3 INTERNET-DRAFT R. Harrison
4 draft-rharrison-ldap-intermediate-resp-01.txt Novell, Inc.
5 Updates: 2251 K. Zeilenga
6 Intended Category: Standards Track OpenLDAP Foundation
10 The Lightweight Directory Access Protocol (LDAP)
11 Intermediate Response Message
16 This document is an Internet-Draft and is in full conformance with
17 all provisions of Section 10 of RFC2026.
19 This document is intended to be, after appropriate review and
20 revision, submitted to the RFC Editor as a Standard Track document.
22 Distribution of this memo is unlimited. Technical discussion of
23 this document will take place on the IETF LDAP Extensions Working
24 Group (ldapext) mailing list <ietf-ldapext@netscape.com>. Please
25 send editorial comments directly to the document editor
26 <roger_harrison@novell.com>
28 Internet-Drafts are working documents of the Internet Engineering
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30 other groups may also distribute working documents as Internet-
31 Drafts. Internet-Drafts are draft documents valid for a maximum of
32 six months and may be updated, replaced, or obsoleted by other
33 documents at any time. It is inappropriate to use Internet-Drafts
34 as reference material or to cite them other than as "work in
37 The list of current Internet-Drafts can be accessed at
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39 The list of Internet-Draft Shadow Directories can be accessed at
40 http://www.ietf.org/shadow.html.
44 Copyright (C) The Internet Society (2003). All Rights Reserved.
48 The Lightweight Directory Access Protocol (LDAP) version 3 is a
49 client-request/server-response based protocol. With the exception
50 of the search operation, the entire response to an operation request
51 is returned in a single LDAP message. While this single-
52 request/single-response paradigm is sufficient for many operations
53 (including all but one of those currently defined by LDAP), both
54 intuition and practical experience validate the notion that it is
55 insufficient for some operations. When multiple messages are sent
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63 in response to a single request, all but the last of these response
64 messages are referred to as "intermediate responses".
66 This document defines and describes the IntermediateResponse
67 message, a general mechanism for defining single-request/multiple-
68 response operations in LDAP. The IntermediateResponse message is
69 defined in a way that maintains the protocol behavior of existing
70 LDAP operations. This message is intended to be used in conjunction
71 with the LDAP ExtendedRequest and ExtendedResponse to define new
72 single-request/multiple-response operations or in conjunction with a
73 control when extending existing LDAP operations in a way that
74 requires them to return intermediate response information.
78 The Lightweight Directory Access Protocol (LDAP), version 3
79 [RFC3377] is an extensible protocol. Extended operations ([RFC2251]
80 Section 4.12) are defined to allow operations to be added to LDAP
81 without requiring a new revision of the protocol. Similarly,
82 controls ([RFC2251] section 4.1.12) are defined to extend or modify
83 the behavior of existing LDAP operations.
85 LDAP is a client-request/server-response based protocol. With the
86 exception of the search operation, the entire response to an
87 operation request is returned in a single protocol data unit (i.e.
88 LDAP message). While this single-request/single-response paradigm
89 is sufficient for many operations (including all but one of those
90 currently defined by [RFC3377]), both intuition and practical
91 experience validate the notion that it is insufficient for some
94 For example, the LDAP delete operation could be extended via a
95 subtree control to mean that an entire subtree is to be deleted. A
96 subtree delete operation needs to return continuation references
97 based upon subordinate knowledge information contained in the server
98 so that the client can complete the operation. Returning references
99 as they are found instead of with the final result allows the client
100 to progress the operation more efficiently because it does not have
101 to wait for the final result to get this continuation reference
104 Similarly, an engineer might choose to design the subtree delete
105 operation as an extended operation of its own rather than using a
106 subtree control in conjunction with the delete operation. Once
107 again, the same continuation reference information is needed by the
108 client to complete the operation, and sending the continuation
109 references as they are found would allow the client progress the
110 operation more efficiently.
