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LDAPEXT Working Group J. Sermersheim
Internet Draft Novell, Inc
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LDAP Control for a Duplicate Entry Representation of Search Results
1. Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [1].
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts. Internet-Drafts are draft documents valid for a maximum of
six months and may be updated, replaced, or obsoleted by other
documents at any time. It is inappropriate to use Internet- Drafts
as reference material or to cite them other than as "work in
progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
2. Abstract
This document describes a Duplicate Entry Representation control
extension for the LDAP Search operation. By using the control with
an LDAP search, a client requests that the server return separate
entries for each value held in the specified attributes. For
instance, if a specified attribute of an entry holds multiple
values, the search operation will return multiple instances of that
entry, each instance holding a separate single value in that
attribute.
3. Overview
The Server-Side Sorting control [RFC2891] allows the server to order
search result entries based on attribute values (sort keys). It
does not allow one to specify behavior when an attribute contains
multiple values. The default behavior, as outlined in 7.9 of
[X.511], is to use the smallest value as the sort key.
An application may need to produce an ordered list of entries,
sorted by a multi-valued attribute, where each attribute value is
represented in the list. In order to do this, a separate control is
needed which causes the set of entries to be expanded sufficiently
to represent each attribute value prior to sorting.
LDAP Control for a Duplicate Entry Representation of Search Results
This document describes controls, which allow duplicate entries in
the result set of search, where each entry represents a distinct
value of a given multiple valued attribute.
An example of this would be a sorted list of all telephone numbers
in an organization. Because any entry may have multiple telephone
numbers, and the list is to be sorted by telephone number, the list
must be able to contain duplicate entries, each with its own unique
telephone number.
Another example would be an application that needs to display an
ordered list of all members of a group. It would use this control
to create a result set of duplicate groupOfNames entries, each with
a single, unique value in its member attribute.
The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
used in this document carry the meanings described in [RFC2119].
4. The Controls
Support for the controls is advertised by the presence of their OID
in the supportedControl attribute of a server's root DSE. The OID
for the request control is "2.16.840.1.113719.1.27.101.1" and the
OIDs for the response controls are "2.16.840.1.113719.1.27.101.2"
and "2.16.840.1.113719.1.27.101.3".
4.1 Request Control
This control is included in the searchRequest message as part of the
controls field of the LDAPMessage, as defined in Section 4.1.12 of
The controlType is set to "2.16.840.1.113719.1.27.101.1". The
criticality MAY be set to either TRUE or FALSE. The controlValue is
an OCTET STRING, whose value is the BER encoding of the following
type:
DuplicateEntryRequest ::= SEQUENCE {
AttributeDescriptionList, -- from [RFC2251]
PartialApplicationAllowed BOOLEAN DEFAULT TRUE }
4.1.1 AttributeDescriptionList Semantics
The AttributeDescriptionList data type is described in 4.1.5 of
[RFC2251] and describes a list of zero or more AttributeDescription
types as also described in 4.1.5 of [RFC2251]. Both definitions are
repeated here for convenience:
AttributeDescriptionList ::= SEQUENCE OF
AttributeDescription
LDAP Control for a Duplicate Entry Representation of Search Results
A value of AttributeDescription is based on the following BNF:
attributeDescription = AttributeType [ ";" <options> ]
While processing a search request, a server implementation examines
this list. If a specified attribute or attribute subtype exists in
an entry to be returned by search, and that attribute holds multiple
values, the server treats the entry as if it were multiple,
duplicate entries -- the specified attributes each holding a single,
unique value from the original set of values of that attribute.
Client implementations SHOULD NOT specify attribute type options
number of duplicate entries is the combination of all values in each
attribute. Because of the potential complexity involved in servicing
multiple attributes, server implementations MAY choose to support a
limited number of attributes in the control.
There is a special case where either no attributes are specified, or
an attribute description value of "*" is specified. In this case,
all attributes are used. (The "*" allows the client to request all
user attributes in addition to specific operational attributes).
If an attribute is unrecognized, that attribute is ignored when
processing the control.
