [APPLICATION 2] NULL 
    
   The Unbind Operation has no response defined. Upon transmission of 
   the UnbindRequest, each protocol peer is to consider the LDAP 
   exchange terminated, MUST cease transmission of messages to the other 
   peer, and MUST close the connection. Uncompleted operations are 
   handled as specified in Section 5.1. 
    
    
4.4. Unsolicited Notification 
    
   An unsolicited notification is an LDAPMessage sent from the server to 
   the client which is not in response to any LDAPMessage received by 
   the server. It is used to signal an extraordinary condition in the 
   server or in the LDAP exchange or connection between the client and 
   the server. The notification is of an advisory nature, and the server 
   will not expect any response to be returned from the client. 
    
   The unsolicited notification is structured as an LDAPMessage in which 
   the messageID is zero and protocolOp is of the extendedResp form (See 
   Section 4.12). The responseName field of the ExtendedResponse always 
   contains an LDAPOID which is unique for this notification. 
    
   One unsolicited notification (Notice of Disconnection) is defined in 
   this document. The specification of an unsolicited notification 
   consists of: 
    
   - the OBJECT IDENTIFIER assigned to the notification (to be 
     specified in the responseName, 
    
   - the format of the contents (if any) of the responseValue, 
    
   - the circumstances which will cause the notification to be 
     returned, and 
    
   - the semantics of the operation. 
    
    
4.4.1. Notice of Disconnection 
    
   This notification may be used by the server to advise the client that 
   the server is about to close the connection due to an error 
   condition. This notification is intended to assist clients in 
   distinguishing between an error condition and a transient network 
  
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   failure. Note that this notification is not a response to an unbind 
   requested by the client. Uncompleted operations are handled as 
   specified in Section 5.1. 
    
   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. 
    
   Upon transmission of the Notice of Disconnection, the server is to 
   consider the LDAP exchange terminated, MUST cease transmission of 
   messages to the client, and MUST close the connection. 
    
    
4.5. Search Operation 
    
   The Search Operation is used to request a server to return, subject 
   to access controls and other restrictions, a set of entries matching 
   a complex search criterion. This can be used to read attributes from 
   a single entry, from entries immediately subordinate to a particular 
   entry, or a whole subtree of entries. 
    
    
4.5.1. Search Request 
    
   The Search Request is defined as follows: 
    
        SearchRequest ::= [APPLICATION 3] SEQUENCE { 
             baseObject      LDAPDN, 
             scope           ENUMERATED { 
                  baseObject              (0), 
                  singleLevel             (1), 
                  wholeSubtree            (2) }, 
             derefAliases    ENUMERATED { 
                  neverDerefAliases       (0), 
                  derefInSearching        (1), 
                  derefFindingBaseObj     (2), 
                  derefAlways             (3) }, 
             sizeLimit       INTEGER (0 .. maxInt), 
             timeLimit       INTEGER (0 .. maxInt), 
             typesOnly       BOOLEAN, 
             filter          Filter, 
             attributes      AttributeSelection } 
    
        AttributeSelection ::= SEQUENCE OF selector LDAPString 
                        -- The LDAPString is constrained to 
                        -- <attributeSelector> below 
    
        Filter ::= CHOICE { 
             and             [0] SET OF filter Filter, 
             or              [1] SET OF filter Filter, 
             not             [2] Filter, 
             equalityMatch   [3] AttributeValueAssertion, 
             substrings      [4] SubstringFilter, 
             greaterOrEqual  [5] AttributeValueAssertion, 
  
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             lessOrEqual     [6] AttributeValueAssertion, 
             present         [7] AttributeDescription, 
             approxMatch     [8] AttributeValueAssertion, 
             extensibleMatch [9] MatchingRuleAssertion } 
    
        SubstringFilter ::= SEQUENCE { 
             type           AttributeDescription, 
             -- initial and final can occur at most once 
             substrings     SEQUENCE SIZE (1..MAX) OF substring CHOICE { 
                  initial [0] AssertionValue, 
                  any     [1] AssertionValue, 
                  final   [2] AssertionValue } } 
    
        MatchingRuleAssertion ::= SEQUENCE { 
             matchingRule    [1] MatchingRuleId OPTIONAL, 
             type            [2] AttributeDescription OPTIONAL, 
             matchValue      [3] AssertionValue, 
             dnAttributes    [4] BOOLEAN DEFAULT FALSE } 
    
   Fields of the Search Request are: 
    
   - baseObject: The name of the base object entry relative to which 
     the search is to be performed. 
    
   - scope: Specifies the scope of the search to be performed. The 
     semantics (as described in [X.511]) of the possible values of this 
     field are: 
        
        baseObject:  The scope is constrained to the entry named by 
        baseObject. 
         
        singleLevel: The scope is constrained to the immediate 
        subordinates of the entry named by baseObject. 
         
        wholeSubtree: the scope is constrained to the entry named by 
        the baseObject, and all its subordinates. 
    
    
   - derefAliases: An indicator as to how alias entries (as defined in 
     [Models]) are to be handled in searching. The semantics of the 
     possible values of this field are: 
    
        neverDerefAliases: Do not dereference aliases in searching or 
        in locating the base object of the search. 
         
        derefInSearching: While searching, dereference any alias entry 
        subordinate to the base object which is also in the search 
        scope. The filter is applied to the dereferenced object(s). If 
        the search scope is wholeSubtree, the search continues in the 
        subtree of any dereferenced object. Aliases in that subtree are 
        also dereferenced. Servers SHOULD eliminate duplicate entries 
        that arise due to alias dereferencing while searching. 
         


  
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        derefFindingBaseObj: Dereference aliases in locating the base 
        object of the search, but not when searching subordinates of 
        the base object. 
         
        derefAlways: Dereference aliases both in searching and in 
        locating the base object of the search. 
     Servers MUST detect looping while dereferencing aliases in order 
     to prevent denial of service attacks of this nature. 
    
   - sizeLimit: A size limit that restricts the maximum number of 
     entries to be returned as a result of the search. A value of zero 
     in this field indicates that no client-requested size limit 
     restrictions are in effect for the search. Servers may also 
     enforce a maximum number of entries to return. 
    
   - timeLimit: A time limit that restricts the maximum time (in 
     seconds) allowed for a search. A value of zero in this field 
     indicates that no client-requested time limit restrictions are in 
     effect for the search. Servers may also enforce a maximum time 
     limit for the search. 
    
   - typesOnly: An indicator as to whether search results are to 
     contain both attribute descriptions and values, or just attribute 
     descriptions. Setting this field to TRUE causes only attribute 
     descriptions (no values) to be returned. Setting this field to 
     FALSE causes both attribute descriptions and values to be 
     returned. 
    
   - filter: A filter that defines the conditions that must be 
     fulfilled in order for the search to match a given entry. 
      
     The 'and', 'or' and 'not' choices can be used to form combinations 
     of filters. At least one filter element MUST be present in an 
     'and' or 'or' choice. The others match against individual 
     attribute values of entries in the scope of the search. 
     (Implementor's note: the 'not' filter is an example of a tagged 
     choice in an implicitly-tagged module. In BER this is treated as 
     if the tag was explicit.) 
    
     A server MUST evaluate filters according to the three-valued logic 
     of X.511 (1993) Section 7.8.1. In summary, a filter is evaluated 
     to either "TRUE", "FALSE" or "Undefined". If the filter evaluates 
     to TRUE for a particular entry, then the attributes of that entry 
     are returned as part of the search result (subject to any 
     applicable access control restrictions). If the filter evaluates 
     to FALSE or Undefined, then the entry is ignored for the search. 
      
     A filter of the "and" choice is TRUE if all the filters in the SET 
     OF evaluate to TRUE, FALSE if at least one filter is FALSE, and 
     otherwise Undefined. A filter of the "or" choice is FALSE if all 
     of the filters in the SET OF evaluate to FALSE, TRUE if at least 
     one filter is TRUE, and Undefined otherwise. A filter of the 'not' 
     choice is TRUE if the filter being negated is FALSE, FALSE if it 
     is TRUE, and Undefined if it is Undefined. 
  
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     The present match evaluates to TRUE where there is an attribute or 
     subtype of the specified attribute description present in an 
     entry, and FALSE otherwise (including a presence test with an 
     unrecognized attribute description.) 
      
     The matching rule for equalityMatch filter items is defined by the 
     EQUALITY matching rule for the attribute type. 
    
     There SHALL be at most one 'initial', and at most one 'final' in 
     the 'substrings' of a SubstringFilter. If 'initial' is present, it 
     SHALL be the first element of 'substrings'. If 'final' is present, 
     it SHALL be the last element of 'substrings'.  
     The matching rule for AssertionValues in a substrings filter item 
     is defined by the SUBSTR matching rule for the attribute type. 
     Note that the AssertionValue in a substrings filter item conforms 
     to the assertion syntax of the EQUALITY matching rule for the 
     attribute type rather than the assertion syntax of the SUBSTR 
     matching rule for the attribute type. Conceptually, the entire 
     SubstringFilter is converted into an assertion value of the 
     substrings matching rule prior to applying the rule. 
    
     The matching rule for the greaterOrEqual filter item is defined by 
     the ORDERING and EQUALITY matching rules for the attribute type. 
    
     The matching rule for the lessOrEqual filter item is defined by 
     the ORDERING matching rule for the attribute type. 
    
     An approxMatch filter item evaluates to TRUE when there is a value 
     of the attribute or subtype for which some locally-defined 
     approximate matching algorithm (e.g. spelling variations, phonetic 
     match, etc.) returns TRUE. If an item matches for equality, it 
     also satisfies an approximate match. If approximate matching is 
     not supported for the attribute, this filter item should be 
     treated as an equalityMatch. 
      
