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Network Working Group J. Sermersheim, Ed.
Request for Comments: 4511 Novell, Inc.
Obsoletes: 2251, 2830, 3771 June 2006
Category: Standards Track
Lightweight Directory Access Protocol (LDAP): The Protocol
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document describes the protocol elements, along with their
semantics and encodings, of the Lightweight Directory Access Protocol
(LDAP). LDAP provides access to distributed directory services that
act in accordance with X.500 data and service models. These protocol
elements are based on those described in the X.500 Directory Access
Protocol (DAP).
Table of Contents
1. Introduction ....................................................3
1.1. Relationship to Other LDAP Specifications ..................3
2. Conventions .....................................................3
3. Protocol Model ..................................................4
3.1. Operation and LDAP Message Layer Relationship ..............5
4. Elements of Protocol ............................................5
4.1. Common Elements ............................................5
4.1.1. Message Envelope ....................................6
4.1.2. String Types ........................................7
4.1.3. Distinguished Name and Relative Distinguished Name ..8
4.1.4. Attribute Descriptions ..............................8
4.1.5. Attribute Value .....................................8
4.1.6. Attribute Value Assertion ...........................9
4.1.7. Attribute and PartialAttribute ......................9
4.1.8. Matching Rule Identifier ...........................10
4.1.9. Result Message .....................................10
4.1.10. Referral ..........................................12
Sermersheim Standards Track [Page 1]
RFC 4511 LDAPv3 June 2006
4.1.11. Controls ..........................................14
4.2. Bind Operation ............................................16
4.2.1. Processing of the Bind Request .....................17
4.2.2. Bind Response ......................................18
4.3. Unbind Operation ..........................................18
4.4. Unsolicited Notification ..................................19
4.4.1. Notice of Disconnection ............................19
4.5. Search Operation ..........................................20
4.5.1. Search Request .....................................20
4.5.2. Search Result ......................................27
4.5.3. Continuation References in the Search Result .......28
4.6. Modify Operation ..........................................31
4.7. Add Operation .............................................33
4.8. Delete Operation ..........................................34
4.9. Modify DN Operation .......................................34
4.10. Compare Operation ........................................36
4.11. Abandon Operation ........................................36
4.12. Extended Operation .......................................37
4.13. IntermediateResponse Message .............................39
4.13.1. Usage with LDAP ExtendedRequest and
ExtendedResponse ..................................40
4.13.2. Usage with LDAP Request Controls ..................40
4.14. StartTLS Operation .......................................40
4.14.1. StartTLS Request ..................................40
4.14.2. StartTLS Response .................................41
4.14.3. Removal of the TLS Layer ..........................41
5. Protocol Encoding, Connection, and Transfer ....................42
5.1. Protocol Encoding .........................................42
5.2. Transmission Control Protocol (TCP) .......................43
5.3. Termination of the LDAP session ...........................43
6. Security Considerations ........................................43
7. Acknowledgements ...............................................45
8. Normative References ...........................................46
9. Informative References .........................................48
10. IANA Considerations ...........................................48
Appendix A. LDAP Result Codes .....................................49
A.1. Non-Error Result Codes ....................................49
A.2. Result Codes ..............................................49
Appendix B. Complete ASN.1 Definition .............................54
Appendix C. Changes ...............................................60
C.1. Changes Made to RFC 2251 ..................................60
C.2. Changes Made to RFC 2830 ..................................66
C.3. Changes Made to RFC 3771 ..................................66
Sermersheim Standards Track [Page 2]
RFC 4511 LDAPv3 June 2006
1. Introduction
The Directory is "a collection of open systems cooperating to provide
directory services" [X.500]. A directory user, which may be a human
or other entity, accesses the Directory through a client (or
Directory User Agent (DUA)). The client, on behalf of the directory
user, interacts with one or more servers (or Directory System Agents
(DSA)). Clients interact with servers using a directory access
protocol.
This document details the protocol elements of the Lightweight
Directory Access Protocol (LDAP), along with their semantics.
Following the description of protocol elements, it describes the way
in which the protocol elements are encoded and transferred.
1.1. Relationship to Other LDAP Specifications
This document is an integral part of the LDAP Technical Specification
[RFC4510], which obsoletes the previously defined LDAP technical
specification, RFC 3377, in its entirety.
This document, together with [RFC4510], [RFC4513], and [RFC4512],
obsoletes RFC 2251 in its entirety. Section 3.3 is obsoleted by
[RFC4510]. Sections 4.2.1 (portions) and 4.2.2 are obsoleted by
[RFC4513]. Sections 3.2, 3.4, 4.1.3 (last paragraph), 4.1.4, 4.1.5,
4.1.5.1, 4.1.9 (last paragraph), 5.1, 6.1, and 6.2 (last paragraph)
are obsoleted by [RFC4512]. The remainder of RFC 2251 is obsoleted
by this document. Appendix C.1 summarizes substantive changes in the
remainder.
This document obsoletes RFC 2830, Sections 2 and 4. The remainder of
RFC 2830 is obsoleted by [RFC4513]. Appendix C.2 summarizes
substantive changes to the remaining sections.
This document also obsoletes RFC 3771 in entirety.
2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", and "MAY" in this document are
to be interpreted as described in [RFC2119].
Character names in this document use the notation for code points and
names from the Unicode Standard [Unicode]. For example, the letter
"a" may be represented as either <U+0061> or <LATIN SMALL LETTER A>.
Sermersheim Standards Track [Page 3]
RFC 4511 LDAPv3 June 2006
Note: a glossary of terms used in Unicode can be found in [Glossary].
Information on the Unicode character encoding model can be found in
[CharModel].
The term "transport connection" refers to the underlying transport
services used to carry the protocol exchange, as well as associations
established by these services.
The term "TLS layer" refers to Transport Layer Security (TLS)
services used in providing security services, as well as associations
established by these services.
The term "SASL layer" refers to Simply Authentication and Security
Layer (SASL) services used in providing security services, as well as
associations established by these services.
The term "LDAP message layer" refers to the LDAP Message Protocol
Data Unit (PDU) services used in providing directory services, as
well as associations established by these services.
The term "LDAP session" refers to combined services (transport
connection, TLS layer, SASL layer, LDAP message layer) and their
associations.
See the table in Section 5 for an illustration of these four terms.
3. Protocol Model
The general model adopted by this protocol is one of clients
performing protocol operations against servers. In this model, a
client transmits a protocol request describing the operation to be
performed to a server. The server is then responsible for performing
the necessary operation(s) in the Directory. Upon completion of an
operation, the server typically returns a response containing
appropriate data to the requesting client.
Protocol operations are generally independent of one another. Each
operation is processed as an atomic action, leaving the directory in
a consistent state.
Although servers are required to return responses whenever such
responses are defined in the protocol, there is no requirement for
synchronous behavior on the part of either clients or servers.
Requests and responses for multiple operations generally may be
exchanged between a client and server in any order. If required,
synchronous behavior may be controlled by client applications.
Sermersheim Standards Track [Page 4]
RFC 4511 LDAPv3 June 2006
The core protocol operations defined in this document can be mapped
to a subset of the X.500 (1993) Directory Abstract Service [X.511].
However, there is not a one-to-one mapping between LDAP operations
and X.500 Directory Access Protocol (DAP) operations. Server
implementations acting as a gateway to X.500 directories may need to
make multiple DAP requests to service a single LDAP request.
3.1. Operation and LDAP Message Layer Relationship
Protocol operations are exchanged at the LDAP message layer. When
the transport connection is closed, any uncompleted operations at the
LDAP message layer are abandoned (when possible) or are completed
without transmission of the response (when abandoning them is not
possible). Also, when the transport connection is closed, the client
MUST NOT assume that any uncompleted update operations have succeeded
or failed.
4. Elements of Protocol
The protocol is described using Abstract Syntax Notation One
([ASN.1]) and is transferred using a subset of ASN.1 Basic Encoding
Rules ([BER]). Section 5 specifies how the protocol elements are
encoded and transferred.
In order to support future extensions to this protocol, extensibility
is implied where it is allowed per ASN.1 (i.e., sequence, set,
choice, and enumerated types are extensible). In addition, ellipses
(...) have been supplied in ASN.1 types that are explicitly
extensible as discussed in [RFC4520]. Because of the implied
extensibility, clients and servers MUST (unless otherwise specified)
ignore trailing SEQUENCE components whose tags they do not recognize.
Changes to the protocol other than through the extension mechanisms
described here require a different version number. A client
indicates the version it is using as part of the BindRequest,
described in Section 4.2. If a client has not sent a Bind, the
server MUST assume the client is using version 3 or later.
Clients may attempt to determine the protocol versions a server
supports by reading the 'supportedLDAPVersion' attribute from the
root DSE (DSA-Specific Entry) [RFC4512].
4.1. Common Elements
This section describes the LDAPMessage envelope Protocol Data Unit
(PDU) format, as well as data type definitions, which are used in the
protocol operations.
Sermersheim Standards Track [Page 5]
RFC 4511 LDAPv3 June 2006
4.1.1. Message Envelope
For the purposes of protocol exchanges, all protocol operations are
encapsulated in a common envelope, the LDAPMessage, which is defined
as follows:
LDAPMessage ::= SEQUENCE {
messageID MessageID,
protocolOp CHOICE {
bindRequest BindRequest,
bindResponse BindResponse,
unbindRequest UnbindRequest,
searchRequest SearchRequest,
searchResEntry SearchResultEntry,
searchResDone SearchResultDone,
searchResRef SearchResultReference,
modifyRequest ModifyRequest,
modifyResponse ModifyResponse,
addRequest AddRequest,
addResponse AddResponse,
delRequest DelRequest,
delResponse DelResponse,
modDNRequest ModifyDNRequest,
modDNResponse ModifyDNResponse,
compareRequest CompareRequest,
compareResponse CompareResponse,
abandonRequest AbandonRequest,
extendedReq ExtendedRequest,
extendedResp ExtendedResponse,
...,
intermediateResponse IntermediateResponse },
controls [0] Controls OPTIONAL }
MessageID ::= INTEGER (0 .. maxInt)
maxInt INTEGER ::= 2147483647 -- (2^^31 - 1) --
The ASN.1 type Controls is defined in Section 4.1.11.
The function of the LDAPMessage is to provide an envelope containing
common fields required in all protocol exchanges. At this time, the
only common fields are the messageID and the controls.
If the server receives an LDAPMessage from the client in which the
LDAPMessage SEQUENCE tag cannot be recognized, the messageID cannot
be parsed, the tag of the protocolOp is not recognized as a request,
or the encoding structures or lengths of data fields are found to be
incorrect, then the server SHOULD return the Notice of Disconnection
Sermersheim Standards Track [Page 6]
RFC 4511 LDAPv3 June 2006
described in Section 4.4.1, with the resultCode set to protocolError,
and MUST immediately terminate the LDAP session as described in
Section 5.3.
In other cases where the client or server cannot parse an LDAP PDU,
it SHOULD abruptly terminate the LDAP session (Section 5.3) where
further communication (including providing notice) would be
pernicious. Otherwise, server implementations MUST return an
appropriate response to the request, with the resultCode set to
protocolError.
4.1.1.1. MessageID
All LDAPMessage envelopes encapsulating responses contain the
messageID value of the corresponding request LDAPMessage.
The messageID of a request MUST have a non-zero value different from
the messageID of any other request in progress in the same LDAP
session. The zero value is reserved for the unsolicited notification
message.
Typical clients increment a counter for each request.
A client MUST NOT send a request with the same messageID as an
earlier request in the same LDAP session unless it can be determined
that the server is no longer servicing the earlier request (e.g.,
after the final response is received, or a subsequent Bind
completes). Otherwise, the behavior is undefined. For this purpose,
note that Abandon and successfully abandoned operations do not send
responses.
4.1.2. String Types
The LDAPString is a notational convenience to indicate that, although
strings of LDAPString type encode as ASN.1 OCTET STRING types, the
[ISO10646] character set (a superset of [Unicode]) is used, encoded
following the UTF-8 [RFC3629] algorithm. Note that Unicode
characters U+0000 through U+007F are the same as ASCII 0 through 127,
respectively, and have the same single octet UTF-8 encoding. Other
Unicode characters have a multiple octet UTF-8 encoding.
LDAPString ::= OCTET STRING -- UTF-8 encoded,
-- [ISO10646] characters
The LDAPOID is a notational convenience to indicate that the
permitted value of this string is a (UTF-8 encoded) dotted-decimal
representation of an OBJECT IDENTIFIER. Although an LDAPOID is
Sermersheim Standards Track [Page 7]
RFC 4511 LDAPv3 June 2006
encoded as an OCTET STRING, values are limited to the definition of
<numericoid> given in Section 1.4 of [RFC4512].
LDAPOID ::= OCTET STRING -- Constrained to <numericoid>
-- [RFC4512]
For example,
1.3.6.1.4.1.1466.1.2.3
4.1.3. Distinguished Name and Relative Distinguished Name
An LDAPDN is defined to be the representation of a Distinguished Name
(DN) after encoding according to the specification in [RFC4514].
LDAPDN ::= LDAPString
-- Constrained to <distinguishedName> [RFC4514]
A RelativeLDAPDN is defined to be the representation of a Relative
Distinguished Name (RDN) after encoding according to the
specification in [RFC4514].
RelativeLDAPDN ::= LDAPString
-- Constrained to <name-component> [RFC4514]
4.1.4. Attribute Descriptions
The definition and encoding rules for attribute descriptions are
defined in Section 2.5 of [RFC4512]. Briefly, an attribute
description is an attribute type and zero or more options.