4.1.2 PartialApplicationAllowed Semantics
The PartialApplicationAllowed field is used to specify whether the
client will allow the server to apply this control to a subset of
the search result set. If TRUE, the server is free to arbitrarily
apply this control to no, any, or all search results. If FALSE, the
server MUST either apply the control to all search results or fail
to support the control at all.
Client implementations use the DuplicateSearchResult control to
discover which search results have been affected by this control
4.2 Response Controls
Two response controls are defined to provide feedback while the
search results are being processed; DuplicateSearchResult and
DuplicateEntryResponseDone.
The DuplicateSearchResult control is sent with all SearchResultEntry
operations that contain search results which have been modified by
the DuplicateEntryRequest control.
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LDAP Control for a Duplicate Entry Representation of Search Results
The DuplicateEntryResponseDone control is sent with the
SearchResultDone operation in order to convey completion
information.
4.2.1 The DuplicateSearchResult control
This control is included in the SearchResultEntry message of any
search result that holds an entry that has been modified by the
DuplicateEntryRequest control as part of the controls field of the
LDAPMessage, as defined in Section 4.1.12 of [RFC2251]. This control
is absent on search results that are unaffected by
DuplicateEntryRequest control.
The controlType is set to "2.16.840.1.113719.1.27.101.2". The
criticality is ignored. The controlValue is not included.
4.2.2 The DuplicateEntryResponseDone control
This control is included in the searchResultDone message as part of
the controls field of the LDAPMessage, as defined in Section 4.1.12
The controlType is set to "2.16.840.1.113719.1.27.101.3". The
criticality is ignored. The controlValue is an OCTET STRING, whose
value is the BER encoding of the following SEQUENCE:
DuplicateEntryResponseDone ::= SEQUENCE {
resultCode, -- From [RFC2251]
errorMessage [0] LDAPString OPTIONAL,
A result field is provided here to allow the server to convey to the
client that an error resulted due to the control being serviced. For
example, a search that would ordinarily complete successfully may
fail with a sizeLimitExceeded error due to this control being
processed.
Though any result code that is defined in [RFC2251] MAY be returned
the following list assigns special meanings to certain result codes
when returned in this control:
- success: The control was successful.
- timeLimitExceeded Time limit reached before attribute values
could be processed.
- sizeLimitExceeded Size limit reached as a result of this
control.
- adminLimitExceeded result set too large for server to handle.
- unwillingToPerform Server cannot process control.
errorMessage MAY be populated with a human-readable string in the
event of an erroneous result code.
LDAP Control for a Duplicate Entry Representation of Search Results
attribute MAY be set to the value of the first attribute specified
by the DuplicateEntryRequest that was in error. The client MUST
ignore the attribute field if the result is success.
5. Protocol Examples
5.1 Simple example
This example will show this control being used to produce a list of
all telephone numbers in the dc=example,dc=net container. Let's say
the following three entries exist in this container;
telephoneNumber: 555-8854
telephoneNumber: 555-4588
telephoneNumber: 555-5884
telephoneNumber: 555-9425
telephoneNumber: 555-7992
First an LDAP search is specified with a baseDN of
"dc=example,dc=net", subtree scope, filter set to
"(telephoneNumber=*)". A DuplicateEntryRequest control is attached
to the search, specifying "telephoneNumber" as the attribute
The set of search results returned by the server would then consist
of the following entries:
LDAP Control for a Duplicate Entry Representation of Search Results
All but the first entry are accompanied by the DuplicateSearchResult
control when sent from the server.
Note that it is not necessary to use an attribute in this control
that is specified in the search filter. This example only does so,
because the result was to obtain a list of telephone numbers.