     An extensibleMatch filter item is evaluated as follows: 
    
        If the matchingRule field is absent, the type field MUST be 
        present, and an equality match is performed for that type. 
         
        If the type field is absent and the matchingRule is present, the 
        matchValue is compared against all attributes in an entry which 
        support that matchingRule. The matchingRule determines the 
        syntax for the assertion value. The filter item evaluates to 
        TRUE if it matches with at least one attribute in the entry, 
        FALSE if it does not match any attribute in the entry, and 
        Undefined if the matchingRule is not recognized or the 
        assertionValue is invalid.  
         
        If the type field is present and the matchingRule is present, 
        the matchValue is compared against entry attributes of the 
        specified type. In this case, the matchingRule MUST be one 


  
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        suitable for use with the specified type (see [Syntaxes]), 
        otherwise the filter item is Undefined.  
         
        If the dnAttributes field is set to TRUE, the match is 
        additionally applied against all the AttributeValueAssertions in 
        an entry's distinguished name, and evaluates to TRUE if there is 
        at least one attribute in the distinguished name for which the 
        filter item evaluates to TRUE. The dnAttributes field is present 
        to alleviate the need for multiple versions of generic matching 
        rules (such as word matching), where one applies to entries and 
        another applies to entries and dn attributes as well. 
         
     A filter item evaluates to Undefined when the server would not be 
     able to determine whether the assertion value matches an entry. 
     Examples include:  
      
     - An attribute description in an equalityMatch, substrings, 
       greaterOrEqual, lessOrEqual, approxMatch or extensibleMatch 
       filter is not recognized by the server. 
      
     - The attribute type does not define the appropriate matching 
       rule. 
      
     - A MatchingRuleId in the extensibleMatch is not recognized by 
       the server or is not valid for the attribute type. 
      
     - The type of filtering requested is not implemented. 
      
     - The assertion value is invalid.  
    
     For example, if a server did not recognize the attribute type 
     shoeSize, a filter of (shoeSize=*) would evaluate to FALSE, and 
     the filters (shoeSize=12), (shoeSize>=12) and (shoeSize<=12) would 
     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 Section 7.8 of [X.511]. 
    
   - attributes: A selection list of the attributes to be returned from 
     each entry which matches the search filter. LDAPString values of 
     this field are constrained to the following Augmented Backus-Naur 
     Form ([ABNF]): 
    
     attributeSelector = attributedescription / selectorpecial 
    
     selectorspecial = noattrs / alluserattrs 
    
     noattrs = %x31.2E.31 ; "1.1" 
    
     alluserattrs = %x2A ; asterisk ("*") 
    


  
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     The <attributedescription> production is defined in Section 2.5 of 
     [Models]. 
    
     There are three special cases which may appear in the attributes 
     selection list:  
        
     - an empty list with no attributes,  
        
     - a list containing "*" (with zero or more attribute 
       descriptions), and  
                                          
     - a list containing only "1.1".  
        
     An empty list requests the return of all user attributes.   
        
     A list containing "*" requests the return of all user attributes 
     in addition to other listed (operational) attributes.   
        
     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 [Models]. 
    
     Attributes are returned at most once in an entry. If an attribute 
     description is named more than once in the list, the subsequent 
     names are ignored. If an attribute description in the list is not 
     recognized, it is ignored by the server. 
      
   Note that an X.500 "list"-like operation can be emulated by the 
   client requesting a one-level LDAP search operation with a filter 
   checking for the presence of the 'objectClass' attribute, and that an 
   X.500 "read"-like operation can be emulated by a base object LDAP 
   search operation with the same filter. A server which provides a 
   gateway to X.500 is not required to use the Read or List operations, 
   although it may choose to do so, and if it does, it must provide the 
   same semantics as the X.500 search operation. 
    
    
4.5.2. Search Result 
    
   The results of the search operation are returned as zero or more 
   searchResultEntry messages, zero or more SearchResultReference 
   messages, followed by a single searchResultDone message. 
    
        SearchResultEntry ::= [APPLICATION 4] SEQUENCE { 
  
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             objectName      LDAPDN, 
             attributes      PartialAttributeList } 
    
        PartialAttributeList ::= SEQUENCE OF  
                             partialAttribute PartialAttribute   
        -- Note that the PartialAttributeList may hold zero elements. 
        -- This may happen when none of the attributes of an entry 
        -- were requested, or could be returned. 
        -- Note also that the partialAttribute vals set may hold zero 
        -- elements. This may happen when typesOnly is requested, access 
        -- controls prevent the return of values, or other reasons. 
    
        SearchResultReference ::= [APPLICATION 19] SEQUENCE  
                                  SIZE (1..MAX) OF uri URI 
    
        SearchResultDone ::= [APPLICATION 5] LDAPResult 
    
   Each SearchResultEntry represents an entry found during the search. 
   Each SearchResultReference represents an area not yet explored during 
   the search. The SearchResultEntry and SearchResultReference PDUs may 
   come in any order. Following all the SearchResultReference and 
   SearchResultEntry responses, the server returns a SearchResultDone 
   response, which contains an indication of success, or detailing any 
   errors that have occurred. 
    
   Each entry returned in a SearchResultEntry will contain all 
   appropriate attributes as specified in the attributes field of the 
   Search Request. Return of attributes is subject to access control and 
   other administrative policy. 
    
   Some attributes may be constructed by the server and appear in a 
   SearchResultEntry attribute list, although they are not stored 
   attributes of an entry. Clients SHOULD NOT assume that all attributes 
   can be modified, even if permitted by access control. 
    
   If the server's schema defines short names [Models] for an attribute 
   type then the server SHOULD use one of those names in attribute 
   descriptions for that attribute type (in preference to using the 
   <numericoid> [Models] format of the attribute type's object 
   identifier). The server SHOULD NOT use the short name if that name is 
   known by the server to be ambiguous, or otherwise likely to cause 
   interoperability problems. 
    
    
4.5.3. Continuation References in the Search Result 
    
   If the server was able to locate the entry referred to by the 
   baseObject but was unable to search one or more non-local entries, 
   the server may return one or more SearchResultReference entries, each 
   containing a reference to another set of servers for continuing the 
   operation. A server MUST NOT return any SearchResultReference if it 
   has not located the baseObject and thus has not searched any entries; 
   in this case it would return a SearchResultDone containing either a 


  
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   referral or noSuchObject result code (depending on the server's 
   knowledge of the entry named in the baseObject). 
    
   If a server holds a copy or partial copy of the subordinate naming 
   context [Section 5 of Models], it may use the search filter to 
   determine whether or not to return a SearchResultReference response. 
   Otherwise SearchResultReference responses are always returned when in 
   scope. 
    
   The SearchResultReference is of the same data type as the Referral.  
    
   A URI for a server implementing LDAP and accessible via [TCP]/[IP] 
   (v4 or v6) is written as an LDAP URL according to [LDAPURL].  
    
   In order to complete the search, the client issues a new search 
   operation for each SearchResultReference that is returned. Note that 
   the abandon operation described in Section 4.11 applies only to a 
   particular operation sent on the LDAP exchange between a client and 
   server. The client must abandon subsequent search operations it 
   wishes to individually.  
    
   Clients that follow search continuation references MUST ensure that 
   they do not loop between servers. They MUST NOT repeatedly contact 
   the same server for the same request with the same target entry name, 
   scope and filter. Some clients use a counter that is incremented each 
   time search result reference handling occurs for an operation, and 
   these kinds of clients MUST be able to handle at least ten nested 
   search result references between the root and a leaf entry. 
    
   When an LDAP URL is used, the following instructions are followed: 
    
   - The <dn> part of the URL MUST be present, with the new target 
     object name. The client MUST use this name when following the 
     reference. UTF-8 encoded characters appearing in the string 
     representation of a DN or search filter may not be legal for URLs 
     (e.g. spaces) and MUST be escaped using the % method in [URI].  
    
   - Some servers (e.g. participating in distributed indexing) may 
     provide a different filter in a URL of a SearchResultReference. 
    
   - If the <filter> part of the URL is present, the client MUST use 
     this filter in its next request to progress this search, and if it 
     is not present the client MUST use the same filter as it used for 
     that search.  
    
   - If the originating search scope was singleLevel, the <scope> part 
     of the URL will be "base". 
    
   - It is RECOMMENDED that the <scope> part be present to avoid 
     ambiguity. 
    
   - Other aspects of the new search request may be the same as or 
     different from the search request which generated the 
     SearchResultReference. 
  
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   - The name of an unexplored subtree in a SearchResultReference need 
     not be subordinate to the base object. 
 
   Other kinds of URIs may be returned. The syntax and semantics of such 
   URIs is left to future specifications. Clients may ignore URIs that 
   they do not support. 
 