AttributeDescription ::= LDAPString
-- Constrained to <attributedescription>
-- [RFC4512]
4.1.5. Attribute Value
A field of type AttributeValue is an OCTET STRING containing an
encoded attribute value. The attribute value is encoded according to
the LDAP-specific encoding definition of its corresponding syntax.
The LDAP-specific encoding definitions for different syntaxes and
attribute types may be found in other documents and in particular
[RFC4517].
AttributeValue ::= OCTET STRING
Sermersheim Standards Track [Page 8]
RFC 4511 LDAPv3 June 2006
Note that there is no defined limit on the size of this encoding;
thus, protocol values may include multi-megabyte attribute values
(e.g., photographs).
Attribute values may be defined that have arbitrary and non-printable
syntax. Implementations MUST NOT display or attempt to decode an
attribute value if its syntax is not known. The implementation may
attempt to discover the subschema of the source entry and to retrieve
the descriptions of 'attributeTypes' from it [RFC4512].
Clients MUST only send attribute values in a request that are valid
according to the syntax defined for the attributes.
4.1.6. Attribute Value Assertion
The AttributeValueAssertion (AVA) type definition is similar to the
one in the X.500 Directory standards. It contains an attribute
description and a matching rule ([RFC4512], Section 4.1.3) assertion
value suitable for that type. Elements of this type are typically
used to assert that the value in assertionValue matches a value of an
attribute.
AttributeValueAssertion ::= SEQUENCE {
attributeDesc AttributeDescription,
assertionValue AssertionValue }
AssertionValue ::= OCTET STRING
The syntax of the AssertionValue depends on the context of the LDAP
operation being performed. For example, the syntax of the EQUALITY
matching rule for an attribute is used when performing a Compare
operation. Often this is the same syntax used for values of the
attribute type, but in some cases the assertion syntax differs from
the value syntax. See objectIdentiferFirstComponentMatch in
[RFC4517] for an example.
4.1.7. Attribute and PartialAttribute
Attributes and partial attributes consist of an attribute description
and attribute values. A PartialAttribute allows zero values, while
Attribute requires at least one value.
PartialAttribute ::= SEQUENCE {
type AttributeDescription,
vals SET OF value AttributeValue }
Sermersheim Standards Track [Page 9]
RFC 4511 LDAPv3 June 2006
Attribute ::= PartialAttribute(WITH COMPONENTS {
...,
vals (SIZE(1..MAX))})
No two of the attribute values may be equivalent as described by
Section 2.2 of [RFC4512]. The set of attribute values is unordered.
Implementations MUST NOT rely upon the ordering being repeatable.
4.1.8. Matching Rule Identifier
Matching rules are defined in Section 4.1.3 of [RFC4512]. A matching
rule is identified in the protocol by the printable representation of
either its <numericoid> or one of its short name descriptors
[RFC4512], e.g., 'caseIgnoreMatch' or '2.5.13.2'.
MatchingRuleId ::= LDAPString
4.1.9. Result Message
The LDAPResult is the construct used in this protocol to return
success or failure indications from servers to clients. To various
requests, servers will return responses containing the elements found
in LDAPResult to indicate the final status of the protocol operation
request.
LDAPResult ::= SEQUENCE {
resultCode ENUMERATED {
success (0),
operationsError (1),
protocolError (2),
timeLimitExceeded (3),
sizeLimitExceeded (4),
compareFalse (5),
compareTrue (6),
authMethodNotSupported (7),
strongerAuthRequired (8),
-- 9 reserved --
referral (10),
adminLimitExceeded (11),
unavailableCriticalExtension (12),
confidentialityRequired (13),
saslBindInProgress (14),
noSuchAttribute (16),
undefinedAttributeType (17),
inappropriateMatching (18),
constraintViolation (19),
attributeOrValueExists (20),
invalidAttributeSyntax (21),
Sermersheim Standards Track [Page 10]
RFC 4511 LDAPv3 June 2006
-- 22-31 unused --
noSuchObject (32),
aliasProblem (33),
invalidDNSyntax (34),
-- 35 reserved for undefined isLeaf --
aliasDereferencingProblem (36),
-- 37-47 unused --
inappropriateAuthentication (48),
invalidCredentials (49),
insufficientAccessRights (50),
busy (51),
unavailable (52),
unwillingToPerform (53),
loopDetect (54),
-- 55-63 unused --
namingViolation (64),
objectClassViolation (65),
notAllowedOnNonLeaf (66),
notAllowedOnRDN (67),
entryAlreadyExists (68),
objectClassModsProhibited (69),
-- 70 reserved for CLDAP --
affectsMultipleDSAs (71),
-- 72-79 unused --
other (80),
... },
matchedDN LDAPDN,
diagnosticMessage LDAPString,
referral [3] Referral OPTIONAL }
The resultCode enumeration is extensible as defined in Section 3.8 of
[RFC4520]. The meanings of the listed result codes are given in
Appendix A. If a server detects multiple errors for an operation,
only one result code is returned. The server should return the
result code that best indicates the nature of the error encountered.
Servers may return substituted result codes to prevent unauthorized
disclosures.
The diagnosticMessage field of this construct may, at the server's
option, be used to return a string containing a textual, human-
readable diagnostic message (terminal control and page formatting
characters should be avoided). As this diagnostic message is not
standardized, implementations MUST NOT rely on the values returned.
Diagnostic messages typically supplement the resultCode with
additional information. If the server chooses not to return a
textual diagnostic, the diagnosticMessage field MUST be empty.
Sermersheim Standards Track [Page 11]
RFC 4511 LDAPv3 June 2006
For certain result codes (typically, but not restricted to
noSuchObject, aliasProblem, invalidDNSyntax, and
aliasDereferencingProblem), the matchedDN field is set (subject to
access controls) to the name of the last entry (object or alias) used
in finding the target (or base) object. This will be a truncated
form of the provided name or, if an alias was dereferenced while
attempting to locate the entry, of the resulting name. Otherwise,
the matchedDN field is empty.
4.1.10. Referral
The referral result code indicates that the contacted server cannot
or will not perform the operation and that one or more other servers
may be able to. Reasons for this include:
- The target entry of the request is not held locally, but the server
has knowledge of its possible existence elsewhere.
- The operation is restricted on this server -- perhaps due to a
read-only copy of an entry to be modified.
The referral field is present in an LDAPResult if the resultCode is
set to referral, and it is absent with all other result codes. It
contains one or more references to one or more servers or services
that may be accessed via LDAP or other protocols. Referrals can be
returned in response to any operation request (except Unbind and
Abandon, which do not have responses). At least one URI MUST be
present in the Referral.
During a Search operation, after the baseObject is located, and
entries are being evaluated, the referral is not returned. Instead,
continuation references, described in Section 4.5.3, are returned
when other servers would need to be contacted to complete the
operation.
Referral ::= SEQUENCE SIZE (1..MAX) OF uri URI
URI ::= LDAPString -- limited to characters permitted in
-- URIs
If the client wishes to progress the operation, it contacts one of
the supported services found in the referral. If multiple URIs are
present, the client assumes that any supported URI may be used to
progress the operation.
Clients that follow referrals MUST ensure that they do not loop
between servers. They MUST NOT repeatedly contact the same server
for the same request with the same parameters. Some clients use a
Sermersheim Standards Track [Page 12]
RFC 4511 LDAPv3 June 2006
counter that is incremented each time referral handling occurs for an
operation, and these kinds of clients MUST be able to handle at least
ten nested referrals while progressing the operation.
A URI for a server implementing LDAP and accessible via TCP/IP (v4 or
v6) [RFC793][RFC791] is written as an LDAP URL according to
[RFC4516].
Referral values that are LDAP URLs follow these rules:
- If an alias was dereferenced, the <dn> part of the LDAP URL MUST be
present, with the new target object name.
- It is RECOMMENDED that the <dn> part be present to avoid ambiguity.
- If the <dn> part is present, the client uses this name in its next
request to progress the operation, and if it is not present the
client uses the same name as in the original request.
- Some servers (e.g., participating in distributed indexing) may
provide a different filter in a URL of a referral for a Search
operation.
- If the <filter> part of the LDAP URL is present, the client uses
this filter in its next request to progress this Search, and if it
is not present the client uses the same filter as it used for that
Search.
- For Search, it is RECOMMENDED that the <scope> part be present to
avoid ambiguity.
- If the <scope> part is missing, the scope of the original Search is
used by the client to progress the operation.
- Other aspects of the new request may be the same as or different
from the request that generated the referral.
Other kinds of URIs may be returned. The syntax and semantics of
such URIs is left to future specifications. Clients may ignore URIs
that they do not support.
UTF-8 encoded characters appearing in the string representation of a
DN, search filter, or other fields of the referral value may not be
legal for URIs (e.g., spaces) and MUST be escaped using the % method
in [RFC3986].
Sermersheim Standards Track [Page 13]
RFC 4511 LDAPv3 June 2006
4.1.11. Controls
Controls provide a mechanism whereby the semantics and arguments of
existing LDAP operations may be extended. One or more controls may
be attached to a single LDAP message. A control only affects the
semantics of the message it is attached to.
Controls sent by clients are termed 'request controls', and those
sent by servers are termed 'response controls'.
Controls ::= SEQUENCE OF control Control
Control ::= SEQUENCE {
controlType LDAPOID,
criticality BOOLEAN DEFAULT FALSE,
controlValue OCTET STRING OPTIONAL }
The controlType field is the dotted-decimal representation of an
OBJECT IDENTIFIER that uniquely identifies the control. This
provides unambiguous naming of controls. Often, response control(s)
solicited by a request control share controlType values with the
request control.
The criticality field only has meaning in controls attached to
request messages (except UnbindRequest). For controls attached to
response messages and the UnbindRequest, the criticality field SHOULD
be FALSE, and MUST be ignored by the receiving protocol peer. A
value of TRUE indicates that it is unacceptable to perform the
operation without applying the semantics of the control.
Specifically, the criticality field is applied as follows:
- If the server does not recognize the control type, determines that
it is not appropriate for the operation, or is otherwise unwilling
to perform the operation with the control, and if the criticality
field is TRUE, the server MUST NOT perform the operation, and for
operations that have a response message, it MUST return with the
resultCode set to unavailableCriticalExtension.
- If the server does not recognize the control type, determines that
it is not appropriate for the operation, or is otherwise unwilling
to perform the operation with the control, and if the criticality
field is FALSE, the server MUST ignore the control.
- Regardless of criticality, if a control is applied to an
operation, it is applied consistently and impartially to the
entire operation.
Sermersheim Standards Track [Page 14]
RFC 4511 LDAPv3 June 2006
The controlValue may contain information associated with the
controlType. Its format is defined by the specification of the
control. Implementations MUST be prepared to handle arbitrary
contents of the controlValue octet string, including zero bytes. It
is absent only if there is no value information that is associated
with a control of its type. When a controlValue is defined in terms
of ASN.1, and BER-encoded according to Section 5.1, it also follows
the extensibility rules in Section 4.
Servers list the controlType of request controls they recognize in
the 'supportedControl' attribute in the root DSE (Section 5.1 of
[RFC4512]).
Controls SHOULD NOT be combined unless the semantics of the
combination has been specified. The semantics of control
combinations, if specified, are generally found in the control
specification most recently published. When a combination of
controls is encountered whose semantics are invalid, not specified
(or not known), the message is considered not well-formed; thus, the
operation fails with protocolError. Controls with a criticality of
FALSE may be ignored in order to arrive at a valid combination.
Additionally, unless order-dependent semantics are given in a
specification, the order of a combination of controls in the SEQUENCE
is ignored. Where the order is to be ignored but cannot be ignored
by the server, the message is considered not well-formed, and the
operation fails with protocolError. Again, controls with a
criticality of FALSE may be ignored in order to arrive at a valid
combination.
This document does not specify any controls. Controls may be
specified in other documents. Documents detailing control extensions
are to provide for each control:
- the OBJECT IDENTIFIER assigned to the control,
- direction as to what value the sender should provide for the
criticality field (note: the semantics of the criticality field are
defined above should not be altered by the control's
specification),
- whether the controlValue field is present, and if so, the format of
its contents,
- the semantics of the control, and
- optionally, semantics regarding the combination of the control with
other controls.
Sermersheim Standards Track [Page 15]
RFC 4511 LDAPv3 June 2006
4.2. Bind Operation
The function of the Bind operation is to allow authentication
information to be exchanged between the client and server. The Bind
operation should be thought of as the "authenticate" operation.
Operational, authentication, and security-related semantics of this
operation are given in [RFC4513].
The Bind request is defined as follows:
BindRequest ::= [APPLICATION 0] SEQUENCE {
version INTEGER (1 .. 127),
name LDAPDN,
authentication AuthenticationChoice }
AuthenticationChoice ::= CHOICE {
simple [0] OCTET STRING,
-- 1 and 2 reserved
sasl [3] SaslCredentials,
... }
SaslCredentials ::= SEQUENCE {
mechanism LDAPString,
credentials OCTET STRING OPTIONAL }
Fields of the BindRequest are:
- version: A version number indicating the version of the protocol to
be used at the LDAP message layer. This document describes version
3 of the protocol. There is no version negotiation. The client
sets this field to the version it desires. If the server does not
support the specified version, it MUST respond with a BindResponse
where the resultCode is set to protocolError.
- name: If not empty, the name of the Directory object that the
client wishes to bind as. This field may take on a null value (a
zero-length string) for the purposes of anonymous binds ([RFC4513],
Section 5.1) or when using SASL [RFC4422] authentication
([RFC4513], Section 5.2). Where the server attempts to locate the
named object, it SHALL NOT perform alias dereferencing.
- authentication: Information used in authentication. This type is
extensible as defined in Section 3.7 of [RFC4520]. Servers that do
not support a choice supplied by a client return a BindResponse
with the resultCode set to authMethodNotSupported.
