7 Network Working Group M. Wahl
8 Request for Comments: 2251 Critical Angle Inc.
9 Category: Standards Track T. Howes
10 Netscape Communications Corp.
16 Lightweight Directory Access Protocol (v3)
18 1. Status of this Memo
20 This document specifies an Internet standards track protocol for the
21 Internet community, and requests discussion and suggestions for
22 improvements. Please refer to the current edition of the "Internet
23 Official Protocol Standards" (STD 1) for the standardization state
24 and status of this protocol. Distribution of this memo is unlimited.
28 Copyright (C) The Internet Society (1997). All Rights Reserved.
32 This document describes a directory access protocol that provides
33 both read and update access. Update access requires secure
34 authentication, but this document does not mandate implementation of
35 any satisfactory authentication mechanisms.
37 In accordance with RFC 2026, section 4.4.1, this specification is
38 being approved by IESG as a Proposed Standard despite this
39 limitation, for the following reasons:
41 a. to encourage implementation and interoperability testing of
42 these protocols (with or without update access) before they
45 b. to encourage deployment and use of these protocols in read-only
46 applications. (e.g. applications where LDAPv3 is used as
47 a query language for directories which are updated by some
48 secure mechanism other than LDAP), and
50 c. to avoid delaying the advancement and deployment of other Internet
51 standards-track protocols which require the ability to query, but
52 not update, LDAPv3 directory servers.
58 Wahl, et. al. Standards Track [Page 1]
60 RFC 2251 LDAPv3 December 1997
63 Readers are hereby warned that until mandatory authentication
64 mechanisms are standardized, clients and servers written according to
65 this specification which make use of update functionality are
66 UNLIKELY TO INTEROPERATE, or MAY INTEROPERATE ONLY IF AUTHENTICATION
67 IS REDUCED TO AN UNACCEPTABLY WEAK LEVEL.
69 Implementors are hereby discouraged from deploying LDAPv3 clients or
70 servers which implement the update functionality, until a Proposed
71 Standard for mandatory authentication in LDAPv3 has been approved and
76 1. Status of this Memo .................................... 1
77 Copyright Notice ....................................... 1
78 IESG Note .............................................. 1
79 2. Abstract ............................................... 3
80 3. Models ................................................. 4
81 3.1. Protocol Model ........................................ 4
82 3.2. Data Model ............................................ 5
83 3.2.1. Attributes of Entries ............................... 5
84 3.2.2. Subschema Entries and Subentries .................... 7
85 3.3. Relationship to X.500 ................................. 8
86 3.4. Server-specific Data Requirements ..................... 8
87 4. Elements of Protocol ................................... 9
88 4.1. Common Elements ....................................... 9
89 4.1.1. Message Envelope .................................... 9
90 4.1.1.1. Message ID ........................................ 11
91 4.1.2. String Types ........................................ 11
92 4.1.3. Distinguished Name and Relative Distinguished Name .. 11
93 4.1.4. Attribute Type ...................................... 12
94 4.1.5. Attribute Description ............................... 13
95 4.1.5.1. Binary Option ..................................... 14
96 4.1.6. Attribute Value ..................................... 14
97 4.1.7. Attribute Value Assertion ........................... 15
98 4.1.8. Attribute ........................................... 15
99 4.1.9. Matching Rule Identifier ............................ 15
100 4.1.10. Result Message ..................................... 16
101 4.1.11. Referral ........................................... 18
102 4.1.12. Controls ........................................... 19
103 4.2. Bind Operation ........................................ 20
104 4.2.1. Sequencing of the Bind Request ...................... 21
105 4.2.2. Authentication and Other Security Services .......... 22
106 4.2.3. Bind Response ....................................... 23
107 4.3. Unbind Operation ...................................... 24
108 4.4. Unsolicited Notification .............................. 24
109 4.4.1. Notice of Disconnection ............................. 24
110 4.5. Search Operation ...................................... 25
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116 RFC 2251 LDAPv3 December 1997
119 4.5.1. Search Request ...................................... 25
120 4.5.2. Search Result ....................................... 29
121 4.5.3. Continuation References in the Search Result ........ 31
122 4.5.3.1. Example ........................................... 31
123 4.6. Modify Operation ...................................... 32
124 4.7. Add Operation ......................................... 34
125 4.8. Delete Operation ...................................... 35
126 4.9. Modify DN Operation ................................... 36
127 4.10. Compare Operation .................................... 37
128 4.11. Abandon Operation .................................... 38
129 4.12. Extended Operation ................................... 38
130 5. Protocol Element Encodings and Transfer ................ 39
131 5.1. Mapping Onto BER-based Transport Services ............. 39
132 5.2. Transfer Protocols .................................... 40
133 5.2.1. Transmission Control Protocol (TCP) ................. 40
134 6. Implementation Guidelines .............................. 40
135 6.1. Server Implementations ................................ 40
136 6.2. Client Implementations ................................ 40
137 7. Security Considerations ................................ 41
138 8. Acknowledgements ....................................... 41
139 9. Bibliography ........................................... 41
140 10. Authors' Addresses ..................................... 42
141 Appendix A - Complete ASN.1 Definition ..................... 44
142 Full Copyright Statement ................................... 50
146 The protocol described in this document is designed to provide access
147 to directories supporting the X.500 models, while not incurring the
148 resource requirements of the X.500 Directory Access Protocol (DAP).
149 This protocol is specifically targeted at management applications and
150 browser applications that provide read/write interactive access to
151 directories. When used with a directory supporting the X.500
152 protocols, it is intended to be a complement to the X.500 DAP.
154 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
155 "SHOULD", "SHOULD NOT", "RECOMMENDED", and "MAY" in this document
156 are to be interpreted as described in RFC 2119 [10].
158 Key aspects of this version of LDAP are:
160 - All protocol elements of LDAPv2 (RFC 1777) are supported. The
161 protocol is carried directly over TCP or other transport, bypassing
162 much of the session/presentation overhead of X.500 DAP.
164 - Most protocol data elements can be encoded as ordinary strings
165 (e.g., Distinguished Names).
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172 RFC 2251 LDAPv3 December 1997
175 - Referrals to other servers may be returned.
177 - SASL mechanisms may be used with LDAP to provide association
180 - Attribute values and Distinguished Names have been
181 internationalized through the use of the ISO 10646 character set.
183 - The protocol can be extended to support new operations, and
184 controls may be used to extend existing operations.
186 - Schema is published in the directory for use by clients.
190 Interest in X.500 [1] directory technologies in the Internet has led
191 to efforts to reduce the high cost of entry associated with use of
192 these technologies. This document continues the efforts to define
193 directory protocol alternatives, updating the LDAP [2] protocol
198 The general model adopted by this protocol is one of clients
199 performing protocol operations against servers. In this model, a
200 client transmits a protocol request describing the operation to be
201 performed to a server. The server is then responsible for performing
202 the necessary operation(s) in the directory. Upon completion of the
203 operation(s), the server returns a response containing any results or
204 errors to the requesting client.
206 In keeping with the goal of easing the costs associated with use of
207 the directory, it is an objective of this protocol to minimize the
208 complexity of clients so as to facilitate widespread deployment of
209 applications capable of using the directory.
211 Note that although servers are required to return responses whenever
212 such responses are defined in the protocol, there is no requirement
213 for synchronous behavior on the part of either clients or servers.
214 Requests and responses for multiple operations may be exchanged
215 between a client and server in any order, provided the client
216 eventually receives a response for every request that requires one.
218 In LDAP versions 1 and 2, no provision was made for protocol servers
219 returning referrals to clients. However, for improved performance
220 and distribution this version of the protocol permits servers to
221 return to clients referrals to other servers. This allows servers to
222 offload the work of contacting other servers to progress operations.
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228 RFC 2251 LDAPv3 December 1997
231 Note that the core protocol operations defined in this document can
232 be mapped to a strict subset of the X.500(1997) directory abstract
233 service, so it can be cleanly provided by the DAP. However there is
234 not a one-to-one mapping between LDAP protocol operations and DAP
235 operations: server implementations acting as a gateway to X.500
236 directories may need to make multiple DAP requests.
240 This section provides a brief introduction to the X.500 data model,
243 The LDAP protocol assumes there are one or more servers which jointly
244 provide access to a Directory Information Tree (DIT). The tree is
245 made up of entries. Entries have names: one or more attribute values
246 from the entry form its relative distinguished name (RDN), which MUST
247 be unique among all its siblings. The concatenation of the relative
248 distinguished names of the sequence of entries from a particular
249 entry to an immediate subordinate of the root of the tree forms that
250 entry's Distinguished Name (DN), which is unique in the tree. An
251 example of a Distinguished Name is
253 CN=Steve Kille, O=Isode Limited, C=GB
255 Some servers may hold cache or shadow copies of entries, which can be
256 used to answer search and comparison queries, but will return
257 referrals or contact other servers if modification operations are
260 Servers which perform caching or shadowing MUST ensure that they do
261 not violate any access control constraints placed on the data by the
264 The largest collection of entries, starting at an entry that is
265 mastered by a particular server, and including all its subordinates
266 and their subordinates, down to the entries which are mastered by
267 different servers, is termed a naming context. The root of the DIT
268 is a DSA-specific Entry (DSE) and not part of any naming context:
269 each server has different attribute values in the root DSE. (DSA is
270 an X.500 term for the directory server).
272 3.2.1. Attributes of Entries
274 Entries consist of a set of attributes. An attribute is a type with
275 one or more associated values. The attribute type is identified by a
276 short descriptive name and an OID (object identifier). The attribute
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284 RFC 2251 LDAPv3 December 1997
287 type governs whether there can be more than one value of an attribute
288 of that type in an entry, the syntax to which the values must
289 conform, the kinds of matching which can be performed on values of
290 that attribute, and other functions.
292 An example of an attribute is "mail". There may be one or more values
293 of this attribute, they must be IA5 (ASCII) strings, and they are
294 case insensitive (e.g. "foo@bar.com" will match "FOO@BAR.COM").
296 Schema is the collection of attribute type definitions, object class
297 definitions and other information which a server uses to determine
298 how to match a filter or attribute value assertion (in a compare
299 operation) against the attributes of an entry, and whether to permit
300 add and modify operations. The definition of schema for use with
301 LDAP is given in [5] and [6]. Additional schema elements may be
302 defined in other documents.
304 Each entry MUST have an objectClass attribute. The objectClass
305 attribute specifies the object classes of an entry, which along with
306 the system and user schema determine the permitted attributes of an
307 entry. Values of this attribute may be modified by clients, but the
308 objectClass attribute cannot be removed. Servers may restrict the
309 modifications of this attribute to prevent the basic structural class
310 of the entry from being changed (e.g. one cannot change a person into
311 a country). When creating an entry or adding an objectClass value to
312 an entry, all superclasses of the named classes are implicitly added
313 as well if not already present, and the client must supply values for
314 any mandatory attributes of new superclasses.
316 Some attributes, termed operational attributes, are used by servers
317 for administering the directory system itself. They are not returned
318 in search results unless explicitly requested by name. Attributes
319 which are not operational, such as "mail", will have their schema and
320 syntax constraints enforced by servers, but servers will generally
321 not make use of their values.
323 Servers MUST NOT permit clients to add attributes to an entry unless
324 those attributes are permitted by the object class definitions, the
325 schema controlling that entry (specified in the subschema - see
326 below), or are operational attributes known to that server and used
327 for administrative purposes. Note that there is a particular
328 objectClass 'extensibleObject' defined in [5] which permits all user
329 attributes to be present in an entry.