    
4.5.3.1. Examples 
    
   For example, suppose the contacted server (hosta) holds the entry 
   <DC=Example,DC=NET> and the entry <CN=Manager,DC=Example,DC=NET>. It 
   knows that either LDAP-capable servers (hostb) or (hostc) hold 
   <OU=People,DC=Example,DC=NET> (one is the master and the other server 
   a shadow), and that LDAP-capable server (hostd) holds the subtree 
   <OU=Roles,DC=Example,DC=NET>. If a wholeSubtree search of 
   <DC=Example,DC=NET> is requested to the contacted server, it may 
   return the following: 
    
     SearchResultEntry for DC=Example,DC=NET 
     SearchResultEntry for CN=Manager,DC=Example,DC=NET 
     SearchResultReference { 
       ldap://hostb/OU=People,DC=Example,DC=NET??sub 
       ldap://hostc/OU=People,DC=Example,DC=NET??sub } 
     SearchResultReference { 
       ldap://hostd/OU=Roles,DC=Example,DC=NET??sub } 
     SearchResultDone (success) 
    
   Client implementors should note that when following a 
   SearchResultReference, additional SearchResultReference may be 
   generated. Continuing the example, if the client contacted the server 
   (hostb) and issued the search for the subtree 
   <OU=People,DC=Example,DC=NET>, the server might respond as follows: 
    
     SearchResultEntry for OU=People,DC=Example,DC=NET 
     SearchResultReference { 
       ldap://hoste/OU=Managers,OU=People,DC=Example,DC=NET??sub } 
     SearchResultReference { 
       ldap://hostf/OU=Consultants,OU=People,DC=Example,DC=NET??sub } 
     SearchResultDone (success) 
    
   Similarly, if a singleLevel search of <DC=Example,DC=NET> is 
   requested to the contacted server, it may return the following: 
    
     SearchResultEntry for CN=Manager,DC=Example,DC=NET 
     SearchResultReference { 
       ldap://hostb/OU=People,DC=Example,DC=NET??base 
       ldap://hostc/OU=People,DC=Example,DC=NET??base } 
     SearchResultReference { 
       ldap://hostd/OU=Roles,DC=Example,DC=NET??base } 
     SearchResultDone (success) 
    


  
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   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: 
    
   - object: The name of the object to be modified. The value of this 
     field contains the DN of the entry to be modified. The server 
     SHALL NOT perform any alias dereferencing in determining the 
     object to be modified. 
    
   - changes: A list of modifications to be performed on the entry. The 
     entire list of modifications MUST be performed in the order they 
     are listed as a single atomic operation. While individual 
     modifications may violate certain aspects of the directory schema 
     (such as the object class definition and DIT content rule), the 
     resulting entry after the entire list of modifications is 
     performed MUST conform to the requirements of the directory model 
     and controlling schema [Models]. 
         
     -  operation: Used to specify the type of modification being 
        performed. Each operation type acts on the following 
        modification. The values of this field have the following 
        semantics respectively: 
    
           add: add values listed to the modification attribute, 
           creating the attribute if necessary; 
            
           delete: delete values listed from the modification attribute, 
           removing the entire attribute if no values are listed, or if 
           all current values of the attribute are listed for deletion; 
            


  
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           replace: replace all existing values of the modification 
           attribute with the new values listed, creating the attribute 
           if it did not already exist. A replace with no value will 
           delete the entire attribute if it exists, and is ignored if 
           the attribute does not exist. 
    
     -  modification: A PartialAttribute (which may have an empty SET 
        of vals) used to hold the attribute type or attribute type and 
        values being modified. 
    
   Upon receipt of a Modify Request, the server attempts to perform the 
   necessary modifications to the DIT and returns the result in a Modify 
   Response, defined as follows: 
    
        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. The result of the modification is indeterminate if the 
   Modify Response is not received (e.g. the LDA exchange is terminated 
   or the Modify Operation is abandoned). 
    
   The Modify Operation cannot be used to remove from an entry any of 
   its distinguished values, i.e. those values which form the entry's 
   relative distinguished name. An attempt to do so will result in the 
   server returning the notAllowedOnRDN result code. The Modify DN 
   Operation described in Section 4.9 is used to rename an entry. 
    
   Note that due to the simplifications made in LDAP, there is not a 
   direct mapping of the changes in an LDAP ModifyRequest onto the 
   changes of a DAP ModifyEntry operation, and different implementations 
   of LDAP-DAP gateways may use different means of representing the 
   change. If successful, the final effect of the operations on the 
   entry MUST be identical. 
    
    
4.7. Add Operation 
    
   The Add Operation allows a client to request the addition of an entry 
   into the Directory. The Add Request is defined as follows: 
    
        AddRequest ::= [APPLICATION 8] SEQUENCE { 
             entry           LDAPDN, 
             attributes      AttributeList } 
    
        AttributeList ::= SEQUENCE OF attribute Attribute 
    
   Fields of the Add Request are: 
  
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   - entry: the name of the entry to be added. The server SHALL NOT 
     dereference any aliases in locating the entry to be added. 
    
   - attributes: the list of attributes that, along with those from the 
     RDN, make up the content of the entry being added. Clients MAY or 
     MAY NOT include the RDN attribute in this list. Clients MUST 
     include the 'objectClass' attribute, and values of any mandatory 
     attributes of the listed object classes. Clients MUST NOT supply 
     NO-USER-MODIFICATION attributes such as the createTimestamp or 
     creatorsName attributes, since the server maintains these 
     automatically. 
    
   The entry named in the entry field of the AddRequest MUST NOT exist 
   for the AddRequest to succeed. The immediate superior (parent) of an 
   object or alias entry to be added MUST exist. For example, if the 
   client attempted to add <CN=JS,DC=Example,DC=NET>, the 
   <DC=Example,DC=NET> entry did not exist, and the <DC=NET> entry did 
   exist, then the server would return the noSuchObject result code with 
   the matchedDN field containing <DC=NET>.  
    
   Server implementations SHOULD NOT restrict where entries can be 
   located in the Directory unless DIT structure rules are in place. 
   Some servers allow the administrator to restrict the classes of 
   entries which can be added to the Directory. 
    
   Upon receipt of an Add Request, a server will attempt to add the 
   requested entry. The result of the add attempt will be returned to 
   the client in the Add Response, defined as follows: 
    
        AddResponse ::= [APPLICATION 9] LDAPResult 
    
   A response of success indicates that the new entry has been added to 
   the Directory. 
    
    
4.8. Delete Operation 
    
   The Delete Operation allows a client to request the removal of an 
   entry from the Directory. The Delete Request is defined as follows: 
    
        DelRequest ::= [APPLICATION 10] LDAPDN 
    
   The Delete Request consists of the name of the entry to be deleted. 
   The server SHALL NOT dereference aliases while resolving the name of 
   the target entry to be removed. 
    
   Only leaf entries (those with no subordinate entries) can be deleted 
   with this operation. 
    
   Upon receipt of a Delete Request, a server will attempt to perform 
   the entry removal requested and return the result in the Delete 
   Response defined as follows: 
    
  
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        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: 
    
   - entry: the name of the entry to be changed. This entry may or may 
     not have subordinate entries. 
    
   - newrdn: the new RDN of the entry. If the operation moves the entry 
     to a new superior without changing its RDN, the value of the old 
     RDN is supplied for this parameter. 
     Attribute values of the new RDN not matching any attribute value 
     of the entry are added to the entry and an appropriate error is 
     returned if this fails. 
     
   - deleteoldrdn: a boolean field that controls whether the old RDN 
     attribute values are to be retained as attributes of the entry, or 
     deleted from the entry. 
    
   - newSuperior: if present, this is the name of an existing object 
     entry which becomes the immediate superior (parent) of the 
     existing entry. 
    
   The server SHALL NOT dereference any aliases in locating the objects 
   named in entry or newSuperior. 
    
   Upon receipt of a ModifyDNRequest, a server will attempt to perform 
   the name change and return the result in the Modify DN Response, 
   defined as follows: 
    
        ModifyDNResponse ::= [APPLICATION 13] LDAPResult 
    
   For example, if the entry named in the entry field was <cn=John 
   Smith,c=US>, the newrdn field was <cn=John Cougar Smith>, and the 
   newSuperior field was absent, then this operation would attempt to 
   rename the entry to be <cn=John Cougar Smith,c=US>. If there was 
   already an entry with that name, the operation would fail with the 
   entryAlreadyExists result code. 
    
   The object named in newSuperior MUST exist. For example, if the 
   client attempted to add <CN=JS,DC=Example,DC=NET>, the 
  
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   <DC=Example,DC=NET> entry did not exist, and the <DC=NET> entry did 
   exist, then the server would return the noSuchObject result code with 
   the matchedDN field containing <DC=NET>. 
 
   If the deleteoldrdn field is TRUE, the attribute values forming the 
   old RDN but not the new RDN are deleted from the entry. If the 
   deleteoldrdn field is FALSE, the attribute values forming the old RDN 
   will be retained as non-distinguished attribute values of the entry. 
   The server MUST fail the operation and return an error in the result 
   code if the setting of the deleteoldrdn field would cause a schema 
   inconsistency in the entry. 
    
   Note that X.500 restricts the ModifyDN operation to only affect 
   entries that are contained within a single server. If the LDAP server 
   is mapped onto DAP, then this restriction will apply, and the 
   affectsMultipleDSAs result code will be returned if this error 
   occurred. In general, clients MUST NOT expect to be able to perform 
   arbitrary movements of entries and subtrees between servers or 
   between naming contexts. 
    
    
4.10. Compare Operation 
    
   The Compare Operation allows a client to compare an assertion value 
   with the values of a particular attribute in a particular entry in 
   the Directory. The Compare Request is defined as follows: 
    
        CompareRequest ::= [APPLICATION 14] SEQUENCE { 
             entry           LDAPDN, 
             ava             AttributeValueAssertion } 
    
   Fields of the Compare Request are: 
    
   - entry: the name of the entry to be compared. The server SHALL NOT 
     dereference any aliases in locating the entry to be compared. 
    
   - ava: holds the attribute value assertion to be compared. 
    
   Upon receipt of a Compare Request, a server will attempt to perform 
   the requested comparison and return the result in the Compare 
   Response, defined as follows: 
    
        CompareResponse ::= [APPLICATION 15] LDAPResult 
    
   The resultCode field is set to compareTrue, compareFalse, or an 
   appropriate error. compareTrue indicates that the assertion value in 
   the ava field matches a value of the attribute or subtype according 
   to the attribute's EQUALITY matching rule. compareFalse indicates 
   that the assertion value in the ava field and the values of the 
   attribute or subtype did not match. Other result codes indicate 
   either that the result of the comparison was Undefined (Section 
   4.5.1), or that some error occurred. 
    