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Textual passwords (consisting of a character sequence with a known
character set and encoding) transferred to the server using the
simple AuthenticationChoice SHALL be transferred as UTF-8 [RFC3629]
encoded [Unicode]. Prior to transfer, clients SHOULD prepare text
passwords as "query" strings by applying the SASLprep [RFC4013]
profile of the stringprep [RFC3454] algorithm. Passwords
consisting of other data (such as random octets) MUST NOT be
altered. The determination of whether a password is textual is a
local client matter.
4.2.1. Processing of the Bind Request
Before processing a BindRequest, all uncompleted operations MUST
either complete or be abandoned. The server may either wait for the
uncompleted operations to complete, or abandon them. The server then
proceeds to authenticate the client in either a single-step or
multi-step Bind process. Each step requires the server to return a
BindResponse to indicate the status of authentication.
After sending a BindRequest, clients MUST NOT send further LDAP PDUs
until receiving the BindResponse. Similarly, servers SHOULD NOT
process or respond to requests received while processing a
BindRequest.
If the client did not bind before sending a request and receives an
operationsError to that request, it may then send a BindRequest. If
this also fails or the client chooses not to bind on the existing
LDAP session, it may terminate the LDAP session, re-establish it, and
begin again by first sending a BindRequest. This will aid in
interoperating with servers implementing other versions of LDAP.
Clients may send multiple Bind requests to change the authentication
and/or security associations or to complete a multi-stage Bind
process. Authentication from earlier binds is subsequently ignored.
For some SASL authentication mechanisms, it may be necessary for the
client to invoke the BindRequest multiple times ([RFC4513], Section
5.2). Clients MUST NOT invoke operations between two Bind requests
made as part of a multi-stage Bind.
A client may abort a SASL bind negotiation by sending a BindRequest
with a different value in the mechanism field of SaslCredentials, or
an AuthenticationChoice other than sasl.
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If the client sends a BindRequest with the sasl mechanism field as an
empty string, the server MUST return a BindResponse with the
resultCode set to authMethodNotSupported. This will allow the client
to abort a negotiation if it wishes to try again with the same SASL
mechanism.
4.2.2. Bind Response
The Bind response is defined as follows.
BindResponse ::= [APPLICATION 1] SEQUENCE {
COMPONENTS OF LDAPResult,
serverSaslCreds [7] OCTET STRING OPTIONAL }
BindResponse consists simply of an indication from the server of the
status of the client's request for authentication.
A successful Bind operation is indicated by a BindResponse with a
resultCode set to success. Otherwise, an appropriate result code is
set in the BindResponse. For BindResponse, the protocolError result
code may be used to indicate that the version number supplied by the
client is unsupported.
If the client receives a BindResponse where the resultCode is set to
protocolError, it is to assume that the server does not support this
version of LDAP. While the client may be able proceed with another
version of this protocol (which may or may not require closing and
re-establishing the transport connection), how to proceed with
another version of this protocol is beyond the scope of this
document. Clients that are unable or unwilling to proceed SHOULD
terminate the LDAP session.
The serverSaslCreds field is used as part of a SASL-defined bind
mechanism to allow the client to authenticate the server to which it
is communicating, or to perform "challenge-response" authentication.
If the client bound with the simple choice, or the SASL mechanism
does not require the server to return information to the client, then
this field SHALL NOT be included in the BindResponse.
4.3. Unbind Operation
The function of the Unbind operation is to terminate an LDAP session.
The Unbind operation is not the antithesis of the Bind operation as
the name implies. The naming of these operations are historical.
The Unbind operation should be thought of as the "quit" operation.
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The Unbind operation is defined as follows:
UnbindRequest ::= [APPLICATION 2] NULL
The client, upon transmission of the UnbindRequest, and the server,
upon receipt of the UnbindRequest, are to gracefully terminate the
LDAP session as described in Section 5.3. Uncompleted operations are
handled as specified in Section 3.1.
4.4. Unsolicited Notification
An unsolicited notification is an LDAPMessage sent from the server to
the client that is not in response to any LDAPMessage received by the
server. It is used to signal an extraordinary condition in the
server or in the LDAP session between the client and the server. The
notification is of an advisory nature, and the server will not expect
any response to be returned from the client.
The unsolicited notification is structured as an LDAPMessage in which
the messageID is zero and protocolOp is set to the extendedResp
choice using the ExtendedResponse type (See Section 4.12). The
responseName field of the ExtendedResponse always contains an LDAPOID
that is unique for this notification.
One unsolicited notification (Notice of Disconnection) is defined in
this document. The specification of an unsolicited notification
consists of:
- the OBJECT IDENTIFIER assigned to the notification (to be specified
in the responseName,
- the format of the contents of the responseValue (if any),
- the circumstances which will cause the notification to be sent, and
- the semantics of the message.
4.4.1. Notice of Disconnection
This notification may be used by the server to advise the client that
the server is about to terminate the LDAP session on its own
initiative. This notification is intended to assist clients in
distinguishing between an exceptional server condition and a
transient network failure. Note that this notification is not a
response to an Unbind requested by the client. Uncompleted
operations are handled as specified in Section 3.1.
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The responseName is 1.3.6.1.4.1.1466.20036, the responseValue field
is absent, and the resultCode is used to indicate the reason for the
disconnection. When the strongerAuthRequired resultCode is returned
with this message, it indicates that the server has detected that an
established security association between the client and server has
unexpectedly failed or been compromised.
Upon transmission of the Notice of Disconnection, the server
gracefully terminates the LDAP session as described in Section 5.3.
4.5. Search Operation
The Search operation is used to request a server to return, subject
to access controls and other restrictions, a set of entries matching
a complex search criterion. This can be used to read attributes from
a single entry, from entries immediately subordinate to a particular
entry, or from a whole subtree of entries.
4.5.1. Search Request
The Search request is defined as follows:
SearchRequest ::= [APPLICATION 3] SEQUENCE {
baseObject LDAPDN,
scope ENUMERATED {
baseObject (0),
singleLevel (1),
wholeSubtree (2),
... },
derefAliases ENUMERATED {
neverDerefAliases (0),
derefInSearching (1),
derefFindingBaseObj (2),
derefAlways (3) },
sizeLimit INTEGER (0 .. maxInt),
timeLimit INTEGER (0 .. maxInt),
typesOnly BOOLEAN,
filter Filter,
attributes AttributeSelection }
AttributeSelection ::= SEQUENCE OF selector LDAPString
-- The LDAPString is constrained to
-- <attributeSelector> in Section 4.5.1.8
Filter ::= CHOICE {
and [0] SET SIZE (1..MAX) OF filter Filter,
or [1] SET SIZE (1..MAX) OF filter Filter,
not [2] Filter,
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equalityMatch [3] AttributeValueAssertion,
substrings [4] SubstringFilter,
greaterOrEqual [5] AttributeValueAssertion,
lessOrEqual [6] AttributeValueAssertion,
present [7] AttributeDescription,
approxMatch [8] AttributeValueAssertion,
extensibleMatch [9] MatchingRuleAssertion,
... }
SubstringFilter ::= SEQUENCE {
type AttributeDescription,
substrings SEQUENCE SIZE (1..MAX) OF substring CHOICE {
initial [0] AssertionValue, -- can occur at most once
any [1] AssertionValue,
final [2] AssertionValue } -- can occur at most once
}
MatchingRuleAssertion ::= SEQUENCE {
matchingRule [1] MatchingRuleId OPTIONAL,
type [2] AttributeDescription OPTIONAL,
matchValue [3] AssertionValue,
dnAttributes [4] BOOLEAN DEFAULT FALSE }
Note that an X.500 "list"-like operation can be emulated by the
client requesting a singleLevel Search operation with a filter
checking for the presence of the 'objectClass' attribute, and that an
X.500 "read"-like operation can be emulated by a baseObject Search
operation with the same filter. A server that provides a gateway to
X.500 is not required to use the Read or List operations, although it
may choose to do so, and if it does, it must provide the same
semantics as the X.500 Search operation.
4.5.1.1. SearchRequest.baseObject
The name of the base object entry (or possibly the root) relative to
which the Search is to be performed.
4.5.1.2. SearchRequest.scope
Specifies the scope of the Search to be performed. The semantics (as
described in [X.511]) of the defined values of this field are:
baseObject: The scope is constrained to the entry named by
baseObject.
singleLevel: The scope is constrained to the immediate
subordinates of the entry named by baseObject.
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wholeSubtree: The scope is constrained to the entry named by
baseObject and to all its subordinates.
4.5.1.3. SearchRequest.derefAliases
An indicator as to whether or not alias entries (as defined in
[RFC4512]) are to be dereferenced during stages of the Search
operation.
The act of dereferencing an alias includes recursively dereferencing
aliases that refer to aliases.
Servers MUST detect looping while dereferencing aliases in order to
prevent denial-of-service attacks of this nature.
The semantics of the defined values of this field are:
neverDerefAliases: Do not dereference aliases in searching or in
locating the base object of the Search.
derefInSearching: While searching subordinates of the base object,
dereference any alias within the search scope. Dereferenced
objects become the vertices of further search scopes where the
Search operation is also applied. If the search scope is
wholeSubtree, the Search continues in the subtree(s) of any
dereferenced object. If the search scope is singleLevel, the
search is applied to any dereferenced objects and is not applied
to their subordinates. Servers SHOULD eliminate duplicate entries
that arise due to alias dereferencing while searching.
derefFindingBaseObj: Dereference aliases in locating the base
object of the Search, but not when searching subordinates of the
base object.
derefAlways: Dereference aliases both in searching and in locating
the base object of the Search.
4.5.1.4. SearchRequest.sizeLimit
A size limit that restricts the maximum number of entries to be
returned as a result of the Search. A value of zero in this field
indicates that no client-requested size limit restrictions are in
effect for the Search. Servers may also enforce a maximum number of
entries to return.
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4.5.1.5. SearchRequest.timeLimit
A time limit that restricts the maximum time (in seconds) allowed for
a Search. A value of zero in this field indicates that no client-
requested time limit restrictions are in effect for the Search.
Servers may also enforce a maximum time limit for the Search.
4.5.1.6. SearchRequest.typesOnly
An indicator as to whether Search results are to contain both
attribute descriptions and values, or just attribute descriptions.
Setting this field to TRUE causes only attribute descriptions (and
not values) to be returned. Setting this field to FALSE causes both
attribute descriptions and values to be returned.
4.5.1.7. SearchRequest.filter
A filter that defines the conditions that must be fulfilled in order
for the Search to match a given entry.
The 'and', 'or', and 'not' choices can be used to form combinations
of filters. At least one filter element MUST be present in an 'and'
or 'or' choice. The others match against individual attribute values
of entries in the scope of the Search. (Implementor's note: the
'not' filter is an example of a tagged choice in an implicitly-tagged
module. In BER this is treated as if the tag were explicit.)
A server MUST evaluate filters according to the three-valued logic of
[X.511] (1993), Clause 7.8.1. In summary, a filter is evaluated to
"TRUE", "FALSE", or "Undefined". If the filter evaluates to TRUE for
a particular entry, then the attributes of that entry are returned as
part of the Search result (subject to any applicable access control
restrictions). If the filter evaluates to FALSE or Undefined, then
the entry is ignored for the Search.
A filter of the "and" choice is TRUE if all the filters in the SET OF
evaluate to TRUE, FALSE if at least one filter is FALSE, and
Undefined otherwise. A filter of the "or" choice is FALSE if all the
filters in the SET OF evaluate to FALSE, TRUE if at least one filter
is TRUE, and Undefined otherwise. A filter of the 'not' choice is
TRUE if the filter being negated is FALSE, FALSE if it is TRUE, and
Undefined if it is Undefined.
A filter item evaluates to Undefined when the server would not be
able to determine whether the assertion value matches an entry.
Examples include:
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- An attribute description in an equalityMatch, substrings,
greaterOrEqual, lessOrEqual, approxMatch, or extensibleMatch filter
is not recognized by the server.
- The attribute type does not define the appropriate matching rule.
- A MatchingRuleId in the extensibleMatch is not recognized by the
server or is not valid for the attribute type.
- The type of filtering requested is not implemented.
- The assertion value is invalid.
For example, if a server did not recognize the attribute type
shoeSize, the filters (shoeSize=*), (shoeSize=12), (shoeSize>=12),
and (shoeSize<=12) would each evaluate to Undefined.
Servers MUST NOT return errors if attribute descriptions or matching
rule ids are not recognized, assertion values are invalid, or the
assertion syntax is not supported. More details of filter processing
are given in Clause 7.8 of [X.511].
4.5.1.7.1. SearchRequest.filter.equalityMatch
The matching rule for an equalityMatch filter is defined by the
EQUALITY matching rule for the attribute type or subtype. The filter
is TRUE when the EQUALITY rule returns TRUE as applied to the
attribute or subtype and the asserted value.
4.5.1.7.2. SearchRequest.filter.substrings
There SHALL be at most one 'initial' and at most one 'final' in the
'substrings' of a SubstringFilter. If 'initial' is present, it SHALL
be the first element of 'substrings'. If 'final' is present, it
SHALL be the last element of 'substrings'.
The matching rule for an AssertionValue in a substrings filter item
is defined by the SUBSTR matching rule for the attribute type or
subtype. The filter is TRUE when the SUBSTR rule returns TRUE as
applied to the attribute or subtype and the asserted value.
Note that the AssertionValue in a substrings filter item conforms to
the assertion syntax of the EQUALITY matching rule for the attribute
type rather than to the assertion syntax of the SUBSTR matching rule
for the attribute type. Conceptually, the entire SubstringFilter is
converted into an assertion value of the substrings matching rule
prior to applying the rule.