331 Entries MAY contain, among others, the following operational
332 attributes, defined in [5]. These attributes are maintained
333 automatically by the server and are not modifiable by clients:
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340 RFC 2251 LDAPv3 December 1997
343 - creatorsName: the Distinguished Name of the user who added this
344 entry to the directory.
346 - createTimestamp: the time this entry was added to the directory.
348 - modifiersName: the Distinguished Name of the user who last modified
351 - modifyTimestamp: the time this entry was last modified.
353 - subschemaSubentry: the Distinguished Name of the subschema entry
354 (or subentry) which controls the schema for this entry.
356 3.2.2. Subschema Entries and Subentries
358 Subschema entries are used for administering information about the
359 directory schema, in particular the object classes and attribute
360 types supported by directory servers. A single subschema entry
361 contains all schema definitions used by entries in a particular part
362 of the directory tree.
364 Servers which follow X.500(93) models SHOULD implement subschema
365 using the X.500 subschema mechanisms, and so these subschemas are not
366 ordinary entries. LDAP clients SHOULD NOT assume that servers
367 implement any of the other aspects of X.500 subschema. A server
368 which masters entries and permits clients to modify these entries
369 MUST implement and provide access to these subschema entries, so that
370 its clients may discover the attributes and object classes which are
371 permitted to be present. It is strongly recommended that all other
372 servers implement this as well.
374 The following four attributes MUST be present in all subschema
377 - cn: this attribute MUST be used to form the RDN of the subschema
380 - objectClass: the attribute MUST have at least the values "top" and
383 - objectClasses: each value of this attribute specifies an object
384 class known to the server.
386 - attributeTypes: each value of this attribute specifies an attribute
387 type known to the server.
389 These are defined in [5]. Other attributes MAY be present in
390 subschema entries, to reflect additional supported capabilities.
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396 RFC 2251 LDAPv3 December 1997
399 These include matchingRules, matchingRuleUse, dITStructureRules,
400 dITContentRules, nameForms and ldapSyntaxes.
402 Servers SHOULD provide the attributes createTimestamp and
403 modifyTimestamp in subschema entries, in order to allow clients to
404 maintain their caches of schema information.
406 Clients MUST only retrieve attributes from a subschema entry by
407 requesting a base object search of the entry, where the search filter
408 is "(objectClass=subschema)". (This will allow LDAPv3 servers which
409 gateway to X.500(93) to detect that subentry information is being
412 3.3. Relationship to X.500
414 This document defines LDAP in terms of X.500 as an X.500 access
415 mechanism. An LDAP server MUST act in accordance with the
416 X.500(1993) series of ITU recommendations when providing the service.
417 However, it is not required that an LDAP server make use of any X.500
418 protocols in providing this service, e.g. LDAP can be mapped onto any
419 other directory system so long as the X.500 data and service model as
420 used in LDAP is not violated in the LDAP interface.
422 3.4. Server-specific Data Requirements
424 An LDAP server MUST provide information about itself and other
425 information that is specific to each server. This is represented as
426 a group of attributes located in the root DSE (DSA-Specific Entry),
427 which is named with the zero-length LDAPDN. These attributes are
428 retrievable if a client performs a base object search of the root
429 with filter "(objectClass=*)", however they are subject to access
430 control restrictions. The root DSE MUST NOT be included if the
431 client performs a subtree search starting from the root.
433 Servers may allow clients to modify these attributes.
435 The following attributes of the root DSE are defined in section 5 of
436 [5]. Additional attributes may be defined in other documents.
438 - namingContexts: naming contexts held in the server. Naming contexts
439 are defined in section 17 of X.501 [6].
441 - subschemaSubentry: subschema entries (or subentries) known by this
444 - altServer: alternative servers in case this one is later
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452 RFC 2251 LDAPv3 December 1997
455 - supportedExtension: list of supported extended operations.
457 - supportedControl: list of supported controls.
459 - supportedSASLMechanisms: list of supported SASL security features.
461 - supportedLDAPVersion: LDAP versions implemented by the server.
463 If the server does not master entries and does not know the locations
464 of schema information, the subschemaSubentry attribute is not present
465 in the root DSE. If the server masters directory entries under one
466 or more schema rules, there may be any number of values of the
467 subschemaSubentry attribute in the root DSE.
469 4. Elements of Protocol
471 The LDAP protocol is described using Abstract Syntax Notation 1
472 (ASN.1) [3], and is typically transferred using a subset of ASN.1
473 Basic Encoding Rules [11]. In order to support future extensions to
474 this protocol, clients and servers MUST ignore elements of SEQUENCE
475 encodings whose tags they do not recognize.
477 Note that unlike X.500, each change to the LDAP protocol other than
478 through the extension mechanisms will have a different version
479 number. A client will indicate the version it supports as part of
480 the bind request, described in section 4.2. If a client has not sent
481 a bind, the server MUST assume that version 3 is supported in the
482 client (since version 2 required that the client bind first).
484 Clients may determine the protocol version a server supports by
485 reading the supportedLDAPVersion attribute from the root DSE. Servers
486 which implement version 3 or later versions MUST provide this
487 attribute. Servers which only implement version 2 may not provide
492 This section describes the LDAPMessage envelope PDU (Protocol Data
493 Unit) format, as well as data type definitions which are used in the
496 4.1.1. Message Envelope
498 For the purposes of protocol exchanges, all protocol operations are
499 encapsulated in a common envelope, the LDAPMessage, which is defined
502 LDAPMessage ::= SEQUENCE {
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508 RFC 2251 LDAPv3 December 1997
513 bindRequest BindRequest,
514 bindResponse BindResponse,
515 unbindRequest UnbindRequest,
516 searchRequest SearchRequest,
517 searchResEntry SearchResultEntry,
518 searchResDone SearchResultDone,
519 searchResRef SearchResultReference,
520 modifyRequest ModifyRequest,
521 modifyResponse ModifyResponse,
522 addRequest AddRequest,
523 addResponse AddResponse,
524 delRequest DelRequest,
525 delResponse DelResponse,
526 modDNRequest ModifyDNRequest,
527 modDNResponse ModifyDNResponse,
528 compareRequest CompareRequest,
529 compareResponse CompareResponse,
530 abandonRequest AbandonRequest,
531 extendedReq ExtendedRequest,
532 extendedResp ExtendedResponse },
533 controls [0] Controls OPTIONAL }
535 MessageID ::= INTEGER (0 .. maxInt)
537 maxInt INTEGER ::= 2147483647 -- (2^^31 - 1) --
539 The function of the LDAPMessage is to provide an envelope containing
540 common fields required in all protocol exchanges. At this time the
541 only common fields are the message ID and the controls.
543 If the server receives a PDU from the client in which the LDAPMessage
544 SEQUENCE tag cannot be recognized, the messageID cannot be parsed,
545 the tag of the protocolOp is not recognized as a request, or the
546 encoding structures or lengths of data fields are found to be
547 incorrect, then the server MUST return the notice of disconnection
548 described in section 4.4.1, with resultCode protocolError, and
549 immediately close the connection. In other cases that the server
550 cannot parse the request received by the client, the server MUST
551 return an appropriate response to the request, with the resultCode
552 set to protocolError.
554 If the client receives a PDU from the server which cannot be parsed,
555 the client may discard the PDU, or may abruptly close the connection.
557 The ASN.1 type Controls is defined in section 4.1.12.
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564 RFC 2251 LDAPv3 December 1997
569 All LDAPMessage envelopes encapsulating responses contain the
570 messageID value of the corresponding request LDAPMessage.
572 The message ID of a request MUST have a value different from the
573 values of any other requests outstanding in the LDAP session of which
574 this message is a part.
576 A client MUST NOT send a second request with the same message ID as
577 an earlier request on the same connection if the client has not
578 received the final response from the earlier request. Otherwise the
579 behavior is undefined. Typical clients increment a counter for each
582 A client MUST NOT reuse the message id of an abandonRequest or of the
583 abandoned operation until it has received a response from the server
584 for another request invoked subsequent to the abandonRequest, as the
585 abandonRequest itself does not have a response.
589 The LDAPString is a notational convenience to indicate that, although
590 strings of LDAPString type encode as OCTET STRING types, the ISO
591 10646 [13] character set (a superset of Unicode) is used, encoded
592 following the UTF-8 algorithm [14]. Note that in the UTF-8 algorithm
593 characters which are the same as ASCII (0x0000 through 0x007F) are
594 represented as that same ASCII character in a single byte. The other
595 byte values are used to form a variable-length encoding of an
598 LDAPString ::= OCTET STRING
600 The LDAPOID is a notational convenience to indicate that the
601 permitted value of this string is a (UTF-8 encoded) dotted-decimal
602 representation of an OBJECT IDENTIFIER.
604 LDAPOID ::= OCTET STRING
608 1.3.6.1.4.1.1466.1.2.3
610 4.1.3. Distinguished Name and Relative Distinguished Name
612 An LDAPDN and a RelativeLDAPDN are respectively defined to be the
613 representation of a Distinguished Name and a Relative Distinguished
614 Name after encoding according to the specification in [4], such that
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620 RFC 2251 LDAPv3 December 1997
623 <distinguished-name> ::= <name>
625 <relative-distinguished-name> ::= <name-component>
627 where <name> and <name-component> are as defined in [4].
629 LDAPDN ::= LDAPString
631 RelativeLDAPDN ::= LDAPString
633 Only Attribute Types can be present in a relative distinguished name
634 component; the options of Attribute Descriptions (next section) MUST
635 NOT be used in specifying distinguished names.
637 4.1.4. Attribute Type
639 An AttributeType takes on as its value the textual string associated
640 with that AttributeType in its specification.
642 AttributeType ::= LDAPString
644 Each attribute type has a unique OBJECT IDENTIFIER which has been
645 assigned to it. This identifier may be written as decimal digits
646 with components separated by periods, e.g. "2.5.4.10".
648 A specification may also assign one or more textual names for an
649 attribute type. These names MUST begin with a letter, and only
650 contain ASCII letters, digit characters and hyphens. They are case
651 insensitive. (These ASCII characters are identical to ISO 10646
652 characters whose UTF-8 encoding is a single byte between 0x00 and
655 If the server has a textual name for an attribute type, it MUST use a
656 textual name for attributes returned in search results. The dotted-
657 decimal OBJECT IDENTIFIER is only used if there is no textual name
658 for an attribute type.
660 Attribute type textual names are non-unique, as two different
661 specifications (neither in standards track RFCs) may choose the same
664 A server which masters or shadows entries SHOULD list all the
665 attribute types it supports in the subschema entries, using the
666 attributeTypes attribute. Servers which support an open-ended set of
667 attributes SHOULD include at least the attributeTypes value for the
668 'objectClass' attribute. Clients MAY retrieve the attributeTypes
669 value from subschema entries in order to obtain the OBJECT IDENTIFIER
670 and other information associated with attribute types.
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679 Some attribute type names which are used in this version of LDAP are
680 described in [5]. Servers may implement additional attribute types.
682 4.1.5. Attribute Description
684 An AttributeDescription is a superset of the definition of the
685 AttributeType. It has the same ASN.1 definition, but allows
686 additional options to be specified. They are also case insensitive.