  
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   Note that some directory systems may establish access controls which 
   permit the values of certain attributes (such as userPassword) to be 
   compared but not 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 which was requested earlier in 
   this LDAP exchange. The abandon request itself has its own MessageID. 
   This is distinct from the MessageID of the earlier operation being 
   abandoned. 
    
   There is no response defined in the Abandon operation. Upon receipt 
   of an AbandonRequest, the server MAY abandon the operation identified 
   by the MessageID. Since the client cannot tell the difference between 
   a successfully abandoned operation and an uncompleted operation, the 
   application of the Abandon operation is limited to uses where the 
   client does not require an indication of its outcome. 
    
   Abandon, Bind, Unbind, and StartTLS operations cannot be abandoned.  
    
   In the event that a server receives an Abandon Request on a Search 
   Operation in the midst of transmitting responses to the search, that 
   server MUST cease transmitting entry responses to the abandoned 
   request immediately, and MUST NOT send the SearchResponseDone. Of 
   course, the server MUST ensure that only properly encoded LDAPMessage 
   PDUs are transmitted. 
    
   The ability to abandon other (particularly update) operations is at 
   the discretion of the server.  
    
   Clients should not send abandon requests for the same operation 
   multiple times, and MUST also be prepared to receive results from 
   operations it has abandoned (since these may have been in transit 
   when the abandon was requested, or are not able to be abandoned). 
    
   Servers MUST discard abandon requests for message IDs they do not 
   recognize, for operations which cannot be abandoned, and for 
   operations which have already been abandoned. 
    
    
4.12. Extended Operation 
    
   The extended operation allows additional operations to be defined for 
   services not already available in the protocol. For example, to add 
   operations to install transport layer security (see Section 4.14). 
    


  
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   The extended operation allows clients to make requests and receive 
   responses with predefined syntaxes and semantics. These may be 
   defined in RFCs or be private to particular implementations.  
    
   Each extended operation consists of an extended request and an 
   extended response.  
    
        ExtendedRequest ::= [APPLICATION 23] SEQUENCE { 
             requestName      [0] LDAPOID, 
             requestValue     [1] OCTET STRING OPTIONAL } 
    
   The requestName is a dotted-decimal representation of the unique 
   OBJECT IDENTIFIER corresponding to the request. The requestValue is 
   information in a form defined by that request, encapsulated inside an 
   OCTET STRING. 
    
   The server will respond to this with an LDAPMessage containing an 
   ExtendedResponse. 
    
        ExtendedResponse ::= [APPLICATION 24] SEQUENCE { 
             COMPONENTS OF LDAPResult, 
             responseName     [10] LDAPOID OPTIONAL, 
             responseValue    [11] OCTET STRING OPTIONAL } 
    
   The responseName is typically not required to be present as the 
   syntax and semantics of the response (including the format of the 
   responseValue) is implicitly known and associated with the request by 
   the messageID. 
    
   If the extended operation associated with the requestName is not 
   supported by the server, the server MUST NOT provide a responseName 
   nor a responseValue and MUST return a resultCode of protocolError. 
    
   The requestValue and responseValue fields contain any information 
   associated with the operation. The format of these fields is defined 
   by the specification of the extended operation. Implementations MUST 
   be prepared to handle arbitrary contents of these fields, including 
   zero bytes. Values that are defined in terms of ASN.1 and BER encoded 
   according to Section 5.2, also follow the extensibility rules in 
   Section 4. 
    
   Servers list the requestName of Extended Requests they recognize in 
   the 'supportedExtension' attribute in the root DSE (Section 5.1 of 
   [Models]). 
 
   Extended operations may be specified in other documents. The 
   specification of an extended operation consists of: 
    
   - the OBJECT IDENTIFIER assigned to the requestName, 
    
   - the OBJECT IDENTIFIER (if any) assigned to the responseName (note 
     that the same OBJECT IDENTIFIER my be used for both the 
     requestName and responseName), 
    
  
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   - the format of the contents of the requestValue and responseValue 
     (if any), and 
    
   - the semantics of the operation. 
 
 
4.13. IntermediateResponse Message 
    
   While the Search operation provides a mechanism to return multiple 
   response messages for a single search request, other operations, by 
   nature, do not provide for multiple response messages. 
    
   The IntermediateResponse message provides a general mechanism for 
   defining single-request/multiple-response operations in LDAP. This 
   message is intended to be used in conjunction with the extended 
   operation to define new single-request/multiple-response operations 
   or in conjunction with a control when extending existing LDAP 
   operations in a way that requires them to return intermediate 
   response information.  
    
   It is intended that the definitions and descriptions of extended 
   operations and controls that make use of the IntermediateResponse 
   message will define the circumstances when an IntermediateResponse 
   message can be sent by a server and the associated meaning of an 
   IntermediateResponse message sent in a particular circumstance. 
    
        IntermediateResponse ::= [APPLICATION 25] SEQUENCE { 
                responseName     [0] LDAPOID OPTIONAL, 
                responseValue    [1] OCTET STRING OPTIONAL } 
    
   IntermediateResponse messages SHALL NOT be returned to the client 
   unless the client issues a request that specifically solicits their 
   return. This document defines two forms of solicitation: extended 
   operation and request control. IntermediateResponse messages are 
   specified in documents describing the manner in which they are 
   solicited (i.e. in the extended operation or request control 
   specification that uses them). These specifications include: 
        
   - the OBJECT IDENTIFIER (if any) assigned to the responseName, 
    
   - the format of the contents of the responseValue, and 
    
   - the semantics associated with the IntermediateResponse message.  
    
   Extensions that allow the return of multiple types of 
   IntermediateResponse messages SHALL identify those types using unique 
   responseName values (note that one of these may specify no value). 
    
   Sections 4.13.1 and 4.13.2 describe additional requirements on the 
   inclusion of responseName and responseValue in IntermediateResponse 
   messages.  
 
  
4.13.1. Usage with LDAP ExtendedRequest and ExtendedResponse  
  
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   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: 
    
   - two or more controls using IntermediateResponse messages are 
     included in a request for any LDAP operation or   
        
   - one or more controls using IntermediateResponse messages are 
     included in a request with an LDAP extended operation that uses 
     IntermediateResponse messages. 
    
    
4.14. StartTLS Operation 
 
   The Start Transport Layer Security (StartTLS) operations 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 PDU to the server. The StartTLS request is defined in terms 
   of an ExtendedRequest. The requestName is "1.3.6.1.4.1.1466.20037", 
   and the requestValue field is always absent.  
    
   The client MUST NOT send any PDUs on this LDAP exchange following 
   this request until it receives a StartTLS extended response and, in 
   the case of a successful response, completes TLS negotiations. 
    
   Sequencing problems (particularly those detailed in Section 3.1.1 of 
   [AuthMeth] result in an operationsError being returned in the 
   resultCode. 
    
   If the server does not support TLS (whether by design or by current 
   configuration), it returns the protocolError resultCode as described 
   in Section 4.12. 
  
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4.14.2. StartTLS Response 
 
   When a StartTLS request is made, servers supporting the operation 
   MUST return a StartTLS response PDU to the requestor. The 
   responseName, if present, is also "1.3.6.1.4.1.1466.20037". The 
   responseValue is absent.  
    
   If the server is willing and able to negotiate TLS, it returns a 
   success resultCode. Refer to Section 4 of [AuthMeth] for details. 
 
   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 return indicate 
   so by returning the unavailable resultCode. 
 
 
4.14.3. Removal of the TLS Layer 
 
   Two forms of TLS layer removal -- graceful and abrupt -- are 
   provided. These do not involve LDAP PDUs, but are preformed at the 
   underlying layers. 
    
   If the connection is closed, uncompleted operations are handled as 
   specified in Section 5.1. 
    
    
4.14.3.1. Graceful Removal 
 
   Either the client or server MAY remove the TLS layer and leave the 
   LDAP exchange intact by sending and receiving a TLS closure alert. 
    
   The initiating protocol peer sends the TLS closure alert. If it 
   wishes to leave the LDAP exchange intact, it then MUST cease to send 
   further PDUs and MUST ignore any received LDAP PDUs until it receives 
   a TLS closure alert from the other peer.  
    
   Once the initiating protocol peer receives a TLS closure alert from 
   the other peer it MAY send and receive LDAP PDUs. 
    
   When a protocol peer receives the initial TLS closure alert, it may 
   choose to allow the LDAP exchange to remain intact. In this case, it 
   MUST immediately transmit a TLS closure alert. Following this, it MAY 
   send and receive LDAP PDUs. 
    
   Protocol peers MAY close the connection after sending or receiving a 
   TLS closure alert. 
 
   After the TLS layer has been removed, the server MUST NOT send 
   responses to any request message received before the TLS closure 
  
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   alert. Thus, clients wishing to receive responses to messages sent 
   while the TLS layer is intact MUST wait for those message responses 
   before sending the TLS closure alert.  
    
    
4.14.3.2. Abrupt Removal 
 
   Either the client or server MAY abruptly remove the TLS layer by 
   closing the connection. In this circumstance, a server MAY send the 
   client a Notice of Disconnection before closing the connection.  
    
    
5. Protocol Encoding, Connection, and Transfer 
    
   This protocol is designed to run over connection-oriented, reliable 
   transports, where the data stream is divided into octets (8-bit 
   units), with each octet and each bit being significant. 
    
   One underlying service, LDAP over TCP, is defined in Section 
   5.3. This service is generally applicable to applications providing 
   or consuming X.500-based directory services on the Internet. This 
   specification was generally written with the TCP mapping in mind. 
   Specifications detailing other mappings may encounter various 
   obstacles. 
    