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4.5.1.7.3. SearchRequest.filter.greaterOrEqual
The matching rule for a greaterOrEqual filter is defined by the
ORDERING matching rule for the attribute type or subtype. The filter
is TRUE when the ORDERING rule returns FALSE as applied to the
attribute or subtype and the asserted value.
4.5.1.7.4. SearchRequest.filter.lessOrEqual
The matching rules for a lessOrEqual filter are defined by the
ORDERING and EQUALITY matching rules for the attribute type or
subtype. The filter is TRUE when either the ORDERING or EQUALITY
rule returns TRUE as applied to the attribute or subtype and the
asserted value.
4.5.1.7.5. SearchRequest.filter.present
A present filter is TRUE when there is an attribute or subtype of the
specified attribute description present in an entry, FALSE when no
attribute or subtype of the specified attribute description is
present in an entry, and Undefined otherwise.
4.5.1.7.6. SearchRequest.filter.approxMatch
An approxMatch filter is TRUE when there is a value of the attribute
type or subtype for which some locally-defined approximate matching
algorithm (e.g., spelling variations, phonetic match, etc.) returns
TRUE. If a value matches for equality, it also satisfies an
approximate match. If approximate matching is not supported for the
attribute, this filter item should be treated as an equalityMatch.
4.5.1.7.7. SearchRequest.filter.extensibleMatch
The fields of the extensibleMatch filter item are evaluated as
follows:
- If the matchingRule field is absent, the type field MUST be
present, and an equality match is performed for that type.
- If the type field is absent and the matchingRule is present, the
matchValue is compared against all attributes in an entry that
support that matchingRule.
- If the type field is present and the matchingRule is present, the
matchValue is compared against the specified attribute type and its
subtypes.
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- If the dnAttributes field is set to TRUE, the match is additionally
applied against all the AttributeValueAssertions in an entry's
distinguished name, and it evaluates to TRUE if there is at least
one attribute or subtype in the distinguished name for which the
filter item evaluates to TRUE. The dnAttributes field is present
to alleviate the need for multiple versions of generic matching
rules (such as word matching), where one applies to entries and
another applies to entries and DN attributes as well.
The matchingRule used for evaluation determines the syntax for the
assertion value. Once the matchingRule and attribute(s) have been
determined, the filter item evaluates to TRUE if it matches at least
one attribute type or subtype in the entry, FALSE if it does not
match any attribute type or subtype in the entry, and Undefined if
the matchingRule is not recognized, the matchingRule is unsuitable
for use with the specified type, or the assertionValue is invalid.
4.5.1.8. SearchRequest.attributes
A selection list of the attributes to be returned from each entry
that matches the search filter. Attributes that are subtypes of
listed attributes are implicitly included. LDAPString values of this
field are constrained to the following Augmented Backus-Naur Form
(ABNF) [RFC4234]:
attributeSelector = attributedescription / selectorspecial
selectorspecial = noattrs / alluserattrs
noattrs = %x31.2E.31 ; "1.1"
alluserattrs = %x2A ; asterisk ("*")
The <attributedescription> production is defined in Section 2.5 of
[RFC4512].
There are three special cases that may appear in the attributes
selection list:
1. An empty list with no attributes requests the return of all
user attributes.
2. A list containing "*" (with zero or more attribute
descriptions) requests the return of all user attributes in
addition to other listed (operational) attributes.
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3. A list containing only the OID "1.1" indicates that no
attributes are to be returned. If "1.1" is provided with other
attributeSelector values, the "1.1" attributeSelector is
ignored. This OID was chosen because it does not (and can not)
correspond to any attribute in use.
Client implementors should note that even if all user attributes are
requested, some attributes and/or attribute values of the entry may
not be included in Search results due to access controls or other
restrictions. Furthermore, servers will not return operational
attributes, such as objectClasses or attributeTypes, unless they are
listed by name. Operational attributes are described in [RFC4512].
Attributes are returned at most once in an entry. If an attribute
description is named more than once in the list, the subsequent names
are ignored. If an attribute description in the list is not
recognized, it is ignored by the server.
4.5.2. Search Result
The results of the Search operation are returned as zero or more
SearchResultEntry and/or SearchResultReference messages, followed by
a single SearchResultDone message.
SearchResultEntry ::= [APPLICATION 4] SEQUENCE {
objectName LDAPDN,
attributes PartialAttributeList }
PartialAttributeList ::= SEQUENCE OF
partialAttribute PartialAttribute
SearchResultReference ::= [APPLICATION 19] SEQUENCE
SIZE (1..MAX) OF uri URI
SearchResultDone ::= [APPLICATION 5] LDAPResult
Each SearchResultEntry represents an entry found during the Search.
Each SearchResultReference represents an area not yet explored during
the Search. The SearchResultEntry and SearchResultReference messages
may come in any order. Following all the SearchResultReference and
SearchResultEntry responses, the server returns a SearchResultDone
response, which contains an indication of success or details any
errors that have occurred.
Each entry returned in a SearchResultEntry will contain all
appropriate attributes as specified in the attributes field of the
Search Request, subject to access control and other administrative
policy. Note that the PartialAttributeList may hold zero elements.
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This may happen when none of the attributes of an entry were
requested or could be returned. Note also that the partialAttribute
vals set may hold zero elements. This may happen when typesOnly is
requested, access controls prevent the return of values, or other
reasons.
Some attributes may be constructed by the server and appear in a
SearchResultEntry attribute list, although they are not stored
attributes of an entry. Clients SHOULD NOT assume that all
attributes can be modified, even if this is permitted by access
control.
If the server's schema defines short names [RFC4512] for an attribute
type, then the server SHOULD use one of those names in attribute
descriptions for that attribute type (in preference to using the
<numericoid> [RFC4512] format of the attribute type's object
identifier). The server SHOULD NOT use the short name if that name
is known by the server to be ambiguous, or if it is otherwise likely
to cause interoperability problems.
4.5.3. Continuation References in the Search Result
If the server was able to locate the entry referred to by the
baseObject but was unable or unwilling to search one or more non-
local entries, the server may return one or more
SearchResultReference messages, each containing a reference to
another set of servers for continuing the operation. A server MUST
NOT return any SearchResultReference messages if it has not located
the baseObject and thus has not searched any entries. In this case,
it would return a SearchResultDone containing either a referral or
noSuchObject result code (depending on the server's knowledge of the
entry named in the baseObject).
If a server holds a copy or partial copy of the subordinate naming
context (Section 5 of [RFC4512]), it may use the search filter to
determine whether or not to return a SearchResultReference response.
Otherwise, SearchResultReference responses are always returned when
in scope.
The SearchResultReference is of the same data type as the Referral.
If the client wishes to progress the Search, it issues a new Search
operation for each SearchResultReference that is returned. If
multiple URIs are present, the client assumes that any supported URI
may be used to progress the operation.
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Clients that follow search continuation references MUST ensure that
they do not loop between servers. They MUST NOT repeatedly contact
the same server for the same request with the same parameters. Some
clients use a counter that is incremented each time search result
reference handling occurs for an operation, and these kinds of
clients MUST be able to handle at least ten nested referrals while
progressing the operation.
Note that the Abandon operation described in Section 4.11 applies
only to a particular operation sent at the LDAP message layer between
a client and server. The client must individually abandon subsequent
Search operations it wishes to.
A URI for a server implementing LDAP and accessible via TCP/IP (v4 or
v6) [RFC793][RFC791] is written as an LDAP URL according to
[RFC4516].
SearchResultReference values that are LDAP URLs follow these rules:
- The <dn> part of the LDAP URL MUST be present, with the new target
object name. The client uses this name when following the
reference.
- Some servers (e.g., participating in distributed indexing) may
provide a different filter in the LDAP URL.
- If the <filter> part of the LDAP URL is present, the client uses
this filter in its next request to progress this Search, and if it
is not present the client uses the same filter as it used for that
Search.
- If the originating search scope was singleLevel, the <scope> part
of the LDAP URL will be "base".
- It is RECOMMENDED that the <scope> part be present to avoid
ambiguity. In the absence of a <scope> part, the scope of the
original Search request is assumed.
- Other aspects of the new Search request may be the same as or
different from the Search request that generated the
SearchResultReference.
- The name of an unexplored subtree in a SearchResultReference need
not be subordinate to the base object.
Other kinds of URIs may be returned. The syntax and semantics of
such URIs is left to future specifications. Clients may ignore URIs
that they do not support.
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UTF-8-encoded characters appearing in the string representation of a
DN, search filter, or other fields of the referral value may not be
legal for URIs (e.g., spaces) and MUST be escaped using the % method
in [RFC3986].
4.5.3.1. Examples
For example, suppose the contacted server (hosta) holds the entry
<DC=Example,DC=NET> and the entry <CN=Manager,DC=Example,DC=NET>. It
knows that both LDAP servers (hostb) and (hostc) hold
<OU=People,DC=Example,DC=NET> (one is the master and the other server
a shadow), and that LDAP-capable server (hostd) holds the subtree
<OU=Roles,DC=Example,DC=NET>. If a wholeSubtree Search of
<DC=Example,DC=NET> is requested to the contacted server, it may
return the following:
SearchResultEntry for DC=Example,DC=NET
SearchResultEntry for CN=Manager,DC=Example,DC=NET
SearchResultReference {
ldap://hostb/OU=People,DC=Example,DC=NET??sub
ldap://hostc/OU=People,DC=Example,DC=NET??sub }
SearchResultReference {
ldap://hostd/OU=Roles,DC=Example,DC=NET??sub }
SearchResultDone (success)
Client implementors should note that when following a
SearchResultReference, additional SearchResultReference may be
generated. Continuing the example, if the client contacted the
server (hostb) and issued the Search request for the subtree
<OU=People,DC=Example,DC=NET>, the server might respond as follows:
SearchResultEntry for OU=People,DC=Example,DC=NET
SearchResultReference {
ldap://hoste/OU=Managers,OU=People,DC=Example,DC=NET??sub }
SearchResultReference {
ldap://hostf/OU=Consultants,OU=People,DC=Example,DC=NET??sub }
SearchResultDone (success)
Similarly, if a singleLevel Search of <DC=Example,DC=NET> is
requested to the contacted server, it may return the following:
SearchResultEntry for CN=Manager,DC=Example,DC=NET
SearchResultReference {
ldap://hostb/OU=People,DC=Example,DC=NET??base
ldap://hostc/OU=People,DC=Example,DC=NET??base }
SearchResultReference {
ldap://hostd/OU=Roles,DC=Example,DC=NET??base }
SearchResultDone (success)
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If the contacted server does not hold the base object for the Search,
but has knowledge of its possible location, then it may return a
referral to the client. In this case, if the client requests a
subtree Search of <DC=Example,DC=ORG> to hosta, the server returns a
SearchResultDone containing a referral.
SearchResultDone (referral) {
ldap://hostg/DC=Example,DC=ORG??sub }
4.6. Modify Operation
The Modify operation allows a client to request that a modification
of an entry be performed on its behalf by a server. The Modify
Request is defined as follows:
ModifyRequest ::= [APPLICATION 6] SEQUENCE {
object LDAPDN,
changes SEQUENCE OF change SEQUENCE {
operation ENUMERATED {
add (0),
delete (1),
replace (2),
... },
modification PartialAttribute } }
Fields of the Modify Request are:
- object: The value of this field contains the name of the entry to
be modified. The server SHALL NOT perform any alias dereferencing
in determining the object to be modified.
- changes: A list of modifications to be performed on the entry. The
entire list of modifications MUST be performed in the order they
are listed as a single atomic operation. While individual
modifications may violate certain aspects of the directory schema
(such as the object class definition and Directory Information Tree
(DIT) content rule), the resulting entry after the entire list of
modifications is performed MUST conform to the requirements of the
directory model and controlling schema [RFC4512].
- operation: Used to specify the type of modification being
performed. Each operation type acts on the following
modification. The values of this field have the following
semantics, respectively:
add: add values listed to the modification attribute,
creating the attribute if necessary.
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delete: delete values listed from the modification attribute.
If no values are listed, or if all current values of the
attribute are listed, the entire attribute is removed.
replace: replace all existing values of the modification
attribute with the new values listed, creating the attribute
if it did not already exist. A replace with no value will
delete the entire attribute if it exists, and it is ignored
if the attribute does not exist.
- modification: A PartialAttribute (which may have an empty SET
of vals) used to hold the attribute type or attribute type and
values being modified.
Upon receipt of a Modify Request, the server attempts to perform the
necessary modifications to the DIT and returns the result in a Modify
Response, defined as follows:
ModifyResponse ::= [APPLICATION 7] LDAPResult
The server will return to the client a single Modify Response
indicating either the successful completion of the DIT modification,
or the reason that the modification failed. Due to the requirement
for atomicity in applying the list of modifications in the Modify
Request, the client may expect that no modifications of the DIT have
been performed if the Modify Response received indicates any sort of
error, and that all requested modifications have been performed if
the Modify Response indicates successful completion of the Modify
operation. Whether or not the modification was applied cannot be
determined by the client if the Modify Response was not received
(e.g., the LDAP session was terminated or the Modify operation was
abandoned).
Servers MUST ensure that entries conform to user and system schema
rules or other data model constraints. The Modify operation cannot
be used to remove from an entry any of its distinguished values,
i.e., those values which form the entry's relative distinguished
name. An attempt to do so will result in the server returning the
notAllowedOnRDN result code. The Modify DN operation described in
Section 4.9 is used to rename an entry.
For attribute types that specify no equality matching, the rules in
Section 2.5.1 of [RFC4512] are followed.