688 AttributeDescription ::= LDAPString
690 A value of AttributeDescription is based on the following BNF:
692 <AttributeDescription> ::= <AttributeType> [ ";" <options> ]
694 <options> ::= <option> | <option> ";" <options>
696 <option> ::= <opt-char> <opt-char>*
698 <opt-char> ::= ASCII-equivalent letters, numbers and hyphen
700 Examples of valid AttributeDescription:
703 userCertificate;binary
705 One option, "binary", is defined in this document. Additional
706 options may be defined in IETF standards-track and experimental RFCs.
707 Options beginning with "x-" are reserved for private experiments.
708 Any option could be associated with any AttributeType, although not
709 all combinations may be supported by a server.
711 An AttributeDescription with one or more options is treated as a
712 subtype of the attribute type without any options. Options present
713 in an AttributeDescription are never mutually exclusive.
714 Implementations MUST generate the <options> list sorted in ascending
715 order, and servers MUST treat any two AttributeDescription with the
716 same AttributeType and options as equivalent. A server will treat an
717 AttributeDescription with any options it does not implement as an
718 unrecognized attribute type.
720 The data type "AttributeDescriptionList" describes a list of 0 or
721 more attribute types. (A list of zero elements has special
722 significance in the Search request.)
724 AttributeDescriptionList ::= SEQUENCE OF
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732 RFC 2251 LDAPv3 December 1997
735 4.1.5.1. Binary Option
737 If the "binary" option is present in an AttributeDescription, it
738 overrides any string-based encoding representation defined for that
739 attribute in [5]. Instead the attribute is to be transferred as a
740 binary value encoded using the Basic Encoding Rules [11]. The syntax
741 of the binary value is an ASN.1 data type definition which is
742 referenced by the "SYNTAX" part of the attribute type definition.
744 The presence or absence of the "binary" option only affects the
745 transfer of attribute values in protocol; servers store any
746 particular attribute in a single format. If a client requests that a
747 server return an attribute in the binary format, but the server
748 cannot generate that format, the server MUST treat this attribute
749 type as an unrecognized attribute type. Similarly, clients MUST NOT
750 expect servers to return an attribute in binary format if the client
751 requested that attribute by name without the binary option.
753 This option is intended to be used with attributes whose syntax is a
754 complex ASN.1 data type, and the structure of values of that type is
755 needed by clients. Examples of this kind of syntax are "Certificate"
756 and "CertificateList".
758 4.1.6. Attribute Value
760 A field of type AttributeValue takes on as its value either a string
761 encoding of a AttributeValue data type, or an OCTET STRING containing
762 an encoded binary value, depending on whether the "binary" option is
763 present in the companion AttributeDescription to this AttributeValue.
765 The definition of string encodings for different syntaxes and types
766 may be found in other documents, and in particular [5].
768 AttributeValue ::= OCTET STRING
770 Note that there is no defined limit on the size of this encoding;
771 thus protocol values may include multi-megabyte attributes (e.g.
774 Attributes may be defined which have arbitrary and non-printable
775 syntax. Implementations MUST NEITHER simply display nor attempt to
776 decode as ASN.1 a value if its syntax is not known. The
777 implementation may attempt to discover the subschema of the source
778 entry, and retrieve the values of attributeTypes from it.
780 Clients MUST NOT send attribute values in a request which are not
781 valid according to the syntax defined for the attributes.
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788 RFC 2251 LDAPv3 December 1997
791 4.1.7. Attribute Value Assertion
793 The AttributeValueAssertion type definition is similar to the one in
794 the X.500 directory standards. It contains an attribute description
795 and a matching rule assertion value suitable for that type.
797 AttributeValueAssertion ::= SEQUENCE {
798 attributeDesc AttributeDescription,
799 assertionValue AssertionValue }
801 AssertionValue ::= OCTET STRING
803 If the "binary" option is present in attributeDesc, this signals to
804 the server that the assertionValue is a binary encoding of the
807 For all the string-valued user attributes described in [5], the
808 assertion value syntax is the same as the value syntax. Clients may
809 use attribute values as assertion values in compare requests and
812 Note however that the assertion syntax may be different from the
813 value syntax for other attributes or for non-equality matching rules.
814 These may have an assertion syntax which contains only part of the
815 value. See section 20.2.1.8 of X.501 [6] for examples.
819 An attribute consists of a type and one or more values of that type.
820 (Though attributes MUST have at least one value when stored, due to
821 access control restrictions the set may be empty when transferred in
822 protocol. This is described in section 4.5.2, concerning the
823 PartialAttributeList type.)
825 Attribute ::= SEQUENCE {
826 type AttributeDescription,
827 vals SET OF AttributeValue }
829 Each attribute value is distinct in the set (no duplicates). The
830 order of attribute values within the vals set is undefined and
831 implementation-dependent, and MUST NOT be relied upon.
833 4.1.9. Matching Rule Identifier
835 A matching rule is a means of expressing how a server should compare
836 an AssertionValue received in a search filter with an abstract data
837 value. The matching rule defines the syntax of the assertion value
838 and the process to be performed in the server.
842 Wahl, et. al. Standards Track [Page 15]
844 RFC 2251 LDAPv3 December 1997
847 An X.501(1993) Matching Rule is identified in the LDAP protocol by
848 the printable representation of its OBJECT IDENTIFIER, either as one
849 of the strings given in [5], or as decimal digits with components
850 separated by periods, e.g. "caseIgnoreIA5Match" or
851 "1.3.6.1.4.1.453.33.33".
853 MatchingRuleId ::= LDAPString
855 Servers which support matching rules for use in the extensibleMatch
856 search filter MUST list the matching rules they implement in
857 subschema entries, using the matchingRules attributes. The server
858 SHOULD also list there, using the matchingRuleUse attribute, the
859 attribute types with which each matching rule can be used. More
860 information is given in section 4.4 of [5].
862 4.1.10. Result Message
864 The LDAPResult is the construct used in this protocol to return
865 success or failure indications from servers to clients. In response
866 to various requests servers will return responses containing fields
867 of type LDAPResult to indicate the final status of a protocol
870 LDAPResult ::= SEQUENCE {
871 resultCode ENUMERATED {
875 timeLimitExceeded (3),
876 sizeLimitExceeded (4),
880 authMethodNotSupported (7),
881 strongAuthRequired (8),
883 referral (10), -- new
884 adminLimitExceeded (11), -- new
885 unavailableCriticalExtension (12), -- new
886 confidentialityRequired (13), -- new
887 saslBindInProgress (14), -- new
888 noSuchAttribute (16),
889 undefinedAttributeType (17),
890 inappropriateMatching (18),
891 constraintViolation (19),
892 attributeOrValueExists (20),
893 invalidAttributeSyntax (21),
898 Wahl, et. al. Standards Track [Page 16]
900 RFC 2251 LDAPv3 December 1997
905 invalidDNSyntax (34),
906 -- 35 reserved for undefined isLeaf --
907 aliasDereferencingProblem (36),
909 inappropriateAuthentication (48),
910 invalidCredentials (49),
911 insufficientAccessRights (50),
914 unwillingToPerform (53),
917 namingViolation (64),
918 objectClassViolation (65),
919 notAllowedOnNonLeaf (66),
920 notAllowedOnRDN (67),
921 entryAlreadyExists (68),
922 objectClassModsProhibited (69),
923 -- 70 reserved for CLDAP --
924 affectsMultipleDSAs (71), -- new
927 -- 81-90 reserved for APIs --
929 errorMessage LDAPString,
930 referral [3] Referral OPTIONAL }
932 All the result codes with the exception of success, compareFalse and
933 compareTrue are to be treated as meaning the operation could not be
934 completed in its entirety.
936 Most of the result codes are based on problem indications from X.511
937 error data types. Result codes from 16 to 21 indicate an
938 AttributeProblem, codes 32, 33, 34 and 36 indicate a NameProblem,
939 codes 48, 49 and 50 indicate a SecurityProblem, codes 51 to 54
940 indicate a ServiceProblem, and codes 64 to 69 and 71 indicates an
943 If a client receives a result code which is not listed above, it is
944 to be treated as an unknown error condition.
946 The errorMessage field of this construct may, at the server's option,
947 be used to return a string containing a textual, human-readable
948 (terminal control and page formatting characters should be avoided)
949 error diagnostic. As this error diagnostic is not standardized,
954 Wahl, et. al. Standards Track [Page 17]
956 RFC 2251 LDAPv3 December 1997
959 implementations MUST NOT rely on the values returned. If the server
960 chooses not to return a textual diagnostic, the errorMessage field of
961 the LDAPResult type MUST contain a zero length string.
963 For result codes of noSuchObject, aliasProblem, invalidDNSyntax and
964 aliasDereferencingProblem, the matchedDN field is set to the name of
965 the lowest entry (object or alias) in the directory that was matched.
966 If no aliases were dereferenced while attempting to locate the entry,
967 this will be a truncated form of the name provided, or if aliases
968 were dereferenced, of the resulting name, as defined in section 12.5
969 of X.511 [8]. The matchedDN field is to be set to a zero length
970 string with all other result codes.
974 The referral error indicates that the contacted server does not hold
975 the target entry of the request. The referral field is present in an
976 LDAPResult if the LDAPResult.resultCode field value is referral, and
977 absent with all other result codes. It contains a reference to
978 another server (or set of servers) which may be accessed via LDAP or
979 other protocols. Referrals can be returned in response to any
980 operation request (except unbind and abandon which do not have
981 responses). At least one URL MUST be present in the Referral.
983 The referral is not returned for a singleLevel or wholeSubtree search
984 in which the search scope spans multiple naming contexts, and several
985 different servers would need to be contacted to complete the
986 operation. Instead, continuation references, described in section
989 Referral ::= SEQUENCE OF LDAPURL -- one or more
991 LDAPURL ::= LDAPString -- limited to characters permitted in URLs
993 If the client wishes to progress the operation, it MUST follow the
994 referral by contacting any one of servers. All the URLs MUST be
995 equally capable of being used to progress the operation. (The
996 mechanisms for how this is achieved by multiple servers are outside
997 the scope of this document.)
999 URLs for servers implementing the LDAP protocol are written according
1000 to [9]. If an alias was dereferenced, the <dn> part of the URL MUST
1001 be present, with the new target object name. If the <dn> part is
1002 present, the client MUST use this name in its next request to
1003 progress the operation, and if it is not present the client will use
1004 the same name as in the original request. Some servers (e.g.
1005 participating in distributed indexing) may provide a different filter
1006 in a referral for a search operation. If the filter part of the URL
1010 Wahl, et. al. Standards Track [Page 18]
1012 RFC 2251 LDAPv3 December 1997
1015 is present in an LDAPURL, the client MUST use this filter in its next
1016 request to progress this search, and if it is not present the client
1017 MUST use the same filter as it used for that search. Other aspects
1018 of the new request may be the same or different as the request which
1019 generated the referral.
1021 Note that UTF-8 characters appearing in a DN or search filter may not
1022 be legal for URLs (e.g. spaces) and MUST be escaped using the %
1023 method in RFC 1738 [7].
1025 Other kinds of URLs may be returned, so long as the operation could
1026 be performed using that protocol.