   Implementations of LDAP over TCP MUST implement the mapping as 
   described in Section 5.3. 
    
   This table illustrates the relationship between the different layers 
   involved in an exchange between two protocol peers: 
    
               +---------------+ 
               | LDAP exchange | 
               +---------------+ > LDAP PDUs 
               +---------------+ < data        
               |   SASL layer  |              
               +---------------+ > SASL-protected data 
               +---------------+ < data     
               |   TLS layer   |           
   Application +---------------+ > TLS-protected data 
   ------------+---------------+ < data   
     Transport |   connection  |         
               +---------------+  
    
 
5.2. Protocol Encoding 
    
   The protocol elements of LDAP SHALL be encoded for exchange using the 
   Basic Encoding Rules [BER] of [ASN.1] with the following 
   restrictions: 
    
   - Only the definite form of length encoding is used. 
    
  
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   - OCTET STRING values are encoded in the primitive form only. 
    
   - If the value of a BOOLEAN type is true, the encoding of the value 
     octet is set to hex "FF". 
    
   - If a value of a type is its default value, it is absent. Only some 
     BOOLEAN and INTEGER types have default values in this protocol 
     definition. 
    
   These restrictions are meant to ease the overhead of encoding and 
   decoding certain elements in BER. 
    
   These restrictions do not apply to ASN.1 types encapsulated inside of 
   OCTET STRING values, such as attribute values, unless otherwise 
   stated. 
    
 
5.3. Transmission Control Protocol (TCP) 
    
   The encoded LDAPMessage PDUs are mapped directly onto the [TCP] 
   bytestream using the BER-based encoding described in Section 5.2. It 
   is recommended that server implementations running over the TCP 
   provide a protocol listener on the Internet Assigned Numbers 
   Authority (IANA)-assigned LDAP port, 389 [PortReg]. Servers may 
   instead provide a listener on a different port number. Clients MUST 
   support contacting servers on any valid TCP port. 
    
    
6. Security Considerations 
    
   This version of the protocol provides facilities for simple 
   authentication using a cleartext password, as well as any [SASL] 
   mechanism. Installing SASL layers can provide integrity and other 
   data security services. 
    
   It is also permitted that the server can return its credentials to 
   the client, if it chooses to do so. 
    
   Use of cleartext password is strongly discouraged where the 
   underlying transport service cannot guarantee confidentiality and may 
   result in disclosure of the password to unauthorized parties. 
    
   Servers are encouraged to prevent directory modifications by clients 
   that have authenticated anonymously [AuthMeth].  
    
   Security considerations for authentication methods, SASL mechanisms, 
   and TLS are described in [AuthMeth]. 
    
   It should be noted that SASL authentication exchanges do not provide 
   data confidentiality nor integrity protection for the version or name 
   fields of the bind request nor the resultCode, diagnosticMessage, or 
   referral fields of the bind response nor of any information contained 
   in controls attached to bind request or responses. Thus information 
   contained in these fields SHOULD NOT be relied on unless otherwise 
  
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              Lightweight Directory Access Protocol Version 3 
                                      
   protected (such as by establishing protections at the transport 
   layer).  
         
   Server implementors should plan for the possibility of (protocol or 
   external) events which alter the information used to establish 
   security factors (e.g., credentials, authorization identities, access 
   controls) during the course of the LDAP exchange, and even during the 
   performance of a particular operation, and should take steps to avoid 
   insecure side effects of these changes.  The ways in which these 
   issues are addressed are application and/or implementation specific. 
    
   Implementations which cache attributes and entries obtained via LDAP 
   MUST ensure that access controls are maintained if that information 
   is to be provided to multiple clients, since servers may have access 
   control policies which prevent the return of entries or attributes in 
   search results except to particular authenticated clients. For 
   example, caches could serve result information only to the client 
   whose request caused it to be in the cache. 
    
   Servers may return referrals or search result references which 
   redirect clients to peer servers. It is possible for a rogue 
   application to inject such referrals into the data stream in an 
   attempt to redirect a client to a rogue server. Clients are advised 
   to be aware of this, and possibly reject referrals when 
   confidentiality measures are not in place. Clients are advised to 
   reject referrals from the StartTLS operation. 
    
   The matchedDN and diagnosticMessage fields, as well as some 
   resultCode values (e.g., attributeOrValueExists and 
   entryAlreadyExists), could disclose the presence the specific data in 
   the directory which is subject to access and other administrative 
   controls. Server implementations should restrict access to protected 
   information equally under both normal and error conditions. 
    
   Protocol peers MUST be prepared to handle invalid and arbitrary 
   length protocol encodings. 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. 
    
    
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. 
    
  
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              Lightweight Directory Access Protocol Version 3 
                                      
   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. 
    
    
8. Normative References 
      
   [ABNF]    Crocker, D. and P. Overell, "Augmented BNF for Syntax 
             Specifications: ABNF", RFC 2234, November 1997. 
    
   [ASN.1]   ITU-T Recommendation X.680 (07/2002) | ISO/IEC 8824-1:2002 
             "Information Technology - Abstract Syntax Notation One 
             (ASN.1): Specification of basic notation" 
    
   [AuthMeth] Harrison, R., "LDAP: Authentication Methods and Connection 
             Level Security Mechanisms", draft-ietf-ldapbis-authmeth-
             xx.txt, (a work in progress). 
    
   [BER]     ITU-T Rec. X.690 (07/2002) | ISO/IEC 8825-1:2002, 
             "Information technology - ASN.1 encoding rules: 
             Specification of Basic Encoding Rules (BER), Canonical 
             Encoding Rules (CER) and Distinguished Encoding Rules 
             (DER)", 2002. 
 
   [IP]      Postel, J., "Internet Protocol", STD5 and RFC 791, 
             September 1981 
    
   [ISO10646] Universal Multiple-Octet Coded Character Set (UCS) - 
             Architecture and Basic Multilingual Plane, ISO/IEC 10646-1 
             : 1993. 
     
   [Keyword] Bradner, S., "Key words for use in RFCs to Indicate 
             Requirement Levels", RFC 2119, March 1997. 
     
   [LDAPDN]  Zeilenga, K., "LDAP: String Representation of 
             Distinguished Names", draft-ietf-ldapbis-dn-xx.txt, (a 
             work in progress). 
    
   [LDAPIANA] Zeilenga, K., "IANA Considerations for LDAP", draft-ietf-
             ldapbis-bcp64-xx.txt, (a work in progress). 
    
   [LDAPURL] Smith, M., "LDAP: Uniform Resource Locator", draft-ietf-
             ldapbis-url-xx.txt, (a work in progress). 
    
   [Models]  Zeilenga, K., "LDAP: Directory Information Models", draft-
             ietf-ldapbis-models-xx.txt (a work in progress). 
    
   [Roadmap] Zeilenga, K., "LDAP: Technical Specification Road Map", 
             draft-ietf-ldapbis-roadmap-xx.txt (a work in progress). 
    
   [SASL]    Melnikov, A., "Simple Authentication and Security Layer", 
             draft-ietf-sasl-rfc2222bis-xx.txt (a work in progress). 
    


  
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   [SASLPrep] Zeilenga, K., "Stringprep profile for user names and 
             passwords", draft-ietf-sasl-saslprep-xx.txt, (a work in 
             progress). 
    
   [StringPrep] Hoffman P. and M. Blanchet, "Preparation of 
             Internationalized Strings ('stringprep')", draft-hoffman-
             rfc3454bis-xx.txt, a work in progress. 
    
   [Syntaxes] Legg, S., and K. Dally, "LDAP: Syntaxes and Matching 
             Rules", draft-ietf-ldapbis-syntaxes-xx.txt, (a work in 
             progress). 
    
   [TCP]     Postel, J., "Transmission Control Protocol", STD7 and RFC 
             793, September 1981 
    
   [TLS]     Dierks, T. and C. Allen. "The TLS Protocol Version 1.1", 
             draft-ietf-tls-rfc2246-bis-xx.txt, a work in progress. 
    
   [Unicode] The Unicode Consortium, "The Unicode Standard, Version 
             3.2.0" is defined by "The Unicode Standard, Version 3.0" 
             (Reading, MA, Addison-Wesley, 2000. ISBN 0-201-61633-5), 
             as amended by the "Unicode Standard Annex #27: Unicode 
             3.1" (http://www.unicode.org/reports/tr27/) and by the 
             "Unicode Standard Annex #28: Unicode 3.2" 
             (http://www.unicode.org/reports/tr28/). 
    
   [URI]     Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 
             Resource Identifiers (URI): Generic Syntax", RFC 2396, 
             August 1998. 
    
   [UTF-8]   Yergeau, F., "UTF-8, a transformation format of ISO 
             10646", STD63 and RFC3629, November 2003. 
    
   [X.500]   ITU-T Rec. X.500, "The Directory: Overview of Concepts, 
             Models and Service", 1993. 
     
   [X.501]   ITU-T Rec. X.501, "The Directory: Models", 1993. 
    
   [X.511]   ITU-T Rec. X.511, "The Directory: Abstract Service 
             Definition", 1993. 
    
    
9. Informative References 
    
   [Glossary] The Unicode Consortium, "Unicode Glossary", 
             <http://www.unicode.org/glossary/>. 
    
   [CharModel]  Whistler, K. and M. Davis, "Unicode Technical Report 
             #17, Character Encoding Model", UTR17, 
             <http://www.unicode.org/unicode/reports/tr17/>, August 
             2000. 
    