Note that due to the simplifications made in LDAP, there is not a
direct mapping of the changes in an LDAP ModifyRequest onto the
changes of a DAP ModifyEntry operation, and different implementations
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of LDAP-DAP gateways may use different means of representing the
change. If successful, the final effect of the operations on the
entry MUST be identical.
4.7. Add Operation
The Add operation allows a client to request the addition of an entry
into the Directory. The Add Request is defined as follows:
AddRequest ::= [APPLICATION 8] SEQUENCE {
entry LDAPDN,
attributes AttributeList }
AttributeList ::= SEQUENCE OF attribute Attribute
Fields of the Add Request are:
- entry: the name of the entry to be added. The server SHALL NOT
dereference any aliases in locating the entry to be added.
- attributes: the list of attributes that, along with those from the
RDN, make up the content of the entry being added. Clients MAY or
MAY NOT include the RDN attribute(s) in this list. Clients MUST
NOT supply NO-USER-MODIFICATION attributes such as the
createTimestamp or creatorsName attributes, since the server
maintains these automatically.
Servers MUST ensure that entries conform to user and system schema
rules or other data model constraints. For attribute types that
specify no equality matching, the rules in Section 2.5.1 of [RFC4512]
are followed (this applies to the naming attribute in addition to any
multi-valued attributes being added).
The entry named in the entry field of the AddRequest MUST NOT exist
for the AddRequest to succeed. The immediate superior (parent) of an
object or alias entry to be added MUST exist. For example, if the
client attempted to add <CN=JS,DC=Example,DC=NET>, the
<DC=Example,DC=NET> entry did not exist, and the <DC=NET> entry did
exist, then the server would return the noSuchObject result code with
the matchedDN field containing <DC=NET>.
Upon receipt of an Add Request, a server will attempt to add the
requested entry. The result of the Add attempt will be returned to
the client in the Add Response, defined as follows:
AddResponse ::= [APPLICATION 9] LDAPResult
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A response of success indicates that the new entry has been added to
the Directory.
4.8. Delete Operation
The Delete operation allows a client to request the removal of an
entry from the Directory. The Delete Request is defined as follows:
DelRequest ::= [APPLICATION 10] LDAPDN
The Delete Request consists of the name of the entry to be deleted.
The server SHALL NOT dereference aliases while resolving the name of
the target entry to be removed.
Only leaf entries (those with no subordinate entries) can be deleted
with this operation.
Upon receipt of a Delete Request, a server will attempt to perform
the entry removal requested and return the result in the Delete
Response defined as follows:
DelResponse ::= [APPLICATION 11] LDAPResult
4.9. Modify DN Operation
The Modify DN operation allows a client to change the Relative
Distinguished Name (RDN) of an entry in the Directory and/or to move
a subtree of entries to a new location in the Directory. The Modify
DN Request is defined as follows:
ModifyDNRequest ::= [APPLICATION 12] SEQUENCE {
entry LDAPDN,
newrdn RelativeLDAPDN,
deleteoldrdn BOOLEAN,
newSuperior [0] LDAPDN OPTIONAL }
Fields of the Modify DN Request are:
- entry: the name of the entry to be changed. This entry may or may
not have subordinate entries.
- newrdn: the new RDN of the entry. The value of the old RDN is
supplied when moving the entry to a new superior without changing
its RDN. Attribute values of the new RDN not matching any
attribute value of the entry are added to the entry, and an
appropriate error is returned if this fails.
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- deleteoldrdn: a boolean field that controls whether the old RDN
attribute values are to be retained as attributes of the entry or
deleted from the entry.
- newSuperior: if present, this is the name of an existing object
entry that becomes the immediate superior (parent) of the
existing entry.
The server SHALL NOT dereference any aliases in locating the objects
named in entry or newSuperior.
Upon receipt of a ModifyDNRequest, a server will attempt to perform
the name change and return the result in the Modify DN Response,
defined as follows:
ModifyDNResponse ::= [APPLICATION 13] LDAPResult
For example, if the entry named in the entry field was <cn=John
Smith,c=US>, the newrdn field was <cn=John Cougar Smith>, and the
newSuperior field was absent, then this operation would attempt to
rename the entry as <cn=John Cougar Smith,c=US>. If there was
already an entry with that name, the operation would fail with the
entryAlreadyExists result code.
Servers MUST ensure that entries conform to user and system schema
rules or other data model constraints. For attribute types that
specify no equality matching, the rules in Section 2.5.1 of [RFC4512]
are followed (this pertains to newrdn and deleteoldrdn).
The object named in newSuperior MUST exist. For example, if the
client attempted to add <CN=JS,DC=Example,DC=NET>, the
<DC=Example,DC=NET> entry did not exist, and the <DC=NET> entry did
exist, then the server would return the noSuchObject result code with
the matchedDN field containing <DC=NET>.
If the deleteoldrdn field is TRUE, the attribute values forming the
old RDN (but not the new RDN) are deleted from the entry. If the
deleteoldrdn field is FALSE, the attribute values forming the old RDN
will be retained as non-distinguished attribute values of the entry.
Note that X.500 restricts the ModifyDN operation to affect only
entries that are contained within a single server. If the LDAP
server is mapped onto DAP, then this restriction will apply, and the
affectsMultipleDSAs result code will be returned if this error
occurred. In general, clients MUST NOT expect to be able to perform
arbitrary movements of entries and subtrees between servers or
between naming contexts.
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4.10. Compare Operation
The Compare operation allows a client to compare an assertion value
with the values of a particular attribute in a particular entry in
the Directory. The Compare Request is defined as follows:
CompareRequest ::= [APPLICATION 14] SEQUENCE {
entry LDAPDN,
ava AttributeValueAssertion }
Fields of the Compare Request are:
- entry: the name of the entry to be compared. The server SHALL NOT
dereference any aliases in locating the entry to be compared.
- ava: holds the attribute value assertion to be compared.
Upon receipt of a Compare Request, a server will attempt to perform
the requested comparison and return the result in the Compare
Response, defined as follows:
CompareResponse ::= [APPLICATION 15] LDAPResult
The resultCode is set to compareTrue, compareFalse, or an appropriate
error. compareTrue indicates that the assertion value in the ava
field matches a value of the attribute or subtype according to the
attribute's EQUALITY matching rule. compareFalse indicates that the
assertion value in the ava field and the values of the attribute or
subtype did not match. Other result codes indicate either that the
result of the comparison was Undefined (Section 4.5.1.7), or that
some error occurred.
Note that some directory systems may establish access controls that
permit the values of certain attributes (such as userPassword) to be
compared but not interrogated by other means.
4.11. Abandon Operation
The function of the Abandon operation is to allow a client to request
that the server abandon an uncompleted operation. The Abandon
Request is defined as follows:
AbandonRequest ::= [APPLICATION 16] MessageID
The MessageID is that of an operation that was requested earlier at
this LDAP message layer. The Abandon request itself has its own
MessageID. This is distinct from the MessageID of the earlier
operation being abandoned.
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There is no response defined in the Abandon operation. Upon receipt
of an AbandonRequest, the server MAY abandon the operation identified
by the MessageID. Since the client cannot tell the difference
between a successfully abandoned operation and an uncompleted
operation, the application of the Abandon operation is limited to
uses where the client does not require an indication of its outcome.
Abandon, Bind, Unbind, and StartTLS operations cannot be abandoned.
In the event that a server receives an Abandon Request on a Search
operation in the midst of transmitting responses to the Search, that
server MUST cease transmitting entry responses to the abandoned
request immediately, and it MUST NOT send the SearchResultDone. Of
course, the server MUST ensure that only properly encoded LDAPMessage
PDUs are transmitted.
The ability to abandon other (particularly update) operations is at
the discretion of the server.
Clients should not send Abandon requests for the same operation
multiple times, and they MUST also be prepared to receive results
from operations they have abandoned (since these might have been in
transit when the Abandon was requested or might not be able to be
abandoned).
Servers MUST discard Abandon requests for messageIDs they do not
recognize, for operations that cannot be abandoned, and for
operations that have already been abandoned.
4.12. Extended Operation
The Extended operation allows additional operations to be defined for
services not already available in the protocol; for example, to Add
operations to install transport layer security (see Section 4.14).
The Extended operation allows clients to make requests and receive
responses with predefined syntaxes and semantics. These may be
defined in RFCs or be private to particular implementations.
Each Extended operation consists of an Extended request and an
Extended response.
ExtendedRequest ::= [APPLICATION 23] SEQUENCE {
requestName [0] LDAPOID,
requestValue [1] OCTET STRING OPTIONAL }
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The requestName is a dotted-decimal representation of the unique
OBJECT IDENTIFIER corresponding to the request. The requestValue is
information in a form defined by that request, encapsulated inside an
OCTET STRING.
The server will respond to this with an LDAPMessage containing an
ExtendedResponse.
ExtendedResponse ::= [APPLICATION 24] SEQUENCE {
COMPONENTS OF LDAPResult,
responseName [10] LDAPOID OPTIONAL,
responseValue [11] OCTET STRING OPTIONAL }
The responseName field, when present, contains an LDAPOID that is
unique for this extended operation or response. This field is
optional (even when the extension specification defines an LDAPOID
for use in this field). The field will be absent whenever the server
is unable or unwilling to determine the appropriate LDAPOID to
return, for instance, when the requestName cannot be parsed or its
value is not recognized.
Where the requestName is not recognized, the server returns
protocolError. (The server may return protocolError in other cases.)
The requestValue and responseValue fields contain information
associated with the operation. The format of these fields is defined
by the specification of the Extended operation. Implementations MUST
be prepared to handle arbitrary contents of these fields, including
zero bytes. Values that are defined in terms of ASN.1 and BER-
encoded according to Section 5.1 also follow the extensibility rules
in Section 4.
Servers list the requestName of Extended Requests they recognize in
the 'supportedExtension' attribute in the root DSE (Section 5.1 of
[RFC4512]).
Extended operations may be specified in other documents. The
specification of an Extended operation consists of:
- the OBJECT IDENTIFIER assigned to the requestName,
- the OBJECT IDENTIFIER (if any) assigned to the responseName (note
that the same OBJECT IDENTIFIER may be used for both the
requestName and responseName),
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- the format of the contents of the requestValue and responseValue
(if any), and
- the semantics of the operation.
4.13. IntermediateResponse Message
While the Search operation provides a mechanism to return multiple
response messages for a single Search request, other operations, by
nature, do not provide for multiple response messages.
The IntermediateResponse message provides a general mechanism for
defining single-request/multiple-response operations in LDAP. This
message is intended to be used in conjunction with the Extended
operation to define new single-request/multiple-response operations
or in conjunction with a control when extending existing LDAP
operations in a way that requires them to return Intermediate
response information.
It is intended that the definitions and descriptions of Extended
operations and controls that make use of the IntermediateResponse
message will define the circumstances when an IntermediateResponse
message can be sent by a server and the associated meaning of an
IntermediateResponse message sent in a particular circumstance.
IntermediateResponse ::= [APPLICATION 25] SEQUENCE {
responseName [0] LDAPOID OPTIONAL,
responseValue [1] OCTET STRING OPTIONAL }
IntermediateResponse messages SHALL NOT be returned to the client
unless the client issues a request that specifically solicits their
return. This document defines two forms of solicitation: Extended
operation and request control. IntermediateResponse messages are
specified in documents describing the manner in which they are
solicited (i.e., in the Extended operation or request control
specification that uses them). These specifications include:
- the OBJECT IDENTIFIER (if any) assigned to the responseName,
- the format of the contents of the responseValue (if any), and
- the semantics associated with the IntermediateResponse message.
Extensions that allow the return of multiple types of
IntermediateResponse messages SHALL identify those types using unique
responseName values (note that one of these may specify no value).
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Sections 4.13.1 and 4.13.2 describe additional requirements on the
inclusion of responseName and responseValue in IntermediateResponse
messages.
4.13.1. Usage with LDAP ExtendedRequest and ExtendedResponse
A single-request/multiple-response operation may be defined using a
single ExtendedRequest message to solicit zero or more
IntermediateResponse messages of one or more kinds, followed by an
ExtendedResponse message.
4.13.2. Usage with LDAP Request Controls
A control's semantics may include the return of zero or more
IntermediateResponse messages prior to returning the final result
code for the operation. One or more kinds of IntermediateResponse
messages may be sent in response to a request control.
All IntermediateResponse messages associated with request controls
SHALL include a responseName. This requirement ensures that the
client can correctly identify the source of IntermediateResponse
messages when:
- two or more controls using IntermediateResponse messages are
included in a request for any LDAP operation or
- one or more controls using IntermediateResponse messages are
included in a request with an LDAP Extended operation that uses
IntermediateResponse messages.
4.14. StartTLS Operation
The Start Transport Layer Security (StartTLS) operation's purpose is
to initiate installation of a TLS layer. The StartTLS operation is
defined using the Extended operation mechanism described in Section
4.12.
4.14.1. StartTLS Request
A client requests TLS establishment by transmitting a StartTLS
request message to the server. The StartTLS request is defined in
terms of an ExtendedRequest. The requestName is
"1.3.6.1.4.1.1466.20037", and the requestValue field is always
absent.
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The client MUST NOT send any LDAP PDUs at this LDAP message layer
following this request until it receives a StartTLS Extended response
and, in the case of a successful response, completes TLS
negotiations.
Detected sequencing problems (particularly those detailed in Section
3.1.1 of [RFC4513]) result in the resultCode being set to
operationsError.
If the server does not support TLS (whether by design or by current
configuration), it returns with the resultCode set to protocolError
as described in Section 4.12.