1030 A control is a way to specify extension information. Controls which
1031 are sent as part of a request apply only to that request and are not
1034 Controls ::= SEQUENCE OF Control
1036 Control ::= SEQUENCE {
1037 controlType LDAPOID,
1038 criticality BOOLEAN DEFAULT FALSE,
1039 controlValue OCTET STRING OPTIONAL }
1041 The controlType field MUST be a UTF-8 encoded dotted-decimal
1042 representation of an OBJECT IDENTIFIER which uniquely identifies the
1043 control. This prevents conflicts between control names.
1045 The criticality field is either TRUE or FALSE.
1047 If the server recognizes the control type and it is appropriate for
1048 the operation, the server will make use of the control when
1049 performing the operation.
1051 If the server does not recognize the control type and the criticality
1052 field is TRUE, the server MUST NOT perform the operation, and MUST
1053 instead return the resultCode unsupportedCriticalExtension.
1055 If the control is not appropriate for the operation and criticality
1056 field is TRUE, the server MUST NOT perform the operation, and MUST
1057 instead return the resultCode unsupportedCriticalExtension.
1059 If the control is unrecognized or inappropriate but the criticality
1060 field is FALSE, the server MUST ignore the control.
1066 Wahl, et. al. Standards Track [Page 19]
1068 RFC 2251 LDAPv3 December 1997
1071 The controlValue contains any information associated with the
1072 control, and its format is defined for the control. The server MUST
1073 be prepared to handle arbitrary contents of the controlValue octet
1074 string, including zero bytes. It is absent only if there is no value
1075 information which is associated with a control of its type.
1077 This document does not define any controls. Controls may be defined
1078 in other documents. The definition of a control consists of:
1080 - the OBJECT IDENTIFIER assigned to the control,
1082 - whether the control is always noncritical, always critical, or
1083 critical at the client's option,
1085 - the format of the controlValue contents of the control.
1087 Servers list the controls which they recognize in the
1088 supportedControl attribute in the root DSE.
1092 The function of the Bind Operation is to allow authentication
1093 information to be exchanged between the client and server.
1095 The Bind Request is defined as follows:
1097 BindRequest ::= [APPLICATION 0] SEQUENCE {
1098 version INTEGER (1 .. 127),
1100 authentication AuthenticationChoice }
1102 AuthenticationChoice ::= CHOICE {
1103 simple [0] OCTET STRING,
1105 sasl [3] SaslCredentials }
1107 SaslCredentials ::= SEQUENCE {
1108 mechanism LDAPString,
1109 credentials OCTET STRING OPTIONAL }
1111 Parameters of the Bind Request are:
1113 - version: A version number indicating the version of the protocol to
1114 be used in this protocol session. This document describes version
1115 3 of the LDAP protocol. Note that there is no version negotiation,
1116 and the client just sets this parameter to the version it desires.
1117 If the client requests protocol version 2, a server that supports
1118 the version 2 protocol as described in [2] will not return any v3-
1122 Wahl, et. al. Standards Track [Page 20]
1124 RFC 2251 LDAPv3 December 1997
1127 specific protocol fields. (Note that not all LDAP servers will
1128 support protocol version 2, since they may be unable to generate
1129 the attribute syntaxes associated with version 2.)
1131 - name: The name of the directory object that the client wishes to
1132 bind as. This field may take on a null value (a zero length
1133 string) for the purposes of anonymous binds, when authentication
1134 has been performed at a lower layer, or when using SASL credentials
1135 with a mechanism that includes the LDAPDN in the credentials.
1137 - authentication: information used to authenticate the name, if any,
1138 provided in the Bind Request.
1140 Upon receipt of a Bind Request, a protocol server will authenticate
1141 the requesting client, if necessary. The server will then return a
1142 Bind Response to the client indicating the status of the
1145 Authorization is the use of this authentication information when
1146 performing operations. Authorization MAY be affected by factors
1147 outside of the LDAP Bind request, such as lower layer security
1150 4.2.1. Sequencing of the Bind Request
1152 For some SASL authentication mechanisms, it may be necessary for the
1153 client to invoke the BindRequest multiple times. If at any stage the
1154 client wishes to abort the bind process it MAY unbind and then drop
1155 the underlying connection. Clients MUST NOT invoke operations
1156 between two Bind requests made as part of a multi-stage bind.
1158 A client may abort a SASL bind negotiation by sending a BindRequest
1159 with a different value in the mechanism field of SaslCredentials, or
1160 an AuthenticationChoice other than sasl.
1162 If the client sends a BindRequest with the sasl mechanism field as an
1163 empty string, the server MUST return a BindResponse with
1164 authMethodNotSupported as the resultCode. This will allow clients to
1165 abort a negotiation if it wishes to try again with the same SASL
1168 Unlike LDAP v2, the client need not send a Bind Request in the first
1169 PDU of the connection. The client may request any operations and the
1170 server MUST treat these as unauthenticated. If the server requires
1171 that the client bind before browsing or modifying the directory, the
1172 server MAY reject a request other than binding, unbinding or an
1173 extended request with the "operationsError" result.
1178 Wahl, et. al. Standards Track [Page 21]
1180 RFC 2251 LDAPv3 December 1997
1183 If the client did not bind before sending a request and receives an
1184 operationsError, it may then send a Bind Request. If this also fails
1185 or the client chooses not to bind on the existing connection, it will
1186 close the connection, reopen it and begin again by first sending a
1187 PDU with a Bind Request. This will aid in interoperating with
1188 servers implementing other versions of LDAP.
1190 Clients MAY send multiple bind requests on a connection to change
1191 their credentials. A subsequent bind process has the effect of
1192 abandoning all operations outstanding on the connection. (This
1193 simplifies server implementation.) Authentication from earlier binds
1194 are subsequently ignored, and so if the bind fails, the connection
1195 will be treated as anonymous. If a SASL transfer encryption or
1196 integrity mechanism has been negotiated, and that mechanism does not
1197 support the changing of credentials from one identity to another,
1198 then the client MUST instead establish a new connection.
1200 4.2.2. Authentication and Other Security Services
1202 The simple authentication option provides minimal authentication
1203 facilities, with the contents of the authentication field consisting
1204 only of a cleartext password. Note that the use of cleartext
1205 passwords is not recommended over open networks when there is no
1206 authentication or encryption being performed by a lower layer; see
1207 the "Security Considerations" section.
1209 If no authentication is to be performed, then the simple
1210 authentication option MUST be chosen, and the password be of zero
1211 length. (This is often done by LDAPv2 clients.) Typically the DN is
1212 also of zero length.
1214 The sasl choice allows for any mechanism defined for use with SASL
1215 [12]. The mechanism field contains the name of the mechanism. The
1216 credentials field contains the arbitrary data used for
1217 authentication, inside an OCTET STRING wrapper. Note that unlike
1218 some Internet application protocols where SASL is used, LDAP is not
1219 text-based, thus no base64 transformations are performed on the
1222 If any SASL-based integrity or confidentiality services are enabled,
1223 they take effect following the transmission by the server and
1224 reception by the client of the final BindResponse with resultCode
1227 The client can request that the server use authentication information
1228 from a lower layer protocol by using the SASL EXTERNAL mechanism.
1234 Wahl, et. al. Standards Track [Page 22]
1236 RFC 2251 LDAPv3 December 1997
1239 4.2.3. Bind Response
1241 The Bind Response is defined as follows.
1243 BindResponse ::= [APPLICATION 1] SEQUENCE {
1244 COMPONENTS OF LDAPResult,
1245 serverSaslCreds [7] OCTET STRING OPTIONAL }
1247 BindResponse consists simply of an indication from the server of he
1248 status of the client's request for authentication.
1250 f the bind was successful, the resultCode will be success, therwise
1253 - operationsError: server encountered an internal error,
1255 - protocolError: unrecognized version number or incorrect PDU
1258 - authMethodNotSupported: unrecognized SASL mechanism name,
1260 - strongAuthRequired: the server requires authentication be
1261 performed with a SASL mechanism,
1263 - referral: this server cannot accept this bind and the client
1266 - saslBindInProgress: the server requires the client to send a
1267 new bind request, with the same sasl mechanism, to continue the
1268 authentication process,
1270 - inappropriateAuthentication: the server requires the client
1271 which had attempted to bind anonymously or without supplying
1272 credentials to provide some form of credentials,
1274 - invalidCredentials: the wrong password was supplied or the SASL
1275 credentials could not be processed,
1277 - unavailable: the server is shutting down.
1279 If the server does not support the client's requested protocol
1280 version, it MUST set the resultCode to protocolError.
1282 If the client receives a BindResponse response where the resultCode
1283 was protocolError, it MUST close the connection as the server will be
1284 unwilling to accept further operations. (This is for compatibility
1285 with earlier versions of LDAP, in which the bind was always the first
1286 operation, and there was no negotiation.)
1290 Wahl, et. al. Standards Track [Page 23]
1292 RFC 2251 LDAPv3 December 1997
1295 The serverSaslCreds are used as part of a SASL-defined bind mechanism
1296 to allow the client to authenticate the server to which it is
1297 communicating, or to perform "challenge-response" authentication. If
1298 the client bound with the password choice, or the SASL mechanism does
1299 not require the server to return information to the client, then this
1300 field is not to be included in the result.
1302 4.3. Unbind Operation
1304 The function of the Unbind Operation is to terminate a protocol
1305 session. The Unbind Operation is defined as follows:
1307 UnbindRequest ::= [APPLICATION 2] NULL
1309 The Unbind Operation has no response defined. Upon transmission of an
1310 UnbindRequest, a protocol client may assume that the protocol session
1311 is terminated. Upon receipt of an UnbindRequest, a protocol server
1312 may assume that the requesting client has terminated the session and
1313 that all outstanding requests may be discarded, and may close the
1316 4.4. Unsolicited Notification
1318 An unsolicited notification is an LDAPMessage sent from the server to
1319 the client which is not in response to any LDAPMessage received by
1320 the server. It is used to signal an extraordinary condition in the
1321 server or in the connection between the client and the server. The
1322 notification is of an advisory nature, and the server will not expect
1323 any response to be returned from the client.
1325 The unsolicited notification is structured as an LDAPMessage in which
1326 the messageID is 0 and protocolOp is of the extendedResp form. The
1327 responseName field of the ExtendedResponse is present. The LDAPOID
1328 value MUST be unique for this notification, and not be used in any
1331 One unsolicited notification is defined in this document.
1333 4.4.1. Notice of Disconnection
1335 This notification may be used by the server to advise the client that
1336 the server is about to close the connection due to an error
1337 condition. Note that this notification is NOT a response to an
1338 unbind requested by the client: the server MUST follow the procedures
1339 of section 4.3. This notification is intended to assist clients in
1340 distinguishing between an error condition and a transient network
1346 Wahl, et. al. Standards Track [Page 24]
1348 RFC 2251 LDAPv3 December 1997
1351 failure. As with a connection close due to network failure, the
1352 client MUST NOT assume that any outstanding requests which modified
1353 the directory have succeeded or failed.
1355 The responseName is 1.3.6.1.4.1.1466.20036, the response field is
1356 absent, and the resultCode is used to indicate the reason for the
1359 The following resultCode values are to be used in this notification:
1361 - protocolError: The server has received data from the client in
1363 the LDAPMessage structure could not be parsed.
1365 - strongAuthRequired: The server has detected that an established
1366 underlying security association protecting communication between
1367 the client and server has unexpectedly failed or been compromised.