  
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   [PROTOS-LDAP] University of Oulu, "PROTOS Test-Suite: c06-ldapv3" 
             <http://www.ee.oulu.fi/research/ouspg/protos/testing/c06/l
             dapv3/> 
    
   [PortReg] IANA, "Port Numbers", 
             http://www.iana.org/assignments/port-numbers 
 
 
10. IANA Considerations 
    
   It is requested that the Internet Assigned Numbers Authority (IANA) 
   update the LDAP result code registry to indicate that this document 
   provides the definitive technical specification for result codes 0-
   36, 48-54, 64-70, 80-90. 
    
   It is requested that the IANA update the LDAP Protocol Mechanism 
   registry to indicate that this document and [AuthMeth] provides the 
   definitive technical specification for the StartTLS 
   (1.3.6.1.4.1.1466.20037) extended operation. 
    
   It is requested that the IANA update the occurrence of "RFC XXXX" in 
   Appendix B with this RFC number at publication. 
 
 
11. Editor's Address 
    
   Jim Sermersheim 
   Novell, Inc. 
   1800 South Novell Place 
   Provo, Utah 84606, USA 
   jimse@novell.com 
   +1 801 861-3088 























  
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Appendix A - LDAP Result Codes 
 
   This normative appendix details additional considerations regarding 
   LDAP result codes and provides a brief, general description of each 
   LDAP result code enumerated in Section 4.1.9. 
    
   Additional result codes MAY be defined for use with extensions 
   [LDAPIANA]. Client implementations SHALL treat any result code which 
   they do not recognize as an unknown error condition. 
    
    
A.1 Non-Error Result Codes 
    
   These result codes (called "non-error" result codes) do not indicate 
   an error condition: 
        success (0), 
        compareFalse (5), 
        compareTrue (6), 
        referral (10), and 
        saslBindInProgress (14). 
    
   The success, compareTrue, and compareFalse result codes indicate 
   successful completion (and, hence, are referred to as "successful" 
   result codes). 
    
   The referral and saslBindInProgress result codes indicate the client 
   is required to take additional action to complete the operation. 
    
    
A.2 Result Codes 
    
   Existing LDAP result codes are described as follows: 
 
        success (0) 
           Indicates the successful completion of an operation. Note: 
           this code is not used with the compare operation. See 
           compareFalse (5) and compareTrue (6).        
    
        operationsError (1) 
           Indicates that the operation is not properly sequenced with 
           relation to other operations (of same or different type). 
 
           For example, this code is returned if the client attempts to 
           StartTLS [TLS] while there are other uncompleted operations 
           or if a TLS layer was already installed. 
 
        protocolError (2) 
           Indicates the server received data which is not well-formed. 
            
           For bind operation only, this code is also used to indicate 
           that the server does not support the requested protocol 
           version. 
            


  
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           For extended operations only, this code indicates that the 
           server does not support (by design or configuration) the 
           extended operation associated with the requestName. 
            
           For request operations specifying multiple controls, this may 
           be used to indicate that the server cannot ignore the order 
           of the controls as specified, or that the combination of the 
           specified controls is invalid or unspecified. 
            
        timeLimitExceeded (3) 
           Indicates that the time limit specified by the client was 
           exceeded before the operation could be completed. 
 
        sizeLimitExceeded (4) 
           Indicates that the size limit specified by the client was 
           exceeded before the operation could be completed. 
         
        compareFalse (5) 
           Indicates that the compare operation has successfully 
           completed and the assertion has evaluated to FALSE or 
           Undefined. 
         
        compareTrue (6) 
           Indicates that the compare operation has successfully 
           completed and the assertion has evaluated to TRUE. 
         
        authMethodNotSupported (7) 
           Indicates that the authentication method or mechanism is not 
           supported. 
         
        strongAuthRequired (8) 
           Indicates that the server has detected that an established 
           security association between the client and server has 
           unexpectedly failed or been compromised, or that the server 
           now requires the client to authenticate using a strong(er) 
           mechanism. 
         
        referral (10) 
           Indicates that a referral needs to be chased to complete the 
           operation (see Section 4.1.10). 
         
        adminLimitExceeded (11) 
           Indicates that an administrative limit has been exceeded. 
         
        unavailableCriticalExtension (12) 
           Indicates a critical control is unrecognized (see Section 
           4.1.11). 
         
        confidentialityRequired (13) 
           Indicates that data confidentiality protections are required. 
         
        saslBindInProgress (14) 



  
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           Indicates the server requires the client to send a new bind 
           request, with the same SASL mechanism, to continue the 
           authentication process (see Section 4.2). 
         
        noSuchAttribute (16) 
           Indicates that the named entry does not contain the specified 
           attribute or attribute value. 
         
        undefinedAttributeType (17) 
           Indicates that a request field contains an unrecognized 
           attribute description. 
         
        inappropriateMatching (18) 
           Indicates that an attempt was made (e.g. in an assertion) to 
           use a matching rule not defined for the attribute type 
           concerned. 
         
        constraintViolation (19) 
           Indicates that the client supplied an attribute value which 
           does not conform to the constraints placed upon it by the 
           data model. 
         
           For example, this code is returned when multiple values are 
           supplied to an attribute which has a SINGLE-VALUE constraint. 
         
        attributeOrValueExists (20) 
           Indicates that the client supplied an attribute or value to 
           be added to an entry, but the attribute or value already 
           exists. 
         
        invalidAttributeSyntax (21) 
           Indicates that a purported attribute value does not conform 
           to the syntax of the attribute. 
         
        noSuchObject (32) 
           Indicates that the object does not exist in the DIT. 
         
        aliasProblem (33) 
           Indicates that an alias problem has occurred. For example, 
           the code may used to indicate an alias has been dereferenced 
           which names no object. 
         
        invalidDNSyntax (34) 
           Indicates that an LDAPDN or RelativeLDAPDN field (e.g. search 
           base, target entry, ModifyDN newrdn, etc.) of a request does 
           not conform to the required syntax or contains attribute 
           values which do not conform to the syntax of the attribute's 
           type. 
         
        aliasDereferencingProblem (36) 
           Indicates that a problem occurred while dereferencing an 
           alias. Typically an alias was encountered in a situation 
           where it was not allowed or where access was denied. 
         
  
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        inappropriateAuthentication (48) 
           Indicates the server requires the client which had attempted 
           to bind anonymously or without supplying credentials to 
           provide some form of credentials. 
         
        invalidCredentials (49) 
           Indicates that the provided credentials (e.g. the user's name 
           and password) are invalid. 
         
        insufficientAccessRights (50) 
           Indicates that the client does not have sufficient access 
           rights to perform the operation. 
         
        busy (51) 
           Indicates that the server is too busy to service the 
           operation. 
         
        unavailable (52) 
           Indicates that the server is shutting down or a subsystem 
           necessary to complete the operation is offline. 
         
        unwillingToPerform (53) 
           Indicates that the server is unwilling to perform the 
           operation. 
         
        loopDetect (54) 
           Indicates that the server has detected an internal loop (e.g. 
           while dereferencing aliases or chaining an operation). 
         
        namingViolation (64) 
           Indicates that the entry's name violates naming restrictions. 
         
        objectClassViolation (65) 
           Indicates that the entry violates object class restrictions. 
         
        notAllowedOnNonLeaf (66) 
           Indicates that the operation is inappropriately acting upon a 
           non-leaf entry. 
         
        notAllowedOnRDN (67) 
           Indicates that the operation is inappropriately attempting to 
           remove a value which forms the entry's relative distinguished 
           name. 
         
        entryAlreadyExists (68) 
           Indicates that the request cannot be fulfilled (added, moved, 
           or renamed) as the target entry already exists. 
         
        objectClassModsProhibited (69) 
           Indicates that an attempt to modify the object class(es) of 
           an entry's 'objectClass' attribute is prohibited. 
         
           For example, this code is returned when a client attempts to 
           modify the structural object class of an entry. 
  
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        affectsMultipleDSAs (71) 
           Indicates that the operation cannot be performed as it would 
           affect multiple servers (DSAs). 
         
        other (80) 
           Indicates the server has encountered an internal error. 
















































  
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              Lightweight Directory Access Protocol Version 3 
                                      
Appendix B - Complete ASN.1 Definition 
    
        This appendix is normative. 
    
        Lightweight-Directory-Access-Protocol-V3  
        -- Copyright (C) The Internet Society (2004). This version of 
        -- this ASN.1 module is part of RFC XXXX; see the RFC itself 
        -- for full legal notices. 
        DEFINITIONS 
        IMPLICIT TAGS 
        EXTENSIBILITY IMPLIED ::= 
    
        BEGIN 
    
        LDAPMessage ::= SEQUENCE { 
             messageID       MessageID, 
             protocolOp      CHOICE { 
                  bindRequest           BindRequest, 
                  bindResponse          BindResponse, 
                  unbindRequest         UnbindRequest, 
                  searchRequest         SearchRequest, 
                  searchResEntry        SearchResultEntry, 
                  searchResDone         SearchResultDone, 
                  searchResRef          SearchResultReference, 
                  modifyRequest         ModifyRequest, 
                  modifyResponse        ModifyResponse, 
                  addRequest            AddRequest, 
                  addResponse           AddResponse, 
                  delRequest            DelRequest, 
                  delResponse           DelResponse, 
                  modDNRequest          ModifyDNRequest, 
                  modDNResponse         ModifyDNResponse, 
                  compareRequest        CompareRequest, 
                  compareResponse       CompareResponse, 
                  abandonRequest        AbandonRequest, 
                  extendedReq           ExtendedRequest, 
                  extendedResp          ExtendedResponse, 
                  ..., 
                  intermediateResponse  IntermediateResponse }, 
             controls       [0] Controls OPTIONAL } 
    
        MessageID ::= INTEGER (0 .. maxInt) 
    
        maxInt INTEGER ::= 2147483647 -- (2^^31 - 1) -- 
    
        LDAPString ::= OCTET STRING -- UTF-8 encoded, 
                                    -- [ISO10646] characters 
    
