RFC 4511
Lightweight Directory Access Protocol (LDAP): The Protocol
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.
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.
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.
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.
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,
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.
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.
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:
- 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.
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.
- 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.
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.
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.
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.
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)
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.
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
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
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] LDAPResult4.9. 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.
- 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.
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.
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 }
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),
- 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).
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.
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.
Protocol peers MAY terminate the LDAP session after sending or receiving a TLS closure alert.
(page 42 continued on part 3)