4.14.2. StartTLS Response
When a StartTLS request is received, servers supporting the operation
MUST return a StartTLS response message to the requestor. The
responseName is "1.3.6.1.4.1.1466.20037" when provided (see Section
4.12). The responseValue is always absent.
If the server is willing and able to negotiate TLS, it returns the
StartTLS response with the resultCode set to success. Upon client
receipt of a successful StartTLS response, protocol peers may
commence with TLS negotiation as discussed in Section 3 of [RFC4513].
If the server is otherwise unwilling or unable to perform this
operation, the server is to return an appropriate result code
indicating the nature of the problem. For example, if the TLS
subsystem is not presently available, the server may indicate this by
returning with the resultCode set to unavailable. In cases where a
non-success result code is returned, the LDAP session is left without
a TLS layer.
4.14.3. Removal of the TLS Layer
Either the client or server MAY remove the TLS layer and leave the
LDAP message layer intact by sending and receiving a TLS closure
alert.
The initiating protocol peer sends the TLS closure alert and MUST
wait until it receives a TLS closure alert from the other peer before
sending further LDAP PDUs.
When a protocol peer receives the initial TLS closure alert, it may
choose to allow the LDAP message layer to remain intact. In this
case, it MUST immediately transmit a TLS closure alert. Following
this, it MAY send and receive LDAP PDUs.
Sermersheim Standards Track [Page 41]
RFC 4511 LDAPv3 June 2006
Protocol peers MAY terminate the LDAP session after sending or
receiving a TLS closure alert.
5. Protocol Encoding, Connection, and Transfer
This protocol is designed to run over connection-oriented, reliable
transports, where the data stream is divided into octets (8-bit
units), with each octet and each bit being significant.
One underlying service, LDAP over TCP, is defined in Section 5.2.
This service is generally applicable to applications providing or
consuming X.500-based directory services on the Internet. This
specification was generally written with the TCP mapping in mind.
Specifications detailing other mappings may encounter various
obstacles.
Implementations of LDAP over TCP MUST implement the mapping as
described in Section 5.2.
This table illustrates the relationship among the different layers
involved in an exchange between two protocol peers:
+----------------------+
| LDAP message layer |
+----------------------+ > LDAP PDUs
+----------------------+ < data
| SASL layer |
+----------------------+ > SASL-protected data
+----------------------+ < data
| TLS layer |
Application +----------------------+ > TLS-protected data
------------+----------------------+ < data
Transport | transport connection |
+----------------------+
5.1. Protocol Encoding
The protocol elements of LDAP SHALL be encoded for exchange using the
Basic Encoding Rules [BER] of [ASN.1] with the following
restrictions:
- Only the definite form of length encoding is used.
- OCTET STRING values are encoded in the primitive form only.
- If the value of a BOOLEAN type is true, the encoding of the value
octet is set to hex "FF".
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RFC 4511 LDAPv3 June 2006
- If a value of a type is its default value, it is absent. Only some
BOOLEAN and INTEGER types have default values in this protocol
definition.
These restrictions are meant to ease the overhead of encoding and
decoding certain elements in BER.
These restrictions do not apply to ASN.1 types encapsulated inside of
OCTET STRING values, such as attribute values, unless otherwise
stated.
5.2. Transmission Control Protocol (TCP)
The encoded LDAPMessage PDUs are mapped directly onto the TCP
[RFC793] bytestream using the BER-based encoding described in Section
5.1. It is recommended that server implementations running over the
TCP provide a protocol listener on the Internet Assigned Numbers
Authority (IANA)-assigned LDAP port, 389 [PortReg]. Servers may
instead provide a listener on a different port number. Clients MUST
support contacting servers on any valid TCP port.
5.3. Termination of the LDAP session
Termination of the LDAP session is typically initiated by the client
sending an UnbindRequest (Section 4.3), or by the server sending a
Notice of Disconnection (Section 4.4.1). In these cases, each
protocol peer gracefully terminates the LDAP session by ceasing
exchanges at the LDAP message layer, tearing down any SASL layer,
tearing down any TLS layer, and closing the transport connection.
A protocol peer may determine that the continuation of any
communication would be pernicious, and in this case, it may abruptly
terminate the session by ceasing communication and closing the
transport connection.
In either case, when the LDAP session is terminated, uncompleted
operations are handled as specified in Section 3.1.
6. Security Considerations
This version of the protocol provides facilities for simple
authentication using a cleartext password, as well as any SASL
[RFC4422] mechanism. Installing SASL and/or TLS layers can provide
integrity and other data security services.
It is also permitted that the server can return its credentials to
the client, if it chooses to do so.
Sermersheim Standards Track [Page 43]
RFC 4511 LDAPv3 June 2006
Use of cleartext password is strongly discouraged where the
underlying transport service cannot guarantee confidentiality and may
result in disclosure of the password to unauthorized parties.
Servers are encouraged to prevent directory modifications by clients
that have authenticated anonymously [RFC4513].
Security considerations for authentication methods, SASL mechanisms,
and TLS are described in [RFC4513].
Note that SASL authentication exchanges do not provide data
confidentiality or integrity protection for the version or name
fields of the BindRequest or the resultCode, diagnosticMessage, or
referral fields of the BindResponse, nor for any information
contained in controls attached to Bind requests or responses. Thus,
information contained in these fields SHOULD NOT be relied on unless
it is otherwise protected (such as by establishing protections at the
transport layer).
Implementors should note that various security factors (including
authentication and authorization information and data security
services) may change during the course of the LDAP session or even
during the performance of a particular operation. For instance,
credentials could expire, authorization identities or access controls
could change, or the underlying security layer(s) could be replaced
or terminated. Implementations should be robust in the handling of
changing security factors.
In some cases, it may be appropriate to continue the operation even
in light of security factor changes. For instance, it may be
appropriate to continue an Abandon operation regardless of the
change, or to continue an operation when the change upgraded (or
maintained) the security factor. In other cases, it may be
appropriate to fail or alter the processing of the operation. For
instance, if confidential protections were removed, it would be
appropriate either to fail a request to return sensitive data or,
minimally, to exclude the return of sensitive data.
Implementations that cache attributes and entries obtained via LDAP
MUST ensure that access controls are maintained if that information
is to be provided to multiple clients, since servers may have access
control policies that prevent the return of entries or attributes in
Search results except to particular authenticated clients. For
example, caches could serve result information only to the client
whose request caused it to be in the cache.
Sermersheim Standards Track [Page 44]
RFC 4511 LDAPv3 June 2006
Servers may return referrals or Search result references that
redirect clients to peer servers. It is possible for a rogue
application to inject such referrals into the data stream in an
attempt to redirect a client to a rogue server. Clients are advised
to be aware of this and possibly reject referrals when
confidentiality measures are not in place. Clients are advised to
reject referrals from the StartTLS operation.
The matchedDN and diagnosticMessage fields, as well as some
resultCode values (e.g., attributeOrValueExists and
entryAlreadyExists), could disclose the presence or absence of
specific data in the directory that is subject to access and other
administrative controls. Server implementations should restrict
access to protected information equally under both normal and error
conditions.
Protocol peers MUST be prepared to handle invalid and arbitrary-
length protocol encodings. Invalid protocol encodings include: BER
encoding exceptions, format string and UTF-8 encoding exceptions,
overflow exceptions, integer value exceptions, and binary mode on/off
flag exceptions. The LDAPv3 PROTOS [PROTOS-LDAP] test suite provides
excellent examples of these exceptions and test cases used to
discover flaws.
In the event that a protocol peer senses an attack that in its nature
could cause damage due to further communication at any layer in the
LDAP session, the protocol peer should abruptly terminate the LDAP
session as described in Section 5.3.
7. Acknowledgements
This document is based on RFC 2251 by Mark Wahl, Tim Howes, and Steve
Kille. RFC 2251 was a product of the IETF ASID Working Group.
It is also based on RFC 2830 by Jeff Hodges, RL "Bob" Morgan, and
Mark Wahl. RFC 2830 was a product of the IETF LDAPEXT Working Group.
It is also based on RFC 3771 by Roger Harrison and Kurt Zeilenga.
RFC 3771 was an individual submission to the IETF.
This document is a product of the IETF LDAPBIS Working Group.
Significant contributors of technical review and content include Kurt
Zeilenga, Steven Legg, and Hallvard Furuseth.
Sermersheim Standards Track [Page 45]
RFC 4511 LDAPv3 June 2006
8. Normative References
[ASN.1] ITU-T Recommendation X.680 (07/2002) | ISO/IEC 8824-
1:2002 "Information Technology - Abstract Syntax
Notation One (ASN.1): Specification of basic notation".
[BER] ITU-T Rec. X.690 (07/2002) | ISO/IEC 8825-1:2002,
"Information technology - ASN.1 encoding rules:
Specification of Basic Encoding Rules (BER), Canonical
Encoding Rules (CER) and Distinguished Encoding Rules
(DER)", 2002.
[ISO10646] Universal Multiple-Octet Coded Character Set (UCS) -
Architecture and Basic Multilingual Plane, ISO/IEC
10646-1 : 1993.
[RFC791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, September 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3454] Hoffman P. and M. Blanchet, "Preparation of
Internationalized Strings ('stringprep')", RFC 3454,
December 2002.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter,
"Uniform Resource Identifier (URI): Generic Syntax",
STD 66, RFC 3986, January 2005.
[RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User
Names and Passwords", RFC 4013, February 2005.
[RFC4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.
[RFC4346] Dierks, T. and E. Rescorla, "The TLS Protocol Version
1.1", RFC 4346, March 2006.
[RFC4422] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple
Authentication and Security Layer (SASL)", RFC 4422,
June 2006.
Sermersheim Standards Track [Page 46]
RFC 4511 LDAPv3 June 2006
[RFC4510] Zeilenga, K., Ed., "Lightweight Directory Access
Protocol (LDAP): Technical Specification Road Map", RFC
4510, June 2006.
[RFC4512] Zeilenga, K., Lightweight Directory Access Protocol
(LDAP): Directory Information Models", RFC 4512, June
2006.
[RFC4513] Harrison, R., Ed., "Lightweight Directory Access
Protocol (LDAP): Authentication Methods and Security
Mechanisms", RFC 4513, June 2006.
[RFC4514] Zeilenga, K., Ed., "Lightweight Directory Access
Protocol (LDAP): String Representation of Distinguished
Names", RFC 4514, June 2006.
[RFC4516] Smith, M., Ed. and T. Howes, "Lightweight Directory
Access Protocol (LDAP): Uniform Resource Locator", RFC
4516, June 2006.
[RFC4517] Legg, S., Ed., "Lightweight Directory Access Protocol
(LDAP): Syntaxes and Matching Rules", RFC 4517, June
2006.
[RFC4520] Zeilenga, K., "Internet Assigned Numbers Authority
(IANA) Considerations for the Lightweight Directory
Access Protocol (LDAP)", BCP 64, RFC 4520, June 2006.
[Unicode] The Unicode Consortium, "The Unicode Standard, Version
3.2.0" is defined by "The Unicode Standard, Version
3.0" (Reading, MA, Addison-Wesley, 2000. ISBN 0-201-
61633-5), as amended by the "Unicode Standard Annex
#27: Unicode 3.1"
(http://www.unicode.org/reports/tr27/) and by the
"Unicode Standard Annex #28: Unicode 3.2"
(http://www.unicode.org/reports/tr28/).
[X.500] ITU-T Rec. X.500, "The Directory: Overview of Concepts,
Models and Service", 1993.
[X.511] ITU-T Rec. X.511, "The Directory: Abstract Service
Definition", 1993.
Sermersheim Standards Track [Page 47]
RFC 4511 LDAPv3 June 2006
9. Informative References
[CharModel] Whistler, K. and M. Davis, "Unicode Technical Report
#17, Character Encoding Model", UTR17,
<http://www.unicode.org/unicode/reports/tr17/>, August
2000.
[Glossary] The Unicode Consortium, "Unicode Glossary",
<http://www.unicode.org/glossary/>.
[PortReg] IANA, "Port Numbers",
<http://www.iana.org/assignments/port-numbers>.
[PROTOS-LDAP] University of Oulu, "PROTOS Test-Suite: c06-ldapv3"
<http://www.ee.oulu.fi/research/ouspg/protos/testing/
c06/ldapv3/>.
10. IANA Considerations
The Internet Assigned Numbers Authority (IANA) has updated the LDAP
result code registry to indicate that this document provides the
definitive technical specification for result codes 0-36, 48-54, 64-
70, 80-90. It is also noted that one resultCode value
(strongAuthRequired) has been renamed (to strongerAuthRequired).
The IANA has also updated the LDAP Protocol Mechanism registry to
indicate that this document and [RFC4513] provides the definitive
technical specification for the StartTLS (1.3.6.1.4.1.1466.20037)
Extended operation.
IANA has assigned LDAP Object Identifier 18 [RFC4520] to identify the
ASN.1 module defined in this document.
Subject: Request for LDAP Object Identifier Registration
Person & email address to contact for further information:
Jim Sermersheim <jimse@novell.com>
Specification: RFC 4511
Author/Change Controller: IESG
Comments:
Identifies the LDAP ASN.1 module
Sermersheim Standards Track [Page 48]
RFC 4511 LDAPv3 June 2006
Appendix A. LDAP Result Codes
This normative appendix details additional considerations regarding
LDAP result codes and provides a brief, general description of each
LDAP result code enumerated in Section 4.1.9.
Additional result codes MAY be defined for use with extensions
[RFC4520]. Client implementations SHALL treat any result code that
they do not recognize as an unknown error condition.
The descriptions provided here do not fully account for result code
substitutions used to prevent unauthorized disclosures (such as
substitution of noSuchObject for insufficientAccessRights, or
invalidCredentials for insufficientAccessRights).