        LDAPOID ::= OCTET STRING -- Constrained to <numericoid> [Models] 
    
        LDAPDN ::= LDAPString -- Constrained to <distinguishedName> 
                              -- [LDAPDN] 
    
        RelativeLDAPDN ::= LDAPString -- Constrained to <name-component> 
  
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                                      -- [LDAPDN] 
    
        AttributeDescription ::= LDAPString 
                                -- Constrained to <attributedescription> 
                                -- [Models] 
    
        AttributeValue ::= OCTET STRING 
    
        AttributeValueAssertion ::= SEQUENCE { 
             attributeDesc   AttributeDescription, 
             assertionValue  AssertionValue } 
    
        AssertionValue ::= OCTET STRING 
    
        PartialAttribute ::= SEQUENCE { 
             type       AttributeDescription, 
             vals       SET OF value AttributeValue } 
    
        Attribute ::= PartialAttribute(WITH COMPONENTS { 
             ...,  
             vals (SIZE(1..MAX))}) 
    
        MatchingRuleId ::= LDAPString 
    
        LDAPResult ::= SEQUENCE { 
             resultCode         ENUMERATED { 
                  success                      (0), 
                  operationsError              (1), 
                  protocolError                (2), 
                  timeLimitExceeded            (3), 
                  sizeLimitExceeded            (4), 
                  compareFalse                 (5), 
                  compareTrue                  (6), 
                  authMethodNotSupported       (7), 
                  strongAuthRequired           (8), 
                       -- 9 reserved -- 
                  referral                     (10), 
                  adminLimitExceeded           (11), 
                  unavailableCriticalExtension (12), 
                  confidentialityRequired      (13), 
                  saslBindInProgress           (14), 
                  noSuchAttribute              (16), 
                  undefinedAttributeType       (17), 
                  inappropriateMatching        (18), 
                  constraintViolation          (19), 
                  attributeOrValueExists       (20), 
                  invalidAttributeSyntax       (21), 
                       -- 22-31 unused -- 
                  noSuchObject                 (32), 
                  aliasProblem                 (33), 
                  invalidDNSyntax              (34), 
                       -- 35 reserved for undefined isLeaf -- 
                  aliasDereferencingProblem    (36), 
                       -- 37-47 unused -- 
  
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                  inappropriateAuthentication  (48), 
                  invalidCredentials           (49), 
                  insufficientAccessRights     (50), 
                  busy                         (51), 
                  unavailable                  (52), 
                  unwillingToPerform           (53), 
                  loopDetect                   (54), 
                       -- 55-63 unused -- 
                  namingViolation              (64), 
                  objectClassViolation         (65), 
                  notAllowedOnNonLeaf          (66), 
                  notAllowedOnRDN              (67), 
                  entryAlreadyExists           (68), 
                  objectClassModsProhibited    (69), 
                       -- 70 reserved for CLDAP -- 
                  affectsMultipleDSAs          (71), 
                       -- 72-79 unused -- 
                  other                        (80), 
                  ... }, 
             matchedDN          LDAPDN, 
             diagnosticMessage  LDAPString, 
             referral           [3] Referral OPTIONAL } 
    
        Referral ::= SEQUENCE SIZE (1..MAX) OF uri URI 
    
        URI ::= LDAPString     -- limited to characters permitted in 
                               -- URIs 
    
        Controls ::= SEQUENCE OF control Control 
    
        Control ::= SEQUENCE { 
             controlType             LDAPOID, 
             criticality             BOOLEAN DEFAULT FALSE, 
             controlValue            OCTET STRING OPTIONAL } 
    
        BindRequest ::= [APPLICATION 0] SEQUENCE { 
             version                 INTEGER (1 .. 127), 
             name                    LDAPDN, 
             authentication          AuthenticationChoice } 
    
        AuthenticationChoice ::= CHOICE { 
             simple                  [0] OCTET STRING, 
                                     -- 1 and 2 reserved 
             sasl                    [3] SaslCredentials, 
             ... } 
    
        SaslCredentials ::= SEQUENCE { 
             mechanism               LDAPString, 
             credentials             OCTET STRING OPTIONAL } 
    
        BindResponse ::= [APPLICATION 1] SEQUENCE { 
             COMPONENTS OF LDAPResult, 
             serverSaslCreds    [7] OCTET STRING OPTIONAL } 
    
  
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        UnbindRequest ::= [APPLICATION 2] NULL 
    
        SearchRequest ::= [APPLICATION 3] SEQUENCE { 
             baseObject      LDAPDN, 
             scope           ENUMERATED { 
                  baseObject              (0), 
                  singleLevel             (1), 
                  wholeSubtree            (2) }, 
             derefAliases    ENUMERATED { 
                  neverDerefAliases       (0), 
                  derefInSearching        (1), 
                  derefFindingBaseObj     (2), 
                  derefAlways             (3) }, 
             sizeLimit       INTEGER (0 .. maxInt), 
             timeLimit       INTEGER (0 .. maxInt), 
             typesOnly       BOOLEAN, 
             filter          Filter, 
             attributes      AttributeSelection } 
    
        AttributeSelection ::= SEQUENCE OF selector LDAPString 
                       -- The LDAPString is constrained to 
                       -- <attributeSelection> in Section 4.5.1 
    
        Filter ::= CHOICE { 
             and             [0] SET OF filter Filter, 
             or              [1] SET OF filter Filter, 
             not             [2] Filter, 
             equalityMatch   [3] AttributeValueAssertion, 
             substrings      [4] SubstringFilter, 
             greaterOrEqual  [5] AttributeValueAssertion, 
             lessOrEqual     [6] AttributeValueAssertion, 
             present         [7] AttributeDescription, 
             approxMatch     [8] AttributeValueAssertion, 
             extensibleMatch [9] MatchingRuleAssertion } 
    
        SubstringFilter ::= SEQUENCE { 
             type           AttributeDescription, 
             -- at least one must be present, 
             -- initial and final can occur at most once 
             substrings     SEQUENCE SIZE (1..MAX) OF substring CHOICE { 
                  initial [0] AssertionValue, 
                  any     [1] AssertionValue, 
                  final   [2] AssertionValue } } 
    
        MatchingRuleAssertion ::= SEQUENCE { 
             matchingRule    [1] MatchingRuleId OPTIONAL, 
             type            [2] AttributeDescription OPTIONAL, 
             matchValue      [3] AssertionValue, 
             dnAttributes    [4] BOOLEAN DEFAULT FALSE } 
    
        SearchResultEntry ::= [APPLICATION 4] SEQUENCE { 
             objectName      LDAPDN, 
             attributes      PartialAttributeList } 
    
  
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        PartialAttributeList ::= SEQUENCE OF  
                             partialAttribute PartialAttribute   
    
        SearchResultReference ::= [APPLICATION 19] SEQUENCE  
                                  SIZE (1..MAX) OF uri URI 
    
        SearchResultDone ::= [APPLICATION 5] LDAPResult 
    
        ModifyRequest ::= [APPLICATION 6] SEQUENCE { 
             object          LDAPDN, 
             changes         SEQUENCE OF change SEQUENCE { 
                  operation       ENUMERATED { 
                       add     (0), 
                       delete  (1), 
                       replace (2) }, 
                  modification    PartialAttribute } } 
    
        ModifyResponse ::= [APPLICATION 7] LDAPResult 
    
        AddRequest ::= [APPLICATION 8] SEQUENCE { 
             entry           LDAPDN, 
             attributes      AttributeList } 
    
        AttributeList ::= SEQUENCE OF attribute Attribute 
    
        AddResponse ::= [APPLICATION 9] LDAPResult 
    
        DelRequest ::= [APPLICATION 10] LDAPDN 
    
        DelResponse ::= [APPLICATION 11] LDAPResult 
    
        ModifyDNRequest ::= [APPLICATION 12] SEQUENCE { 
             entry           LDAPDN, 
             newrdn          RelativeLDAPDN, 
             deleteoldrdn    BOOLEAN, 
             newSuperior     [0] LDAPDN OPTIONAL } 
    
        ModifyDNResponse ::= [APPLICATION 13] LDAPResult 
    
        CompareRequest ::= [APPLICATION 14] SEQUENCE { 
             entry           LDAPDN, 
             ava             AttributeValueAssertion } 
    
        CompareResponse ::= [APPLICATION 15] LDAPResult 
    
        AbandonRequest ::= [APPLICATION 16] MessageID 
    
        ExtendedRequest ::= [APPLICATION 23] SEQUENCE { 
             requestName      [0] LDAPOID, 
             requestValue     [1] OCTET STRING OPTIONAL } 
    
        ExtendedResponse ::= [APPLICATION 24] SEQUENCE { 
             COMPONENTS OF LDAPResult, 
             responseName     [10] LDAPOID OPTIONAL, 
  
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             responseValue    [11] OCTET STRING OPTIONAL } 
    
        IntermediateResponse ::= [APPLICATION 25] SEQUENCE { 
             responseName     [0] LDAPOID OPTIONAL, 
             responseValue    [1] OCTET STRING OPTIONAL } 
    
        END 
















































  
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Appendix C - Changes 
 
   This appendix is non-normative. 
    
   This appendix summarizes substantive changes made to RFC 2251 and RFC 
   2830. 
    
    
C.1 Changes made to RFC 2251: 
    
   This section summarizes the substantive changes made to Sections 1, 
   2, 3.1, and 4 through the remainder of RFC 2251. Readers should 
   consult [Models] and [AuthMeth] for summaries of changes to other 
   sections. 
    