1369 - unavailable: This server will stop accepting new connections and
1370 operations on all existing connections, and be unavailable for an
1371 extended period of time. The client may make use of an alternative
1374 After sending this notice, the server MUST close the connection.
1375 After receiving this notice, the client MUST NOT transmit any further
1376 on the connection, and may abruptly close the connection.
1378 4.5. Search Operation
1380 The Search Operation allows a client to request that a search be
1381 performed on its behalf by a server. This can be used to read
1382 attributes from a single entry, from entries immediately below a
1383 particular entry, or a whole subtree of entries.
1385 4.5.1. Search Request
1387 The Search Request is defined as follows:
1389 SearchRequest ::= [APPLICATION 3] SEQUENCE {
1395 derefAliases ENUMERATED {
1396 neverDerefAliases (0),
1397 derefInSearching (1),
1398 derefFindingBaseObj (2),
1402 Wahl, et. al. Standards Track [Page 25]
1404 RFC 2251 LDAPv3 December 1997
1408 sizeLimit INTEGER (0 .. maxInt),
1409 timeLimit INTEGER (0 .. maxInt),
1412 attributes AttributeDescriptionList }
1415 and [0] SET OF Filter,
1416 or [1] SET OF Filter,
1418 equalityMatch [3] AttributeValueAssertion,
1419 substrings [4] SubstringFilter,
1420 greaterOrEqual [5] AttributeValueAssertion,
1421 lessOrEqual [6] AttributeValueAssertion,
1422 present [7] AttributeDescription,
1423 approxMatch [8] AttributeValueAssertion,
1424 extensibleMatch [9] MatchingRuleAssertion }
1426 SubstringFilter ::= SEQUENCE {
1427 type AttributeDescription,
1428 -- at least one must be present
1429 substrings SEQUENCE OF CHOICE {
1430 initial [0] LDAPString,
1432 final [2] LDAPString } }
1434 MatchingRuleAssertion ::= SEQUENCE {
1435 matchingRule [1] MatchingRuleId OPTIONAL,
1436 type [2] AttributeDescription OPTIONAL,
1437 matchValue [3] AssertionValue,
1438 dnAttributes [4] BOOLEAN DEFAULT FALSE }
1440 Parameters of the Search Request are:
1442 - baseObject: An LDAPDN that is the base object entry relative to
1443 which the search is to be performed.
1445 - scope: An indicator of the scope of the search to be performed. The
1446 semantics of the possible values of this field are identical to the
1447 semantics of the scope field in the X.511 Search Operation.
1449 - derefAliases: An indicator as to how alias objects (as defined in
1450 X.501) are to be handled in searching. The semantics of the
1451 possible values of this field are:
1453 neverDerefAliases: do not dereference aliases in searching
1454 or in locating the base object of the search;
1458 Wahl, et. al. Standards Track [Page 26]
1460 RFC 2251 LDAPv3 December 1997
1463 derefInSearching: dereference aliases in subordinates of
1464 the base object in searching, but not in locating the
1465 base object of the search;
1467 derefFindingBaseObj: dereference aliases in locating
1468 the base object of the search, but not when searching
1469 subordinates of the base object;
1471 derefAlways: dereference aliases both in searching and in
1472 locating the base object of the search.
1474 - sizelimit: A sizelimit that restricts the maximum number of entries
1475 to be returned as a result of the search. A value of 0 in this
1476 field indicates that no client-requested sizelimit restrictions are
1477 in effect for the search. Servers may enforce a maximum number of
1480 - timelimit: A timelimit that restricts the maximum time (in seconds)
1481 allowed for a search. A value of 0 in this field indicates that no
1482 client-requested timelimit restrictions are in effect for the
1485 - typesOnly: An indicator as to whether search results will contain
1486 both attribute types and values, or just attribute types. Setting
1487 this field to TRUE causes only attribute types (no values) to be
1488 returned. Setting this field to FALSE causes both attribute types
1489 and values to be returned.
1491 - filter: A filter that defines the conditions that must be fulfilled
1492 in order for the search to match a given entry.
1494 The 'and', 'or' and 'not' choices can be used to form combinations of
1495 filters. At least one filter element MUST be present in an 'and' or
1496 'or' choice. The others match against individual attribute values of
1497 entries in the scope of the search. (Implementor's note: the 'not'
1498 filter is an example of a tagged choice in an implicitly-tagged
1499 module. In BER this is treated as if the tag was explicit.)
1501 A server MUST evaluate filters according to the three-valued logic
1502 of X.511(93) section 7.8.1. In summary, a filter is evaluated to
1503 either "TRUE", "FALSE" or "Undefined". If the filter evaluates
1504 to TRUE for a particular entry, then the attributes of that entry
1505 are returned as part of the search result (subject to any applicable
1506 access control restrictions). If the filter evaluates to FALSE or
1507 Undefined, then the entry is ignored for the search.
1514 Wahl, et. al. Standards Track [Page 27]
1516 RFC 2251 LDAPv3 December 1997
1519 A filter of the "and" choice is TRUE if all the filters in the SET
1520 OF evaluate to TRUE, FALSE if at least one filter is FALSE, and
1521 otherwise Undefined. A filter of the "or" choice is FALSE if all
1522 of the filters in the SET OF evaluate to FALSE, TRUE if at least
1523 one filter is TRUE, and Undefined otherwise. A filter of the "not"
1524 choice is TRUE if the filter being negated is FALSE, FALSE if it is
1525 TRUE, and Undefined if it is Undefined.
1527 The present match evaluates to TRUE where there is an attribute or
1528 subtype of the specified attribute description present in an entry,
1529 and FALSE otherwise (including a presence test with an unrecognized
1530 attribute description.)
1532 The extensibleMatch is new in this version of LDAP. If the
1533 matchingRule field is absent, the type field MUST be present, and
1534 the equality match is performed for that type. If the type field is
1535 absent and matchingRule is present, the matchValue is compared
1536 against all attributes in an entry which support that matchingRule,
1537 and the matchingRule determines the syntax for the assertion value
1538 (the filter item evaluates to TRUE if it matches with at least
1539 one attribute in the entry, FALSE if it does not match any attribute
1540 in the entry, and Undefined if the matchingRule is not recognized
1541 or the assertionValue cannot be parsed.) If the type field is
1542 present and matchingRule is present, the matchingRule MUST be one
1543 permitted for use with that type, otherwise the filter item is
1544 undefined. If the dnAttributes field is set to TRUE, the match is
1545 applied against all the attributes in an entry's distinguished name
1546 as well, and also evaluates to TRUE if there is at least one
1547 attribute in the distinguished name for which the filter item
1548 evaluates to TRUE. (Editors note: The dnAttributes field is present
1549 so that there does not need to be multiple versions of generic
1550 matching rules such as for word matching, one to apply to entries
1551 and another to apply to entries and dn attributes as well).
1553 A filter item evaluates to Undefined when the server would not
1554 be able to determine whether the assertion value matches an
1555 entry. If an attribute description in an equalityMatch, substrings,
1556 greaterOrEqual, lessOrEqual, approxMatch or extensibleMatch
1557 filter is not recognized by the server, a matching rule id in the
1558 extensibleMatch is not recognized by the server, the assertion
1559 value cannot be parsed, or the type of filtering requested is not
1560 implemented, then the filter is Undefined. Thus for example if a
1561 server did not recognize the attribute type shoeSize, a filter of
1562 (shoeSize=*) would evaluate to FALSE, and the filters (shoeSize=12),
1563 (shoeSize>=12) and (shoeSize<=12) would evaluate to Undefined.
1570 Wahl, et. al. Standards Track [Page 28]
1572 RFC 2251 LDAPv3 December 1997
1575 Servers MUST NOT return errors if attribute descriptions or matching
1576 rule ids are not recognized, or assertion values cannot be parsed.
1577 More details of filter processing are given in section 7.8 of X.511
1580 - attributes: A list of the attributes to be returned from each entry
1581 which matches the search filter. There are two special values which
1582 may be used: an empty list with no attributes, and the attribute
1583 description string "*". Both of these signify that all user
1584 attributes are to be returned. (The "*" allows the client to
1585 request all user attributes in addition to specific operational
1588 Attributes MUST be named at most once in the list, and are returned
1589 at most once in an entry. If there are attribute descriptions in
1590 the list which are not recognized, they are ignored by the server.
1592 If the client does not want any attributes returned, it can specify
1593 a list containing only the attribute with OID "1.1". This OID was
1594 chosen arbitrarily and does not correspond to any attribute in use.
1596 Client implementors should note that even if all user attributes are
1597 requested, some attributes of the entry may not be included in
1598 search results due to access control or other restrictions.
1599 Furthermore, servers will not return operational attributes, such
1600 as objectClasses or attributeTypes, unless they are listed by name,
1601 since there may be extremely large number of values for certain
1602 operational attributes. (A list of operational attributes for use
1603 in LDAP is given in [5].)
1605 Note that an X.500 "list"-like operation can be emulated by the client
1606 requesting a one-level LDAP search operation with a filter checking
1607 for the existence of the objectClass attribute, and that an X.500
1608 "read"-like operation can be emulated by a base object LDAP search
1609 operation with the same filter. A server which provides a gateway to
1610 X.500 is not required to use the Read or List operations, although it
1611 may choose to do so, and if it does must provide the same semantics
1612 as the X.500 search operation.
1614 4.5.2. Search Result
1616 The results of the search attempted by the server upon receipt of a
1617 Search Request are returned in Search Responses, which are LDAP
1618 messages containing either SearchResultEntry, SearchResultReference,
1619 ExtendedResponse or SearchResultDone data types.
1621 SearchResultEntry ::= [APPLICATION 4] SEQUENCE {
1626 Wahl, et. al. Standards Track [Page 29]
1628 RFC 2251 LDAPv3 December 1997
1631 attributes PartialAttributeList }
1633 PartialAttributeList ::= SEQUENCE OF SEQUENCE {
1634 type AttributeDescription,
1635 vals SET OF AttributeValue }
1636 -- implementors should note that the PartialAttributeList may
1637 -- have zero elements (if none of the attributes of that entry
1638 -- were requested, or could be returned), and that the vals set
1639 -- may also have zero elements (if types only was requested, or
1640 -- all values were excluded from the result.)
1642 SearchResultReference ::= [APPLICATION 19] SEQUENCE OF LDAPURL
1643 -- at least one LDAPURL element must be present
1645 SearchResultDone ::= [APPLICATION 5] LDAPResult
1647 Upon receipt of a Search Request, a server will perform the necessary
1650 If the LDAP session is operating over a connection-oriented transport
1651 such as TCP, the server will return to the client a sequence of
1652 responses in separate LDAP messages. There may be zero or more
1653 responses containing SearchResultEntry, one for each entry found
1654 during the search. There may also be zero or more responses
1655 containing SearchResultReference, one for each area not explored by
1656 this server during the search. The SearchResultEntry and
1657 SearchResultReference PDUs may come in any order. Following all the
1658 SearchResultReference responses and all SearchResultEntry responses
1659 to be returned by the server, the server will return a response
1660 containing the SearchResultDone, which contains an indication of
1661 success, or detailing any errors that have occurred.
1663 Each entry returned in a SearchResultEntry will contain all
1664 attributes, complete with associated values if necessary, as
1665 specified in the attributes field of the Search Request. Return of
1666 attributes is subject to access control and other administrative
1667 policy. Some attributes may be returned in binary format (indicated
1668 by the AttributeDescription in the response having the binary option
1671 Some attributes may be constructed by the server and appear in a
1672 SearchResultEntry attribute list, although they are not stored
1673 attributes of an entry. Clients MUST NOT assume that all attributes
1674 can be modified, even if permitted by access control.