A.1. Non-Error Result Codes
These result codes (called "non-error" result codes) do not indicate
an error condition:
success (0),
compareFalse (5),
compareTrue (6),
referral (10), and
saslBindInProgress (14).
The success, compareTrue, and compareFalse result codes indicate
successful completion (and, hence, are referred to as "successful"
result codes).
The referral and saslBindInProgress result codes indicate the client
needs to take additional action to complete the operation.
A.2. Result Codes
Existing LDAP result codes are described as follows:
success (0)
Indicates the successful completion of an operation. Note:
this code is not used with the Compare operation. See
compareFalse (5) and compareTrue (6).
Sermersheim Standards Track [Page 49]
RFC 4511 LDAPv3 June 2006
operationsError (1)
Indicates that the operation is not properly sequenced with
relation to other operations (of same or different type).
For example, this code is returned if the client attempts to
StartTLS [RFC4346] while there are other uncompleted operations
or if a TLS layer was already installed.
protocolError (2)
Indicates the server received data that is not well-formed.
For Bind operation only, this code is also used to indicate
that the server does not support the requested protocol
version.
For Extended operations only, this code is also used to
indicate that the server does not support (by design or
configuration) the Extended operation associated with the
requestName.
For request operations specifying multiple controls, this may
be used to indicate that the server cannot ignore the order
of the controls as specified, or that the combination of the
specified controls is invalid or unspecified.
timeLimitExceeded (3)
Indicates that the time limit specified by the client was
exceeded before the operation could be completed.
sizeLimitExceeded (4)
Indicates that the size limit specified by the client was
exceeded before the operation could be completed.
compareFalse (5)
Indicates that the Compare operation has successfully
completed and the assertion has evaluated to FALSE or
Undefined.
compareTrue (6)
Indicates that the Compare operation has successfully
completed and the assertion has evaluated to TRUE.
authMethodNotSupported (7)
Indicates that the authentication method or mechanism is not
supported.
Sermersheim Standards Track [Page 50]
RFC 4511 LDAPv3 June 2006
strongerAuthRequired (8)
Indicates the server requires strong(er) authentication in
order to complete the operation.
When used with the Notice of Disconnection operation, this
code indicates that the server has detected that an
established security association between the client and
server has unexpectedly failed or been compromised.
referral (10)
Indicates that a referral needs to be chased to complete the
operation (see Section 4.1.10).
adminLimitExceeded (11)
Indicates that an administrative limit has been exceeded.
unavailableCriticalExtension (12)
Indicates a critical control is unrecognized (see Section
4.1.11).
confidentialityRequired (13)
Indicates that data confidentiality protections are required.
saslBindInProgress (14)
Indicates the server requires the client to send a new bind
request, with the same SASL mechanism, to continue the
authentication process (see Section 4.2).
noSuchAttribute (16)
Indicates that the named entry does not contain the specified
attribute or attribute value.
undefinedAttributeType (17)
Indicates that a request field contains an unrecognized
attribute description.
inappropriateMatching (18)
Indicates that an attempt was made (e.g., in an assertion) to
use a matching rule not defined for the attribute type
concerned.
constraintViolation (19)
Indicates that the client supplied an attribute value that
does not conform to the constraints placed upon it by the
data model.
For example, this code is returned when multiple values are
supplied to an attribute that has a SINGLE-VALUE constraint.
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RFC 4511 LDAPv3 June 2006
attributeOrValueExists (20)
Indicates that the client supplied an attribute or value to
be added to an entry, but the attribute or value already
exists.
invalidAttributeSyntax (21)
Indicates that a purported attribute value does not conform
to the syntax of the attribute.
noSuchObject (32)
Indicates that the object does not exist in the DIT.
aliasProblem (33)
Indicates that an alias problem has occurred. For example,
the code may used to indicate an alias has been dereferenced
that names no object.
invalidDNSyntax (34)
Indicates that an LDAPDN or RelativeLDAPDN field (e.g., search
base, target entry, ModifyDN newrdn, etc.) of a request does
not conform to the required syntax or contains attribute
values that do not conform to the syntax of the attribute's
type.
aliasDereferencingProblem (36)
Indicates that a problem occurred while dereferencing an
alias. Typically, an alias was encountered in a situation
where it was not allowed or where access was denied.
inappropriateAuthentication (48)
Indicates the server requires the client that had attempted
to bind anonymously or without supplying credentials to
provide some form of credentials.
invalidCredentials (49)
Indicates that the provided credentials (e.g., the user's name
and password) are invalid.
insufficientAccessRights (50)
Indicates that the client does not have sufficient access
rights to perform the operation.
busy (51)
Indicates that the server is too busy to service the
operation.
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RFC 4511 LDAPv3 June 2006
unavailable (52)
Indicates that the server is shutting down or a subsystem
necessary to complete the operation is offline.
unwillingToPerform (53)
Indicates that the server is unwilling to perform the
operation.
loopDetect (54)
Indicates that the server has detected an internal loop (e.g.,
while dereferencing aliases or chaining an operation).
namingViolation (64)
Indicates that the entry's name violates naming restrictions.
objectClassViolation (65)
Indicates that the entry violates object class restrictions.
notAllowedOnNonLeaf (66)
Indicates that the operation is inappropriately acting upon a
non-leaf entry.
notAllowedOnRDN (67)
Indicates that the operation is inappropriately attempting to
remove a value that forms the entry's relative distinguished
name.
entryAlreadyExists (68)
Indicates that the request cannot be fulfilled (added, moved,
or renamed) as the target entry already exists.
objectClassModsProhibited (69)
Indicates that an attempt to modify the object class(es) of
an entry's 'objectClass' attribute is prohibited.
For example, this code is returned when a client attempts to
modify the structural object class of an entry.
affectsMultipleDSAs (71)
Indicates that the operation cannot be performed as it would
affect multiple servers (DSAs).
other (80)
Indicates the server has encountered an internal error.
Sermersheim Standards Track [Page 53]
RFC 4511 LDAPv3 June 2006
Appendix B. Complete ASN.1 Definition
This appendix is normative.
Lightweight-Directory-Access-Protocol-V3 {1 3 6 1 1 18}
-- Copyright (C) The Internet Society (2006). This version of
-- this ASN.1 module is part of RFC 4511; see the RFC itself
-- for full legal notices.
DEFINITIONS
IMPLICIT TAGS
EXTENSIBILITY IMPLIED ::=
BEGIN
LDAPMessage ::= SEQUENCE {
messageID MessageID,
protocolOp CHOICE {
bindRequest BindRequest,
bindResponse BindResponse,
unbindRequest UnbindRequest,
searchRequest SearchRequest,
searchResEntry SearchResultEntry,
searchResDone SearchResultDone,
searchResRef SearchResultReference,
modifyRequest ModifyRequest,
modifyResponse ModifyResponse,
addRequest AddRequest,
addResponse AddResponse,
delRequest DelRequest,
delResponse DelResponse,
modDNRequest ModifyDNRequest,
modDNResponse ModifyDNResponse,
compareRequest CompareRequest,
compareResponse CompareResponse,
abandonRequest AbandonRequest,
extendedReq ExtendedRequest,
extendedResp ExtendedResponse,
...,
intermediateResponse IntermediateResponse },
controls [0] Controls OPTIONAL }
MessageID ::= INTEGER (0 .. maxInt)
maxInt INTEGER ::= 2147483647 -- (2^^31 - 1) --
LDAPString ::= OCTET STRING -- UTF-8 encoded,
-- [ISO10646] characters
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RFC 4511 LDAPv3 June 2006
LDAPOID ::= OCTET STRING -- Constrained to <numericoid>
-- [RFC4512]
LDAPDN ::= LDAPString -- Constrained to <distinguishedName>
-- [RFC4514]
RelativeLDAPDN ::= LDAPString -- Constrained to <name-component>
-- [RFC4514]
AttributeDescription ::= LDAPString
-- Constrained to <attributedescription>
-- [RFC4512]
AttributeValue ::= OCTET STRING
AttributeValueAssertion ::= SEQUENCE {
attributeDesc AttributeDescription,
assertionValue AssertionValue }
AssertionValue ::= OCTET STRING
PartialAttribute ::= SEQUENCE {
type AttributeDescription,
vals SET OF value AttributeValue }
Attribute ::= PartialAttribute(WITH COMPONENTS {
...,
vals (SIZE(1..MAX))})
MatchingRuleId ::= LDAPString
LDAPResult ::= SEQUENCE {
resultCode ENUMERATED {
success (0),
operationsError (1),
protocolError (2),
timeLimitExceeded (3),
sizeLimitExceeded (4),
compareFalse (5),
compareTrue (6),
authMethodNotSupported (7),
strongerAuthRequired (8),
-- 9 reserved --
referral (10),
adminLimitExceeded (11),
unavailableCriticalExtension (12),
confidentialityRequired (13),
saslBindInProgress (14),
Sermersheim Standards Track [Page 55]
RFC 4511 LDAPv3 June 2006
noSuchAttribute (16),
undefinedAttributeType (17),
inappropriateMatching (18),
constraintViolation (19),
attributeOrValueExists (20),
invalidAttributeSyntax (21),
-- 22-31 unused --
noSuchObject (32),
aliasProblem (33),
invalidDNSyntax (34),
-- 35 reserved for undefined isLeaf --
aliasDereferencingProblem (36),
-- 37-47 unused --
inappropriateAuthentication (48),
invalidCredentials (49),
insufficientAccessRights (50),
busy (51),
unavailable (52),
unwillingToPerform (53),
loopDetect (54),
-- 55-63 unused --
namingViolation (64),
objectClassViolation (65),
notAllowedOnNonLeaf (66),
notAllowedOnRDN (67),
entryAlreadyExists (68),
objectClassModsProhibited (69),
-- 70 reserved for CLDAP --
affectsMultipleDSAs (71),
-- 72-79 unused --
other (80),
... },
matchedDN LDAPDN,
diagnosticMessage LDAPString,
referral [3] Referral OPTIONAL }
Referral ::= SEQUENCE SIZE (1..MAX) OF uri URI
URI ::= LDAPString -- limited to characters permitted in
-- URIs
Controls ::= SEQUENCE OF control Control
Control ::= SEQUENCE {
controlType LDAPOID,
criticality BOOLEAN DEFAULT FALSE,
controlValue OCTET STRING OPTIONAL }
Sermersheim Standards Track [Page 56]
RFC 4511 LDAPv3 June 2006
BindRequest ::= [APPLICATION 0] SEQUENCE {
version INTEGER (1 .. 127),
name LDAPDN,
authentication AuthenticationChoice }
AuthenticationChoice ::= CHOICE {
simple [0] OCTET STRING,
-- 1 and 2 reserved
sasl [3] SaslCredentials,
... }
SaslCredentials ::= SEQUENCE {
mechanism LDAPString,
credentials OCTET STRING OPTIONAL }
BindResponse ::= [APPLICATION 1] SEQUENCE {
COMPONENTS OF LDAPResult,
serverSaslCreds [7] OCTET STRING OPTIONAL }
UnbindRequest ::= [APPLICATION 2] NULL
SearchRequest ::= [APPLICATION 3] SEQUENCE {
baseObject LDAPDN,
scope ENUMERATED {
baseObject (0),
singleLevel (1),
wholeSubtree (2),
... },
derefAliases ENUMERATED {
neverDerefAliases (0),
derefInSearching (1),
derefFindingBaseObj (2),
derefAlways (3) },
sizeLimit INTEGER (0 .. maxInt),
timeLimit INTEGER (0 .. maxInt),
typesOnly BOOLEAN,
filter Filter,
attributes AttributeSelection }
AttributeSelection ::= SEQUENCE OF selector LDAPString
-- The LDAPString is constrained to
-- <attributeSelector> in Section 4.5.1.8
Filter ::= CHOICE {
and [0] SET SIZE (1..MAX) OF filter Filter,
or [1] SET SIZE (1..MAX) OF filter Filter,
not [2] Filter,
equalityMatch [3] AttributeValueAssertion,
Sermersheim Standards Track [Page 57]
RFC 4511 LDAPv3 June 2006
substrings [4] SubstringFilter,
greaterOrEqual [5] AttributeValueAssertion,
lessOrEqual [6] AttributeValueAssertion,
present [7] AttributeDescription,
approxMatch [8] AttributeValueAssertion,
extensibleMatch [9] MatchingRuleAssertion,
... }
SubstringFilter ::= SEQUENCE {
type AttributeDescription,
substrings SEQUENCE SIZE (1..MAX) OF substring CHOICE {
initial [0] AssertionValue, -- can occur at most once
any [1] AssertionValue,
final [2] AssertionValue } -- can occur at most once
}
MatchingRuleAssertion ::= SEQUENCE {
matchingRule [1] MatchingRuleId OPTIONAL,
type [2] AttributeDescription OPTIONAL,
matchValue [3] AssertionValue,
dnAttributes [4] BOOLEAN DEFAULT FALSE }
SearchResultEntry ::= [APPLICATION 4] SEQUENCE {
objectName LDAPDN,
attributes PartialAttributeList }
PartialAttributeList ::= SEQUENCE OF
partialAttribute PartialAttribute
SearchResultReference ::= [APPLICATION 19] SEQUENCE
SIZE (1..MAX) OF uri URI
SearchResultDone ::= [APPLICATION 5] LDAPResult
ModifyRequest ::= [APPLICATION 6] SEQUENCE {
object LDAPDN,
changes SEQUENCE OF change SEQUENCE {
operation ENUMERATED {
add (0),
delete (1),
replace (2),
... },
modification PartialAttribute } }
ModifyResponse ::= [APPLICATION 7] LDAPResult
Sermersheim Standards Track [Page 58]
RFC 4511 LDAPv3 June 2006
AddRequest ::= [APPLICATION 8] SEQUENCE {
entry LDAPDN,
attributes AttributeList }
AttributeList ::= SEQUENCE OF attribute Attribute
AddResponse ::= [APPLICATION 9] LDAPResult
DelRequest ::= [APPLICATION 10] LDAPDN
DelResponse ::= [APPLICATION 11] LDAPResult
ModifyDNRequest ::= [APPLICATION 12] SEQUENCE {
entry LDAPDN,
newrdn RelativeLDAPDN,
deleteoldrdn BOOLEAN,
newSuperior [0] LDAPDN OPTIONAL }
ModifyDNResponse ::= [APPLICATION 13] LDAPResult
CompareRequest ::= [APPLICATION 14] SEQUENCE {
entry LDAPDN,
ava AttributeValueAssertion }
CompareResponse ::= [APPLICATION 15] LDAPResult
AbandonRequest ::= [APPLICATION 16] MessageID
ExtendedRequest ::= [APPLICATION 23] SEQUENCE {
requestName [0] LDAPOID,
requestValue [1] OCTET STRING OPTIONAL }
ExtendedResponse ::= [APPLICATION 24] SEQUENCE {
COMPONENTS OF LDAPResult,
responseName [10] LDAPOID OPTIONAL,
responseValue [11] OCTET STRING OPTIONAL }
IntermediateResponse ::= [APPLICATION 25] SEQUENCE {
responseName [0] LDAPOID OPTIONAL,
responseValue [1] OCTET STRING OPTIONAL }
END
Sermersheim Standards Track [Page 59]
RFC 4511 LDAPv3 June 2006
Appendix C. Changes
This appendix is non-normative.