    
C.1.1 Section 1 
    
   - Removed IESG note. Post publication of RFC 2251, mandatory LDAP 
     authentication mechanisms have been standardized which are 
     sufficient to remove this note. See [AuthMeth] for authentication 
     mechanisms. 
    
    
C.1.2 Section 3.1 and others 
 
   - Removed notes giving history between LDAP v1, v2 and v3. Instead, 
     added sufficient language so that this document can stand on its 
     own. 
    
    
C.1.3 Section 4 
 
   - Clarified where the extensibility features of ASN.1 apply to the 
     protocol. This change also affected various ASN.1 types. 
   - Removed the requirement that servers which implement version 3 or 
     later MUST provide the 'supportedLDAPVersion' attribute. This 
     statement provided no interoperability advantages. 
 
 
C.1.4 Section 4.1.1 
 
   - There was a mandatory requirement for the server to return a 
     Notice of Disconnection and drop the connection when a PDU is 
     malformed in a certain way. This has been clarified such that the 
     server SHOULD return the Notice of Disconnection, and MUST drop 
     the connection. 
 
 
C.1.5 Section 4.1.1.1 
 
   - Clarified that the messageID of requests MUST be non-zero. 



  
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   - Clarified when it is and isn't appropriate to return an already 
     used message id. RFC 2251 accidentally imposed synchronous server 
     behavior in its wording of this. 
 
 
C.1.6 Section 4.1.2 
 
   - Stated that LDAPOID is constrained to <numericoid> from [Models]. 
 
 
C.1.7 Section 4.1.5.1 and others 
 
   - 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 
 
   - Combined the definitions of PartialAttribute and Attribute here, 
     and defined Attribute in terms of PartialAttribute. 
 
 
C.1.9 Section 4.1.10 
 
   - Renamed "errorMessage" to "diagnosticMessage" as it is allowed to 
     be sent for non-error results. 
   - Moved some language into Appendix A, and refer the reader there. 
   - Allowed matchedDN to be present for other result codes than those 
     listed in RFC 2251. 
 
 
C.1.10 Section 4.1.11 
 
   - Defined referrals in terms of URIs rather than URLs. 
   - Removed the requirement that all referral URIs MUST be equally 
     capable of progressing the operation. The statement was ambiguous 
     and provided no instructions on how to carry it out. 
   - Added the requirement that clients MUST NOT loop between servers. 
   - Clarified the instructions for using LDAPURLs in referrals, and in 
     doing so added a recommendation that the scope part be present. 
 
 
C.1.11 Section 4.1.12 
 
   - Specified how control values defined in terms of ASN.1 are to be 
     encoded. 
   - Noted that the criticality field is only applied to request 
     messages (except unbindRequest), and must be ignored when present 
     on response messages and unbindRequest. 
   - Added language regarding combinations of controls and the ordering 
     of controls on a message. 


  
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   - Specified that when the semantics of the combination of controls 
     is undefined or unknown, it results in a protocolError. 
   - Changed "The server MUST be prepared" to "Implementations MUST be 
     prepared" in the eighth paragraph to reflect that both client and 
     server implementations must be able to handle this (as both parse 
     controls). 
 
 
C.1.12 Section 4.2 
 
   - Mandated that servers return protocolError when the version is not 
     supported. 
   - Clarified behavior when the simple authentication is used, the 
     name is empty and the password is non-empty. 
   - Required servers to not dereference aliases for bind. This was 
     added for consistency with other operations and to help ensure 
     data consistency. 
   - Required that textual passwords be transferred as UTF-8 encoded 
     Unicode, and added recommendations on string preparation. This was 
     to help ensure interoperability of passwords being sent from 
     different clients. 
 
 
C.1.13 Section 4.2.1 
 
   - This section was largely reorganized for readability and language 
     was added to clarify the authentication state of failed and 
     abandoned bind operations. 
   - Removed: "If a SASL transfer encryption or integrity mechanism has 
     been negotiated, that mechanism does not support the changing of 
     credentials from one identity to another, then the client MUST 
     instead establish a new connection." 
     Each SASL negotiation is, generally, independent of other SASL 
     negotiations. If there were dependencies between multiple 
     negotiations of a particular mechanism, the mechanism technical 
     specification should detail how applications are to deal with 
     them. LDAP should not require any special handling. And if an LDAP 
     client had used such a mechanism, it would have the option of 
     using another mechanism. 
   - Dropped MUST imperative in paragraph 3 to align with [Keywords]. 
   - Mandated that clients not send non-bind operations while a bind is 
     in progress, and suggested that servers not process them if they 
     are received. This is needed to ensure proper sequencing of the 
     bind in relationship to other operations. 
    
    
C.1.14 Section 4.2.3 
 
   - Moved most error-related text to Appendix A, and added text 
     regarding certain errors used in conjunction with the bind 
     operation. 
   - Prohibited the server from specifying serverSaslCreds when not 
     appropriate. 
    
  
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C.1.15 Section 4.3 
 
   - Required both peers to cease transmission and close the LDAP 
     exchange for the unbind operation. 
    
    
C.1.16 Section 4.4 
 
   - Added instructions for future specifications of Unsolicited 
     Notifications. 
    
    
C.1.17 Section 4.5.1 
 
   - SearchRequest attributes is now defined as an AttributeSelection 
     type rather than AttributeDescriptionList, and an ABNF is 
     provided. 
   - SearchRequest attributes may contain duplicate attribute 
     descriptions. This was previously prohibited. Now servers are 
     instructed to ignore subsequent names when they are duplicated. 
     This was relaxed in order to allow different short names and also 
     OIDs to be requested for an attribute. 
   - The Filter 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. 
   - Clarified the semantics of the derefAliases choices. 
   - Added instructions for equalityMatch, substrings, greaterOrEqual, 
     lessOrEqual, and approxMatch. 
    
    
C.1.18 Section 4.5.2 
 
   - Recommended that servers not use attribute short names when it 
     knows they are ambiguous or may cause interoperability problems. 
   - Removed all mention of ExtendedResponse due to lack of 
     implementation. 
    
    
C.1.19 Section 4.5.3 
 
   - Made changes similar to those made to Section 4.1.11. 
    
    
C.1.20 Section 4.5.3.1 
 
   - Fixed examples to adhere to changes made to Section 4.5.3. 
    
    
C.1.21 Section 4.6 
 
  
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   - Removed restriction that required an EQUALITY matching rule in 
     order to perform value delete modifications. It is sufficiently 
     documented that in absence of an equality matching rule, octet 
     equality is used. 
   - Replaced AttributeTypeAndValues with Attribute as they are 
     equivalent. 
   - Clarified what type of modification changes might temporarily 
     violate schema. 
    
    
C.1.22 Section 4.7 
 
   - Aligned Add operation with X.511 in that the attributes of the RDN 
     are used in conjunction with the listed attributes to create the 
     entry. Previously, Add required that the distinguished values be 
     present in the listed attributes. 
    
    
C.1.23 Section 4.9 
 
   - Required servers to not dereference aliases for modify DN. This 
     was added for consistency with other operations and to help ensure 
     data consistency. 
   - Allow modify DN to fail when moving between naming contexts. 
   - Specified what happens when the attributes of the newrdn are no 
     present on the entry. 
 
 
C.1.24 Section 4.10 
 
   - Clarified that compareFalse means that the compare took place and 
     the result is false. There was confusion which lead people to 
     believe that an Undefined match resulted in compareFalse. 
   - Required servers to not dereference aliases for compare. This was 
     added for consistency with other operations and to help ensure 
     data consistency. 
    
    
C.1.25 Section 4.11 
 
   - Explained that since abandon returns no response, clients should 
     not use it if they need to know the outcome. 
   - Specified that Abandon and Unbind cannot be abandoned.  
    
 
C.1.26 Section 4.12 
 
   - Specified how values of extended operations defined in terms of 
     ASN.1 are to be encoded. 
   - Added instructions on what extended operation specifications 
     consist of. 
   - Added a recommendation that servers advertise supported extended 
     operations. 
 
  
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C.1.27 Section 5.2 
 
   - Moved referral-specific instructions into referral-related 
     sections. 
 
 
C.1.28 Section 7 
 
   - Reworded notes regarding SASL not protecting certain aspects of 
     the LDAP bind PDU. 
   - Noted that Servers are encouraged to prevent directory 
     modifications by clients that have authenticated anonymously 
     [AuthMeth].  
   - Added a note regarding the scenario where an identity is changed 
     (deleted, privileges or credentials modified, etc.). 
   - Warned against following referrals that may have been injected in 
     the data stream. 
   - Noted that servers should protect information equally, whether in 
     an error condition or not, and mentioned specifically; matchedDN, 
     diagnosticMessage, and resultCodes.  
   - Added a note regarding malformed and long encodings. 
 
 
C.1.29 Appendix A 
 
   - Added "EXTENSIBILITY IMPLIED" to ASN.1 definition. 
   - Removed AttributeType. It is not used. 
 
 
C.2 Changes made to RFC 2830: 
    
   This section summarizes the substantive changes made to Sections of 
   RFC 2830. Readers should consult [AuthMeth] for summaries of changes 
   to other sections. 
    
    
C.2.1 Section 2.3 
 
   - Removed wording indicating that referrals can be returned from 
     StartTLS 
   - Removed requirement that only a narrow set of result codes can be 
     returned. Some result codes are required in certain scenarios, but 
     any other may be returned if appropriate. 
    
    
C.2.1 Section 4.13.3.1 
    
   - Reworded most of this section and added the requirement that after 
     the TLS connection has been closed, the server MUST NOT send 
     responses to any request message received before the TLS closure. 
    
 
C.3 Changes made to RFC 3771: 
  
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   - In general, all technical language was transferred in whole. 
     Supporting and background language seen as redundant due to its 
     presence in this document was omitted. 
 


















































  
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