1676 LDAPMessage responses of the ExtendedResponse form are reserved for
1677 returning information associated with a control requested by the
1678 client. These may be defined in future versions of this document.
1682 Wahl, et. al. Standards Track [Page 30]
1684 RFC 2251 LDAPv3 December 1997
1687 4.5.3. Continuation References in the Search Result
1689 If the server was able to locate the entry referred to by the
1690 baseObject but was unable to search all the entries in the scope at
1691 and under the baseObject, the server may return one or more
1692 SearchResultReference, each containing a reference to another set of
1693 servers for continuing the operation. A server MUST NOT return any
1694 SearchResultReference if it has not located the baseObject and
1695 thus has not searched any entries; in this case it would return a
1696 SearchResultDone containing a referral resultCode.
1698 In the absence of indexing information provided to a server from
1699 servers holding subordinate naming contexts, SearchResultReference
1700 responses are not affected by search filters and are always returned
1703 The SearchResultReference is of the same data type as the Referral.
1704 URLs for servers implementing the LDAP protocol are written according
1705 to [9]. The <dn> part MUST be present in the URL, with the new target
1706 object name. The client MUST use this name in its next request.
1707 Some servers (e.g. part of a distributed index exchange system) may
1708 provide a different filter in the URLs of the SearchResultReference.
1709 If the filter part of the URL is present in an LDAP URL, the client
1710 MUST use the new filter in its next request to progress the search,
1711 and if the filter part is absent the client will use again the same
1712 filter. Other aspects of the new search request may be the same or
1713 different as the search which generated the continuation references.
1715 Other kinds of URLs may be returned so long as the operation could be
1716 performed using that protocol.
1718 The name of an unexplored subtree in a SearchResultReference need not
1719 be subordinate to the base object.
1721 In order to complete the search, the client MUST issue a new search
1722 operation for each SearchResultReference that is returned. Note that
1723 the abandon operation described in section 4.11 applies only to a
1724 particular operation sent on a connection between a client and server,
1725 and if the client has multiple outstanding search operations to
1726 different servers, it MUST abandon each operation individually.
1730 For example, suppose the contacted server (hosta) holds the entry
1731 "O=MNN,C=WW" and the entry "CN=Manager,O=MNN,C=WW". It knows that
1732 either LDAP-capable servers (hostb) or (hostc) hold
1733 "OU=People,O=MNN,C=WW" (one is the master and the other server a
1738 Wahl, et. al. Standards Track [Page 31]
1740 RFC 2251 LDAPv3 December 1997
1743 shadow), and that LDAP-capable server (hostd) holds the subtree
1744 "OU=Roles,O=MNN,C=WW". If a subtree search of "O=MNN,C=WW" is
1745 requested to the contacted server, it may return the following:
1747 SearchResultEntry for O=MNN,C=WW
1748 SearchResultEntry for CN=Manager,O=MNN,C=WW
1749 SearchResultReference {
1750 ldap://hostb/OU=People,O=MNN,C=WW
1751 ldap://hostc/OU=People,O=MNN,C=WW
1753 SearchResultReference {
1754 ldap://hostd/OU=Roles,O=MNN,C=WW
1756 SearchResultDone (success)
1758 Client implementors should note that when following a
1759 SearchResultReference, additional SearchResultReference may be
1760 generated. Continuing the example, if the client contacted the
1761 server (hostb) and issued the search for the subtree
1762 "OU=People,O=MNN,C=WW", the server might respond as follows:
1764 SearchResultEntry for OU=People,O=MNN,C=WW
1765 SearchResultReference {
1766 ldap://hoste/OU=Managers,OU=People,O=MNN,C=WW
1768 SearchResultReference {
1769 ldap://hostf/OU=Consultants,OU=People,O=MNN,C=WW
1771 SearchResultDone (success)
1773 If the contacted server does not hold the base object for the search,
1774 then it will return a referral to the client. For example, if the
1775 client requests a subtree search of "O=XYZ,C=US" to hosta, the server
1776 may return only a SearchResultDone containing a referral.
1778 SearchResultDone (referral) {
1782 4.6. Modify Operation
1784 The Modify Operation allows a client to request that a modification
1785 of an entry be performed on its behalf by a server. The Modify
1786 Request is defined as follows:
1788 ModifyRequest ::= [APPLICATION 6] SEQUENCE {
1790 modification SEQUENCE OF SEQUENCE {
1794 Wahl, et. al. Standards Track [Page 32]
1796 RFC 2251 LDAPv3 December 1997
1799 operation ENUMERATED {
1803 modification AttributeTypeAndValues } }
1805 AttributeTypeAndValues ::= SEQUENCE {
1806 type AttributeDescription,
1807 vals SET OF AttributeValue }
1809 Parameters of the Modify Request are:
1811 - object: The object to be modified. The value of this field contains
1812 the DN of the entry to be modified. The server will not perform
1813 any alias dereferencing in determining the object to be modified.
1815 - modification: A list of modifications to be performed on the entry.
1816 The entire list of entry modifications MUST be performed
1817 in the order they are listed, as a single atomic operation. While
1818 individual modifications may violate the directory schema, the
1819 resulting entry after the entire list of modifications is performed
1820 MUST conform to the requirements of the directory schema. The
1821 values that may be taken on by the 'operation' field in each
1822 modification construct have the following semantics respectively:
1824 add: add values listed to the given attribute, creating
1825 the attribute if necessary;
1827 delete: delete values listed from the given attribute,
1828 removing the entire attribute if no values are listed, or
1829 if all current values of the attribute are listed for
1832 replace: replace all existing values of the given attribute
1833 with the new values listed, creating the attribute if it
1834 did not already exist. A replace with no value will delete
1835 the entire attribute if it exists, and is ignored if the
1836 attribute does not exist.
1838 The result of the modify attempted by the server upon receipt of a
1839 Modify Request is returned in a Modify Response, defined as follows:
1841 ModifyResponse ::= [APPLICATION 7] LDAPResult
1843 Upon receipt of a Modify Request, a server will perform the necessary
1844 modifications to the DIT.
1850 Wahl, et. al. Standards Track [Page 33]
1852 RFC 2251 LDAPv3 December 1997
1855 The server will return to the client a single Modify Response
1856 indicating either the successful completion of the DIT modification,
1857 or the reason that the modification failed. Note that due to the
1858 requirement for atomicity in applying the list of modifications in
1859 the Modify Request, the client may expect that no modifications of
1860 the DIT have been performed if the Modify Response received indicates
1861 any sort of error, and that all requested modifications have been
1862 performed if the Modify Response indicates successful completion of
1863 the Modify Operation. If the connection fails, whether the
1864 modification occurred or not is indeterminate.
1866 The Modify Operation cannot be used to remove from an entry any of
1867 its distinguished values, those values which form the entry's
1868 relative distinguished name. An attempt to do so will result in the
1869 server returning the error notAllowedOnRDN. The Modify DN Operation
1870 described in section 4.9 is used to rename an entry.
1872 If an equality match filter has not been defined for an attribute type,
1873 clients MUST NOT attempt to delete individual values of that attribute
1874 from an entry using the "delete" form of a modification, and MUST
1875 instead use the "replace" form.
1877 Note that due to the simplifications made in LDAP, there is not a
1878 direct mapping of the modifications in an LDAP ModifyRequest onto the
1879 EntryModifications of a DAP ModifyEntry operation, and different
1880 implementations of LDAP-DAP gateways may use different means of
1881 representing the change. If successful, the final effect of the
1882 operations on the entry MUST be identical.
1886 The Add Operation allows a client to request the addition of an entry
1887 into the directory. The Add Request is defined as follows:
1889 AddRequest ::= [APPLICATION 8] SEQUENCE {
1891 attributes AttributeList }
1893 AttributeList ::= SEQUENCE OF SEQUENCE {
1894 type AttributeDescription,
1895 vals SET OF AttributeValue }
1897 Parameters of the Add Request are:
1899 - entry: the Distinguished Name of the entry to be added. Note that
1900 the server will not dereference any aliases in locating the entry
1906 Wahl, et. al. Standards Track [Page 34]
1908 RFC 2251 LDAPv3 December 1997
1911 - attributes: the list of attributes that make up the content of the
1912 entry being added. Clients MUST include distinguished values
1913 (those forming the entry's own RDN) in this list, the objectClass
1914 attribute, and values of any mandatory attributes of the listed
1915 object classes. Clients MUST NOT supply the createTimestamp or
1916 creatorsName attributes, since these will be generated
1917 automatically by the server.
1919 The entry named in the entry field of the AddRequest MUST NOT exist
1920 for the AddRequest to succeed. The parent of the entry to be added
1921 MUST exist. For example, if the client attempted to add
1922 "CN=JS,O=Foo,C=US", the "O=Foo,C=US" entry did not exist, and the
1923 "C=US" entry did exist, then the server would return the error
1924 noSuchObject with the matchedDN field containing "C=US". If the
1925 parent entry exists but is not in a naming context held by the
1926 server, the server SHOULD return a referral to the server holding the
1929 Servers implementations SHOULD NOT restrict where entries can be
1930 located in the directory. Some servers MAY allow the administrator
1931 to restrict the classes of entries which can be added to the
1934 Upon receipt of an Add Request, a server will attempt to perform the
1935 add requested. The result of the add attempt will be returned to the
1936 client in the Add Response, defined as follows:
1938 AddResponse ::= [APPLICATION 9] LDAPResult
1940 A response of success indicates that the new entry is present in the
1943 4.8. Delete Operation
1945 The Delete Operation allows a client to request the removal of an
1946 entry from the directory. The Delete Request is defined as follows:
1948 DelRequest ::= [APPLICATION 10] LDAPDN
1950 The Delete Request consists of the Distinguished Name of the entry to
1951 be deleted. Note that the server will not dereference aliases while
1952 resolving the name of the target entry to be removed, and that only
1953 leaf entries (those with no subordinate entries) can be deleted with
1956 The result of the delete attempted by the server upon receipt of a
1957 Delete Request is returned in the Delete Response, defined as
1962 Wahl, et. al. Standards Track [Page 35]
1964 RFC 2251 LDAPv3 December 1997
1967 DelResponse ::= [APPLICATION 11] LDAPResult
1969 Upon receipt of a Delete Request, a server will attempt to perform
1970 the entry removal requested. The result of the delete attempt will be
1971 returned to the client in the Delete Response.
1973 4.9. Modify DN Operation
1975 The Modify DN Operation allows a client to change the leftmost (least
1976 significant) component of the name of an entry in the directory, or
1977 to move a subtree of entries to a new location in the directory. The
1978 Modify DN Request is defined as follows:
1980 ModifyDNRequest ::= [APPLICATION 12] SEQUENCE {
1982 newrdn RelativeLDAPDN,
1983 deleteoldrdn BOOLEAN,
1984 newSuperior [0] LDAPDN OPTIONAL }
1986 Parameters of the Modify DN Request are:
1988 - entry: the Distinguished Name of the entry to be changed. This
1989 entry may or may not have subordinate entries.
1991 - newrdn: the RDN that will form the leftmost component of the new
1994 - deleteoldrdn: a boolean parameter that controls whether the old RDN
1995 attribute values are to be retained as attributes of the entry, or
1996 deleted from the entry.