This appendix summarizes substantive changes made to RFC 2251, RFC
2830, and RFC 3771.
C.1. Changes Made to RFC 2251
This section summarizes the substantive changes made to Sections 1,
2, 3.1, and 4, and the remainder of RFC 2251. Readers should
consult [RFC4512] and [RFC4513] for summaries of changes to other
sections.
C.1.1. Section 1 (Status of this Memo)
- Removed IESG note. Post publication of RFC 2251, mandatory LDAP
authentication mechanisms have been standardized which are
sufficient to remove this note. See [RFC4513] for authentication
mechanisms.
C.1.2. Section 3.1 (Protocol Model) and others
- Removed notes giving history between LDAP v1, v2, and v3. Instead,
added sufficient language so that this document can stand on its
own.
C.1.3. Section 4 (Elements of Protocol)
- Clarified where the extensibility features of ASN.1 apply to the
protocol. This change affected various ASN.1 types by the
inclusion of ellipses (...) to certain elements.
- Removed the requirement that servers that implement version 3 or
later MUST provide the 'supportedLDAPVersion' attribute. This
statement provided no interoperability advantages.
C.1.4. Section 4.1.1 (Message Envelope)
- There was a mandatory requirement for the server to return a
Notice of Disconnection and drop the transport connection when a
PDU is malformed in a certain way. This has been updated such that
the server SHOULD return the Notice of Disconnection, and it MUST
terminate the LDAP Session.
C.1.5. Section 4.1.1.1 (Message ID)
- Required that the messageID of requests MUST be non-zero as the
zero is reserved for Notice of Disconnection.
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RFC 4511 LDAPv3 June 2006
- Specified when it is and isn't appropriate to return an already
used messageID. RFC 2251 accidentally imposed synchronous server
behavior in its wording of this.
C.1.6. Section 4.1.2 (String Types)
- Stated that LDAPOID is constrained to <numericoid> from [RFC4512].
C.1.7. Section 4.1.5.1 (Binary Option) and others
- Removed the Binary Option from the specification. There are
numerous interoperability problems associated with this method of
alternate attribute type encoding. Work to specify a suitable
replacement is ongoing.
C.1.8. Section 4.1.8 (Attribute)
- Combined the definitions of PartialAttribute and Attribute here,
and defined Attribute in terms of PartialAttribute.
C.1.9. Section 4.1.10 (Result Message)
- Renamed "errorMessage" to "diagnosticMessage" as it is allowed to
be sent for non-error results.
- Moved some language into Appendix A, and referred the reader there.
- Allowed matchedDN to be present for other result codes than those
listed in RFC 2251.
- Renamed the code "strongAuthRequired" to "strongerAuthRequired" to
clarify that this code may often be returned to indicate that a
stronger authentication is needed to perform a given operation.
C.1.10. Section 4.1.11 (Referral)
- Defined referrals in terms of URIs rather than URLs.
- Removed the requirement that all referral URIs MUST be equally
capable of progressing the operation. The statement was ambiguous
and provided no instructions on how to carry it out.
- Added the requirement that clients MUST NOT loop between servers.
- Clarified the instructions for using LDAPURLs in referrals, and in
doing so added a recommendation that the scope part be present.
- Removed imperatives which required clients to use URLs in specific
ways to progress an operation. These did nothing for
interoperability.
Sermersheim Standards Track [Page 61]
RFC 4511 LDAPv3 June 2006
C.1.11. Section 4.1.12 (Controls)
- Specified how control values defined in terms of ASN.1 are to be
encoded.
- Noted that the criticality field is only applied to request
messages (except UnbindRequest), and must be ignored when present
on response messages and UnbindRequest.
- Specified that non-critical controls may be ignored at the
server's discretion. There was confusion in the original wording
which led some to believe that recognized controls may not be
ignored as long as they were associated with a proper request.
- Added language regarding combinations of controls and the ordering
of controls on a message.
- Specified that when the semantics of the combination of controls
is undefined or unknown, it results in a protocolError.
- Changed "The server MUST be prepared" to "Implementations MUST be
prepared" in paragraph 8 to reflect that both client and server
implementations must be able to handle this (as both parse
controls).
C.1.12. Section 4.2 (Bind Operation)
- Mandated that servers return protocolError when the version is not
supported.
- Disambiguated behavior when the simple authentication is used, the
name is empty, and the password is non-empty.
- Required servers to not dereference aliases for Bind. This was
added for consistency with other operations and to help ensure
data consistency.
- Required that textual passwords be transferred as UTF-8 encoded
Unicode, and added recommendations on string preparation. This was
to help ensure interoperability of passwords being sent from
different clients.
C.1.13. Section 4.2.1 (Sequencing of the Bind Request)
- This section was largely reorganized for readability, and language
was added to clarify the authentication state of failed and
abandoned Bind operations.
- Removed: "If a SASL transfer encryption or integrity mechanism has
been negotiated, that mechanism does not support the changing of
credentials from one identity to another, then the client MUST
instead establish a new connection."
If there are dependencies between multiple negotiations of a
particular SASL mechanism, the technical specification for that
SASL mechanism details how applications are to deal with them.
LDAP should not require any special handling.
- Dropped MUST imperative in paragraph 3 to align with [RFC2119].
Sermersheim Standards Track [Page 62]
RFC 4511 LDAPv3 June 2006
- Mandated that clients not send non-Bind operations while a Bind is
in progress, and suggested that servers not process them if they
are received. This is needed to ensure proper sequencing of the
Bind in relationship to other operations.
C.1.14. Section 4.2.3 (Bind Response)
- Moved most error-related text to Appendix A, and added text
regarding certain errors used in conjunction with the Bind
operation.
- Prohibited the server from specifying serverSaslCreds when not
appropriate.
C.1.15. Section 4.3 (Unbind Operation)
- Specified that both peers are to cease transmission and terminate
the LDAP session for the Unbind operation.
C.1.16. Section 4.4 (Unsolicited Notification)
- Added instructions for future specifications of Unsolicited
Notifications.
C.1.17. Section 4.5.1 (Search Request)
- SearchRequest attributes is now defined as an AttributeSelection
type rather than AttributeDescriptionList, and an ABNF is
provided.
- SearchRequest attributes may contain duplicate attribute
descriptions. This was previously prohibited. Now servers are
instructed to ignore subsequent names when they are duplicated.
This was relaxed in order to allow different short names and also
OIDs to be requested for an attribute.
- The present search filter now evaluates to Undefined when the
specified attribute is not known to the server. It used to
evaluate to FALSE, which caused behavior inconsistent with what
most would expect, especially when the 'not' operator was used.
- The Filter choice SubstringFilter substrings type is now defined
with a lower bound of 1.
- The SubstringFilter substrings 'initial, 'any', and 'final' types
are now AssertionValue rather than LDAPString. Also, added
imperatives stating that 'initial' (if present) must be listed
first, and 'final' (if present) must be listed last.
- Disambiguated the semantics of the derefAliases choices. There was
question as to whether derefInSearching applied to the base object
in a wholeSubtree Search.
- Added instructions for equalityMatch, substrings, greaterOrEqual,
lessOrEqual, and approxMatch.
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RFC 4511 LDAPv3 June 2006
C.1.18. Section 4.5.2 (Search Result)
- Recommended that servers not use attribute short names when it
knows they are ambiguous or may cause interoperability problems.
- Removed all mention of ExtendedResponse due to lack of
implementation.
C.1.19. Section 4.5.3 (Continuation References in the Search Result)
- Made changes similar to those made to Section 4.1.11.
C.1.20. Section 4.5.3.1 (Example)
- Fixed examples to adhere to changes made to Section 4.5.3.
C.1.21. Section 4.6 (Modify Operation)
- Replaced AttributeTypeAndValues with Attribute as they are
equivalent.
- Specified the types of modification changes that might
temporarily violate schema. Some readers were under the impression
that any temporary schema violation was allowed.
C.1.22. Section 4.7 (Add Operation)
- Aligned Add operation with X.511 in that the attributes of the RDN
are used in conjunction with the listed attributes to create the
entry. Previously, Add required that the distinguished values be
present in the listed attributes.
- Removed requirement that the objectClass attribute MUST be
specified as some DSE types do not require this attribute.
Instead, generic wording was added, requiring the added entry to
adhere to the data model.
- Removed recommendation regarding placement of objects. This is
covered in the data model document.
C.1.23. Section 4.9 (Modify DN Operation)
- Required servers to not dereference aliases for Modify DN. This
was added for consistency with other operations and to help ensure
data consistency.
- Allow Modify DN to fail when moving between naming contexts.
- Specified what happens when the attributes of the newrdn are not
present on the entry.
Sermersheim Standards Track [Page 64]
RFC 4511 LDAPv3 June 2006
C.1.24. Section 4.10 (Compare Operation)
- Specified that compareFalse means that the Compare took place and
the result is false. There was confusion that led people to
believe that an Undefined match resulted in compareFalse.
- Required servers to not dereference aliases for Compare. This was
added for consistency with other operations and to help ensure
data consistency.
C.1.25. Section 4.11 (Abandon Operation)
- Explained that since Abandon returns no response, clients should
not use it if they need to know the outcome.
- Specified that Abandon and Unbind cannot be abandoned.
C.1.26. Section 4.12 (Extended Operation)
- Specified how values of Extended operations defined in terms of
ASN.1 are to be encoded.
- Added instructions on what Extended operation specifications
consist of.
- Added a recommendation that servers advertise supported Extended
operations.
C.1.27. Section 5.2 (Transfer Protocols)
- Moved referral-specific instructions into referral-related
sections.
C.1.28. Section 7 (Security Considerations)
- Reworded notes regarding SASL not protecting certain aspects of
the LDAP Bind messages.
- Noted that Servers are encouraged to prevent directory
modifications by clients that have authenticated anonymously
[RFC4513].
- Added a note regarding the possibility of changes to security
factors (authentication, authorization, and data confidentiality).
- Warned against following referrals that may have been injected in
the data stream.
- Noted that servers should protect information equally, whether in
an error condition or not, and mentioned matchedDN,
diagnosticMessage, and resultCodes specifically.
- Added a note regarding malformed and long encodings.
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RFC 4511 LDAPv3 June 2006
C.1.29. Appendix A (Complete ASN.1 Definition)
- Added "EXTENSIBILITY IMPLIED" to ASN.1 definition.
- Removed AttributeType. It is not used.
C.2. Changes Made to RFC 2830
This section summarizes the substantive changes made to Sections of
RFC 2830. Readers should consult [RFC4513] for summaries of changes
to other sections.
C.2.1. Section 2.3 (Response other than "success")
- Removed wording indicating that referrals can be returned from
StartTLS.
- Removed requirement that only a narrow set of result codes can be
returned. Some result codes are required in certain scenarios, but
any other may be returned if appropriate.
- Removed requirement that the ExtendedResponse.responseName MUST be
present. There are circumstances where this is impossible, and
requiring this is at odds with language in Section 4.12.
C.2.1. Section 4 (Closing a TLS Connection)
- Reworded most of this section to align with definitions of the
LDAP protocol layers.
- Removed instructions on abrupt closure as this is covered in other
areas of the document (specifically, Section 5.3)
C.3. Changes Made to RFC 3771
- Rewrote to fit into this document. In general, semantics were
preserved. Supporting and background language seen as redundant
due to its presence in this document was omitted.
- Specified that Intermediate responses to a request may be of
different types, and one of the response types may be specified to
have no response value.
Sermersheim Standards Track [Page 66]
RFC 4511 LDAPv3 June 2006
Editor's Address
Jim Sermersheim
Novell, Inc.
1800 South Novell Place
Provo, Utah 84606, USA
Phone: +1 801 861-3088
EMail: jimse@novell.com
Sermersheim Standards Track [Page 67]
RFC 4511 LDAPv3 June 2006
Full Copyright Statement
Copyright (C) The Internet Society (2006).
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contained in BCP 78, and except as set forth therein, the authors
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Sermersheim Standards Track [Page 68]
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