5.2 Specifying multiple attributes
A more complicated example involving multiple attributes will result
in more entries. If we assume these entries in the directory:
dn: cn=User1,dc=example,dc=net
givenName: User1
mail: user1@example.net
dn: cn=User2,dc=example,dc=net
givenName: User2
givenName: User Two
mail: user2@example.net
mail: usertwo@example.net
And both "mail" and "givenName" are specified as attributes in this
control, the resulting set of entries would be this:
dn: cn=User1,dc=example,dc=net
givenName: User1
mail: user1@example.net
dn: cn=User2,dc=example,dc=net
givenName: User2
mail: user2@example.net
dn: cn=User2,dc=example,dc=net
givenName: User2
mail: usertwo@example.net
dn: cn=User2,dc=example,dc=net
givenName: User Two
mail: user2@example.net
dn: cn=User2,dc=example,dc=net
givenName: User Two
mail: usertwo@example.net
LDAP Control for a Duplicate Entry Representation of Search Results
5.3 Listing the members of a groupOfNames
This example shows how the controls can be used to turn a single
groupOfNames entry into multiple duplicate entries. Let's say this
is our groupOfNames entry:
dn: cn=Administrators,dc=example,dc=net
cn: Administrators
member: cn=aBaker,dc=example,dc=net
member: cn=cDavis,dc=example,dc=net
member: cn=bChilds,dc=example,dc=net
member: cn=dEvans,dc=example,dc=net
We could set our search base to "cn=Administrators,dc=example,dc=net
", filter to "(objectClass=*)", use an object scope (to restrict it
to this entry) and send the duplicateEntryRequest control with
"member" as its attribute value. The resulting set would look like
this:
dn: cn=Administrators,dc=example,dc=net
member: cn=aBaker,dc=example,dc=net
dn: cn=Administrators,dc=example,dc=net
member: cn=cDavis,dc=example,dc=net
dn: cn=Administrators,dc=example,dc=net
member: cn=bChilds,dc=example,dc=net
dn: cn=Administrators,dc=example,dc=net
member: cn=dEvans,dc=example,dc=net
This list can then be sorted by member and displayed (also by
member) in a list.
6 Relationship to other controls
This control is intended (but not limited) to be used with the
Server Side Sorting control [RFC2891]. By pairing this control with
the Server Side Sorting control, One can produce a set of entries,
sorted by attribute values, where each attribute value is
represented in the sorted set. Server implementations MUST ensure
that this control is processed before sorting the result of a
search, as this control alters the result set of search.
control (which has a dependency on the Server Side Sort control).
The nature of the dependency between the VLV control and the Sort
control is such that the Sorting takes place first. Because the sort
happens first, and because this control is processed before the sort
Sermersheim Internet-Draft - Expires Jan 2001 Page 7
LDAP Control for a Duplicate Entry Representation of Search Results
control, the impact of this control on the VLV control is minimal.
Some server implementations may need to carefully consider how to
handle the typedown functionality of the VLV control when paired
with this control. The details of this are heavily implementation
dependent and are beyond the scope of this document.
7. Notes for Implementers
Both client and server implementations MUST be aware that using this
control could potentially result in a very large set of search
results. Servers MAY return an adminLimitExceeded result in the
response control due to inordinate consumption of resources. This
may be due to some a priori knowledge such as a server restriction
of the number of attribute in the request control that it's willing
to service, or it may be due to the server attempting to service the
control and running out of resources.
Client implementations MUST be aware that when using this control,
search entries returned will contain a subset of the values of any
If this control is used in a chained environment, servers SHOULD NOT
pass this control to other servers. Instead they SHOULD gather
results and apply this control themselves.
8. Security Considerations
This control allows finer control of the result set returned by an
LDAP search operation and as such may be used in a denial of service
attack. See Section 7 for more information on how this is detected
and handled.
9. Acknowledgments
The author gratefully thanks the input and support of participants
of the LDAP-EXT working group.
Wahl, M, S. Kille and T. Howes, "Lightweight Directory Access
Protocol (v3)", Internet RFC, December, 1997.
Available as RFC 2251.
Wahl, M, A. Herron and T. Howes, "LDAP Control Extension for Server
Side Sorting of Search Results", Internet RFC, August, 2000.
Available as RFC 2891.
[VLV]
Boreham, D, Sermersheim, J, Anantha, A, Armijo, M, "LDAP Extensions
for Scrolling View Browsing of Search Results", Internet Draft,
Sermersheim Internet-Draft - Expires Jan 2001 Page 8
LDAP Control for a Duplicate Entry Representation of Search Results
[X.511]
ITU-T Rec. X.511, "The Directory: Abstract Service Definition",
1993.
Bradner, Scott, "Key Words for use in RFCs to Indicate Requirement
Levels", Internet Draft, March, 1997.
Provo, Utah 84606, USA
jimse@novell.com
+1 801 861-3088