1998 - newSuperior: if present, this is the Distinguished Name of the entry
1999 which becomes the immediate superior of the existing entry.
2001 The result of the name change attempted by the server upon receipt of
2002 a Modify DN Request is returned in the Modify DN Response, defined
2005 ModifyDNResponse ::= [APPLICATION 13] LDAPResult
2007 Upon receipt of a ModifyDNRequest, a server will attempt to
2008 perform the name change. The result of the name change attempt will
2009 be returned to the client in the Modify DN Response.
2011 For example, if the entry named in the "entry" parameter was
2012 "cn=John Smith,c=US", the newrdn parameter was "cn=John Cougar Smith",
2013 and the newSuperior parameter was absent, then this operation would
2018 Wahl, et. al. Standards Track [Page 36]
2020 RFC 2251 LDAPv3 December 1997
2023 attempt to rename the entry to be "cn=John Cougar Smith,c=US". If
2024 there was already an entry with that name, the operation would fail
2025 with error code entryAlreadyExists.
2027 If the deleteoldrdn parameter is TRUE, the values forming the old
2028 RDN are deleted from the entry. If the deleteoldrdn parameter is
2029 FALSE, the values forming the old RDN will be retained as
2030 non-distinguished attribute values of the entry. The server may
2031 not perform the operation and return an error code if the setting of
2032 the deleteoldrdn parameter would cause a schema inconsistency in the
2035 Note that X.500 restricts the ModifyDN operation to only affect
2036 entries that are contained within a single server. If the LDAP
2037 server is mapped onto DAP, then this restriction will apply, and the
2038 resultCode affectsMultipleDSAs will be returned if this error
2039 occurred. In general clients MUST NOT expect to be able to perform
2040 arbitrary movements of entries and subtrees between servers.
2042 4.10. Compare Operation
2044 The Compare Operation allows a client to compare an assertion
2045 provided with an entry in the directory. The Compare Request is
2048 CompareRequest ::= [APPLICATION 14] SEQUENCE {
2050 ava AttributeValueAssertion }
2052 Parameters of the Compare Request are:
2054 - entry: the name of the entry to be compared with.
2056 - ava: the assertion with which an attribute in the entry is to be
2059 The result of the compare attempted by the server upon receipt of a
2060 Compare Request is returned in the Compare Response, defined as
2063 CompareResponse ::= [APPLICATION 15] LDAPResult
2065 Upon receipt of a Compare Request, a server will attempt to perform
2066 the requested comparison. The result of the comparison will be
2067 returned to the client in the Compare Response. Note that errors and
2068 the result of comparison are all returned in the same construct.
2074 Wahl, et. al. Standards Track [Page 37]
2076 RFC 2251 LDAPv3 December 1997
2079 Note that some directory systems may establish access controls which
2080 permit the values of certain attributes (such as userPassword) to be
2081 compared but not read. In a search result, it may be that an
2082 attribute of that type would be returned, but with an empty set of
2085 4.11. Abandon Operation
2087 The function of the Abandon Operation is to allow a client to request
2088 that the server abandon an outstanding operation. The Abandon
2089 Request is defined as follows:
2091 AbandonRequest ::= [APPLICATION 16] MessageID
2093 The MessageID MUST be that of a an operation which was requested
2094 earlier in this connection.
2096 (The abandon request itself has its own message id. This is distinct
2097 from the id of the earlier operation being abandoned.)
2099 There is no response defined in the Abandon Operation. Upon
2100 transmission of an Abandon Operation, a client may expect that the
2101 operation identified by the Message ID in the Abandon Request has
2102 been abandoned. In the event that a server receives an Abandon
2103 Request on a Search Operation in the midst of transmitting responses
2104 to the search, that server MUST cease transmitting entry responses to
2105 the abandoned request immediately, and MUST NOT send the
2106 SearchResponseDone. Of course, the server MUST ensure that only
2107 properly encoded LDAPMessage PDUs are transmitted.
2109 Clients MUST NOT send abandon requests for the same operation
2110 multiple times, and MUST also be prepared to receive results from
2111 operations it has abandoned (since these may have been in transit
2112 when the abandon was requested).
2114 Servers MUST discard abandon requests for message IDs they do not
2115 recognize, for operations which cannot be abandoned, and for
2116 operations which have already been abandoned.
2118 4.12. Extended Operation
2120 An extension mechanism has been added in this version of LDAP, in
2121 order to allow additional operations to be defined for services not
2122 available elsewhere in this protocol, for instance digitally signed
2123 operations and results.
2130 Wahl, et. al. Standards Track [Page 38]
2132 RFC 2251 LDAPv3 December 1997
2135 The extended operation allows clients to make requests and receive
2136 responses with predefined syntaxes and semantics. These may be
2137 defined in RFCs or be private to particular implementations. Each
2138 request MUST have a unique OBJECT IDENTIFIER assigned to it.
2140 ExtendedRequest ::= [APPLICATION 23] SEQUENCE {
2141 requestName [0] LDAPOID,
2142 requestValue [1] OCTET STRING OPTIONAL }
2144 The requestName is a dotted-decimal representation of the OBJECT
2145 IDENTIFIER corresponding to the request. The requestValue is
2146 information in a form defined by that request, encapsulated inside an
2149 The server will respond to this with an LDAPMessage containing the
2152 ExtendedResponse ::= [APPLICATION 24] SEQUENCE {
2153 COMPONENTS OF LDAPResult,
2154 responseName [10] LDAPOID OPTIONAL,
2155 response [11] OCTET STRING OPTIONAL }
2157 If the server does not recognize the request name, it MUST return
2158 only the response fields from LDAPResult, containing the
2159 protocolError result code.
2161 5. Protocol Element Encodings and Transfer
2163 One underlying service is defined here. Clients and servers SHOULD
2164 implement the mapping of LDAP over TCP described in 5.2.1.
2166 5.1. Mapping Onto BER-based Transport Services
2168 The protocol elements of LDAP are encoded for exchange using the
2169 Basic Encoding Rules (BER) [11] of ASN.1 [3]. However, due to the
2170 high overhead involved in using certain elements of the BER, the
2171 following additional restrictions are placed on BER-encodings of LDAP
2174 (1) Only the definite form of length encoding will be used.
2176 (2) OCTET STRING values will be encoded in the primitive form only.
2178 (3) If the value of a BOOLEAN type is true, the encoding MUST have
2179 its contents octets set to hex "FF".
2186 Wahl, et. al. Standards Track [Page 39]
2188 RFC 2251 LDAPv3 December 1997
2191 (4) If a value of a type is its default value, it MUST be absent.
2192 Only some BOOLEAN and INTEGER types have default values in this
2193 protocol definition.
2195 These restrictions do not apply to ASN.1 types encapsulated inside of
2196 OCTET STRING values, such as attribute values, unless otherwise
2199 5.2. Transfer Protocols
2201 This protocol is designed to run over connection-oriented, reliable
2202 transports, with all 8 bits in an octet being significant in the data
2205 5.2.1. Transmission Control Protocol (TCP)
2207 The LDAPMessage PDUs are mapped directly onto the TCP bytestream. It
2208 is recommended that server implementations running over the TCP MAY
2209 provide a protocol listener on the assigned port, 389. Servers may
2210 instead provide a listener on a different port number. Clients MUST
2211 support contacting servers on any valid TCP port.
2213 6. Implementation Guidelines
2215 This document describes an Internet protocol.
2217 6.1. Server Implementations
2219 The server MUST be capable of recognizing all the mandatory attribute
2220 type names and implement the syntaxes specified in [5]. Servers MAY
2221 also recognize additional attribute type names.
2223 6.2. Client Implementations
2225 Clients which request referrals MUST ensure that they do not loop
2226 between servers. They MUST NOT repeatedly contact the same server for
2227 the same request with the same target entry name, scope and filter.
2228 Some clients may be using a counter that is incremented each time
2229 referral handling occurs for an operation, and these kinds of clients
2230 MUST be able to handle a DIT with at least ten layers of naming
2231 contexts between the root and a leaf entry.
2233 In the absence of prior agreements with servers, clients SHOULD NOT
2234 assume that servers support any particular schemas beyond those
2235 referenced in section 6.1. Different schemas can have different
2236 attribute types with the same names. The client can retrieve the
2237 subschema entries referenced by the subschemaSubentry attribute in
2238 the server's root DSE or in entries held by the server.
2242 Wahl, et. al. Standards Track [Page 40]
2244 RFC 2251 LDAPv3 December 1997
2247 7. Security Considerations
2249 When used with a connection-oriented transport, this version of the
2250 protocol provides facilities for the LDAP v2 authentication
2251 mechanism, simple authentication using a cleartext password, as well
2252 as any SASL mechanism [12]. SASL allows for integrity and privacy
2253 services to be negotiated.
2255 It is also permitted that the server can return its credentials to
2256 the client, if it chooses to do so.
2258 Use of cleartext password is strongly discouraged where the
2259 underlying transport service cannot guarantee confidentiality and may
2260 result in disclosure of the password to unauthorized parties.
2262 When used with SASL, it should be noted that the name field of the
2263 BindRequest is not protected against modification. Thus if the
2264 distinguished name of the client (an LDAPDN) is agreed through the
2265 negotiation of the credentials, it takes precedence over any value in
2266 the unprotected name field.
2268 Implementations which cache attributes and entries obtained via LDAP
2269 MUST ensure that access controls are maintained if that information
2270 is to be provided to multiple clients, since servers may have access
2271 control policies which prevent the return of entries or attributes in
2272 search results except to particular authenticated clients. For
2273 example, caches could serve result information only to the client
2274 whose request caused it to be cache.
2278 This document is an update to RFC 1777, by Wengyik Yeong, Tim Howes,
2279 and Steve Kille. Design ideas included in this document are based on
2280 those discussed in ASID and other IETF Working Groups. The
2281 contributions of individuals in these working groups is gratefully
2286 [1] ITU-T Rec. X.500, "The Directory: Overview of Concepts, Models
2289 [2] Yeong, W., Howes, T., and S. Kille, "Lightweight Directory Access
2290 Protocol", RFC 1777, March 1995.
2292 [3] ITU-T Rec. X.680, "Abstract Syntax Notation One (ASN.1) -
2293 Specification of Basic Notation", 1994.
2298 Wahl, et. al. Standards Track [Page 41]
2300 RFC 2251 LDAPv3 December 1997
2303 [4] Kille, S., Wahl, M., and T. Howes, "Lightweight Directory Access
2304 Protocol (v3): UTF-8 String Representation of Distinguished
2305 Names", RFC 2253, December 1997.
2307 [5] Wahl, M., Coulbeck, A., Howes, T., and S. Kille, "Lightweight
2308 Directory Access Protocol (v3): Attribute Syntax Definitions",
2309 RFC 2252, December 1997.
2311 [6] ITU-T Rec. X.501, "The Directory: Models", 1993.
2313 [7] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
2314 Resource Locators (URL)", RFC 1738, December 1994.
2316 [8] ITU-T Rec. X.511, "The Directory: Abstract Service Definition",
2319 [9] Howes, T., and M. Smith, "The LDAP URL Format", RFC 2255,
2322 [10] Bradner, S., "Key words for use in RFCs to Indicate Requirement
2323 Levels", RFC 2119, March 1997.
2325 [11] ITU-T Rec. X.690, "Specification of ASN.1 encoding rules: Basic,
2326 Canonical, and Distinguished Encoding Rules", 1994.
2328 [12] Meyers, J., "Simple Authentication and Security Layer",
2329 RFC 2222, October 1997.
2331 [13] Universal Multiple-Octet Coded Character Set (UCS) -
2332 Architecture and Basic Multilingual Plane, ISO/IEC 10646-1 :
2335 [14] Yergeau, F., "UTF-8, a transformation format of Unicode and ISO
2336 10646", RFC 2044, October 1996.
2338 10. Authors' Addresses
2342 4815 W Braker Lane #502-385
2346 Phone: +1 512 372-3160
2347 EMail: M.Wahl@critical-angle.com
2354 Wahl, et. al. Standards Track [Page 42]
2356 RFC 2251 LDAPv3 December 1997
2360 Netscape Communications Corp.
2361 501 E. Middlefield Rd., MS MV068
2362 Mountain View, CA 94043
2365 Phone: +1 650 937-3419
2366 EMail: howes@netscape.com
2370 The Dome, The Square
2375 Phone: +44-181-332-9091
2376 EMail: S.Kille@isode.com
2410 Wahl, et. al. Standards Track [Page 43]
2412 RFC 2251 LDAPv3 December 1997
2415 Appendix A - Complete ASN.1 Definition
2417 Lightweight-Directory-Access-Protocol-V3 DEFINITIONS
2422 LDAPMessage ::= SEQUENCE {
2423 messageID MessageID,
2425 bindRequest BindRequest,
2426 bindResponse BindResponse,
2427 unbindRequest UnbindRequest,
2428 searchRequest SearchRequest,
2429 searchResEntry SearchResultEntry,
2430 searchResDone SearchResultDone,
2431 searchResRef SearchResultReference,
2432 modifyRequest ModifyRequest,
2433 modifyResponse ModifyResponse,
2434 addRequest AddRequest,
2435 addResponse AddResponse,
2436 delRequest DelRequest,
2437 delResponse DelResponse,
2438 modDNRequest ModifyDNRequest,
2439 modDNResponse ModifyDNResponse,
2440 compareRequest CompareRequest,
2441 compareResponse CompareResponse,
2442 abandonRequest AbandonRequest,
2443 extendedReq ExtendedRequest,
2444 extendedResp ExtendedResponse },
2445 controls [0] Controls OPTIONAL }
2447 MessageID ::= INTEGER (0 .. maxInt)
2449 maxInt INTEGER ::= 2147483647 -- (2^^31 - 1) --
2451 LDAPString ::= OCTET STRING
2453 LDAPOID ::= OCTET STRING
2455 LDAPDN ::= LDAPString
2457 RelativeLDAPDN ::= LDAPString
2459 AttributeType ::= LDAPString
2461 AttributeDescription ::= LDAPString
2466 Wahl, et. al. Standards Track [Page 44]
2468 RFC 2251 LDAPv3 December 1997
2471 AttributeDescriptionList ::= SEQUENCE OF
2472 AttributeDescription
2474 AttributeValue ::= OCTET STRING
2476 AttributeValueAssertion ::= SEQUENCE {
2477 attributeDesc AttributeDescription,
2478 assertionValue AssertionValue }
2480 AssertionValue ::= OCTET STRING
2482 Attribute ::= SEQUENCE {
2483 type AttributeDescription,
2484 vals SET OF AttributeValue }
2486 MatchingRuleId ::= LDAPString
2488 LDAPResult ::= SEQUENCE {
2489 resultCode ENUMERATED {
2491 operationsError (1),
2493 timeLimitExceeded (3),
2494 sizeLimitExceeded (4),
2497 authMethodNotSupported (7),
2498 strongAuthRequired (8),
2500 referral (10), -- new
2501 adminLimitExceeded (11), -- new
2502 unavailableCriticalExtension (12), -- new
2503 confidentialityRequired (13), -- new
2504 saslBindInProgress (14), -- new
2505 noSuchAttribute (16),
2506 undefinedAttributeType (17),
2507 inappropriateMatching (18),
2508 constraintViolation (19),
2509 attributeOrValueExists (20),
2510 invalidAttributeSyntax (21),
2514 invalidDNSyntax (34),
2515 -- 35 reserved for undefined isLeaf --
2516 aliasDereferencingProblem (36),
2518 inappropriateAuthentication (48),
2522 Wahl, et. al. Standards Track [Page 45]
2524 RFC 2251 LDAPv3 December 1997
2527 invalidCredentials (49),
2528 insufficientAccessRights (50),
2531 unwillingToPerform (53),
2534 namingViolation (64),
2535 objectClassViolation (65),
2536 notAllowedOnNonLeaf (66),
2537 notAllowedOnRDN (67),
2538 entryAlreadyExists (68),
2539 objectClassModsProhibited (69),
2540 -- 70 reserved for CLDAP --
2541 affectsMultipleDSAs (71), -- new
2544 -- 81-90 reserved for APIs --
2546 errorMessage LDAPString,
2547 referral [3] Referral OPTIONAL }
2549 Referral ::= SEQUENCE OF LDAPURL
2551 LDAPURL ::= LDAPString -- limited to characters permitted in URLs
2553 Controls ::= SEQUENCE OF Control
2555 Control ::= SEQUENCE {
2556 controlType LDAPOID,
2557 criticality BOOLEAN DEFAULT FALSE,
2558 controlValue OCTET STRING OPTIONAL }
2560 BindRequest ::= [APPLICATION 0] SEQUENCE {
2561 version INTEGER (1 .. 127),
2563 authentication AuthenticationChoice }
2565 AuthenticationChoice ::= CHOICE {
2566 simple [0] OCTET STRING,
2568 sasl [3] SaslCredentials }
2570 SaslCredentials ::= SEQUENCE {
2571 mechanism LDAPString,
2572 credentials OCTET STRING OPTIONAL }
2574 BindResponse ::= [APPLICATION 1] SEQUENCE {
2578 Wahl, et. al. Standards Track [Page 46]
2580 RFC 2251 LDAPv3 December 1997
2583 COMPONENTS OF LDAPResult,
2584 serverSaslCreds [7] OCTET STRING OPTIONAL }
2586 UnbindRequest ::= [APPLICATION 2] NULL
2588 SearchRequest ::= [APPLICATION 3] SEQUENCE {
2594 derefAliases ENUMERATED {
2595 neverDerefAliases (0),
2596 derefInSearching (1),
2597 derefFindingBaseObj (2),
2599 sizeLimit INTEGER (0 .. maxInt),
2600 timeLimit INTEGER (0 .. maxInt),
2603 attributes AttributeDescriptionList }
2606 and [0] SET OF Filter,
2607 or [1] SET OF Filter,
2609 equalityMatch [3] AttributeValueAssertion,
2610 substrings [4] SubstringFilter,
2611 greaterOrEqual [5] AttributeValueAssertion,
2612 lessOrEqual [6] AttributeValueAssertion,
2613 present [7] AttributeDescription,
2614 approxMatch [8] AttributeValueAssertion,
2615 extensibleMatch [9] MatchingRuleAssertion }
2617 SubstringFilter ::= SEQUENCE {
2618 type AttributeDescription,
2619 -- at least one must be present
2620 substrings SEQUENCE OF CHOICE {
2621 initial [0] LDAPString,
2623 final [2] LDAPString } }
2625 MatchingRuleAssertion ::= SEQUENCE {
2626 matchingRule [1] MatchingRuleId OPTIONAL,
2627 type [2] AttributeDescription OPTIONAL,
2628 matchValue [3] AssertionValue,
2629 dnAttributes [4] BOOLEAN DEFAULT FALSE }
2634 Wahl, et. al. Standards Track [Page 47]
2636 RFC 2251 LDAPv3 December 1997
2639 SearchResultEntry ::= [APPLICATION 4] SEQUENCE {
2641 attributes PartialAttributeList }
2643 PartialAttributeList ::= SEQUENCE OF SEQUENCE {
2644 type AttributeDescription,
2645 vals SET OF AttributeValue }
2647 SearchResultReference ::= [APPLICATION 19] SEQUENCE OF LDAPURL
2649 SearchResultDone ::= [APPLICATION 5] LDAPResult
2651 ModifyRequest ::= [APPLICATION 6] SEQUENCE {
2653 modification SEQUENCE OF SEQUENCE {
2654 operation ENUMERATED {
2658 modification AttributeTypeAndValues } }
2660 AttributeTypeAndValues ::= SEQUENCE {
2661 type AttributeDescription,
2662 vals SET OF AttributeValue }
2664 ModifyResponse ::= [APPLICATION 7] LDAPResult
2666 AddRequest ::= [APPLICATION 8] SEQUENCE {
2668 attributes AttributeList }
2670 AttributeList ::= SEQUENCE OF SEQUENCE {
2671 type AttributeDescription,
2672 vals SET OF AttributeValue }
2674 AddResponse ::= [APPLICATION 9] LDAPResult
2676 DelRequest ::= [APPLICATION 10] LDAPDN
2678 DelResponse ::= [APPLICATION 11] LDAPResult
2680 ModifyDNRequest ::= [APPLICATION 12] SEQUENCE {
2682 newrdn RelativeLDAPDN,
2683 deleteoldrdn BOOLEAN,
2684 newSuperior [0] LDAPDN OPTIONAL }
2686 ModifyDNResponse ::= [APPLICATION 13] LDAPResult
2690 Wahl, et. al. Standards Track [Page 48]
2692 RFC 2251 LDAPv3 December 1997
2695 CompareRequest ::= [APPLICATION 14] SEQUENCE {
2697 ava AttributeValueAssertion }
2699 CompareResponse ::= [APPLICATION 15] LDAPResult
2701 AbandonRequest ::= [APPLICATION 16] MessageID
2703 ExtendedRequest ::= [APPLICATION 23] SEQUENCE {
2704 requestName [0] LDAPOID,
2705 requestValue [1] OCTET STRING OPTIONAL }
2707 ExtendedResponse ::= [APPLICATION 24] SEQUENCE {
2708 COMPONENTS OF LDAPResult,
2709 responseName [10] LDAPOID OPTIONAL,
2710 response [11] OCTET STRING OPTIONAL }
2746 Wahl, et. al. Standards Track [Page 49]
2748 RFC 2251 LDAPv3 December 1997
2751 Full Copyright Statement
2753 Copyright (C) The Internet Society (1997). All Rights Reserved.
2755 This document and translations of it may be copied and furnished to
2756 others, and derivative works that comment on or otherwise explain it
2757 or assist in its implementation may be prepared, copied, published
2758 and distributed, in whole or in part, without restriction of any
2759 kind, provided that the above copyright notice and this paragraph are
2760 included on all such copies and derivative works. However, this
2761 document itself may not be modified in any way, such as by removing
2762 the copyright notice or references to the Internet Society or other
2763 Internet organizations, except as needed for the purpose of
2764 developing Internet standards in which case the procedures for
2765 copyrights defined in the Internet Standards process must be
2766 followed, or as required to translate it into languages other than
2769 The limited permissions granted above are perpetual and will not be
2770 revoked by the Internet Society or its successors or assigns.
2772 This document and the information contained herein is provided on an
2773 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
2774 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
2775 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
2776 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
2777 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
2802 Wahl, et. al. Standards Track [Page 50]
projects / openldap / blob