112 Operations that complete in stages or that progress through various
113 states as they complete might want to send intermediate responses to
114 the client, thereby informing it of the status of the operation.
115 For example, an LDAP implementation might define an extended
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122 operation to create a new replica of an administrative area on a
123 server, and the operation completes in three stages: (1) begin
124 creation of replica, (2) send replica data to server, (3) replica
125 creation complete. Intermediate messages might be sent from the
126 server to the client at the beginning of each stage with the final
127 response for the extended operation being sent after stage (3) is
130 As LDAP [RFC3377] is currently defined, there is no general LDAP
131 message type that can be used to return intermediate results. A
132 single, reusable LDAP message for carrying intermediate response
133 information is desired to avoid repeated modification of the
134 protocol. Although the ExtendedResponse message is defined in LDAP,
135 it is defined to be the one and only response message to an
136 ExtendedRequest message ([RFC2251] Section 4.12), for unsolicited
137 responses (LDAP Section 4.4), and to return intermediate responses
138 for the search operation ([RFC3377] Section 4.5.2, also see Section
139 5 below). The adaptation of ExtendedResponse as a general
140 intermediate response mechanism would be problematic. In
141 particular, existing APIs would likely have to be redesigned. It is
142 believed (based upon operational experience) that the addition of a
143 new message to carry intermediate result information is easier to
144 implement and is less likely to cause interoperability problems with
145 existing deployed implementations.
147 This document defines and describes the LDAP IntermediateResponse
148 message. This message is intended to be used in conjunction with
149 ExtendedRequest and ExtendedResponse to define new single-
150 request/multiple-response operations or in conjunction with a
151 control when extending existing LDAP operations in a way that
152 requires them to return intermediate response information.
154 It is intended that the definitions and descriptions of extended
155 operations and controls that make use of the IntermediateResponse
156 message will define the circumstances when an IntermediateResponse
157 message can be sent by a server and the associated meaning of an
158 IntermediateResponse message sent in a particular circumstance.
159 Similarly, it is intended that clients will explicitly solicit
160 IntermediateResponse messages by issuing operations that
161 specifically call for their return.
163 The LDAP Content Sync Operation [draft-zeilenga-ldup-sync] (a work
164 in progress) demonstrates one use of LDAP Intermediate Response
167 2. Conventions used in this document
169 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
170 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
171 document are to be interpreted as described in [RFC2119].
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181 The term "request control" is used to describe a control that is
182 included in an LDAP request message sent from an LDAP client to an
185 3. The IntermediateResponse Message
187 This document extends the protocolOp CHOICE of LDAPMessage
188 ([RFC2251] Section 4.1.1) to include the field:
190 intermediateResponse IntermediateResponse
192 where IntermediateResponse is defined as:
194 IntermediateResponse ::= [APPLICATION 25] SEQUENCE {
195 responseName [0] LDAPOID OPTIONAL,
196 responseValue [1] OCTET STRING OPTIONAL }
198 IntermediateResponse messages SHALL NOT be returned to the client
199 unless the client issues a request that specifically solicits their
200 return. This document defines two forms of solicitation: extended
201 operation and request control.
203 Although the responseName and responseValue are optional in some
204 circumstances, generally speaking IntermediateResponse messages have
205 a predefined responseName and a responseValue. The value of the
206 responseName (if present), the syntax of the responseValue (if
207 present) and the semantics associated with a particular
208 IntermediateResponse message MUST be specified in documents
209 describing the extended operation or request control that uses them.
210 Sections 3.1 and 3.2 describe additional requirements on the
211 inclusion of responseName and responseValue in IntermediateResponse
214 3.1. Usage with LDAP ExtendedRequest and ExtendedResponse
216 A single-request/multiple-response operation may be defined using a
217 single ExtendedRequest message to solicit zero or more
218 IntermediateResponse messages of one or more kinds followed by an
219 ExtendedResponse message.
221 An extended operation that defines the return of multiple kinds of
222 IntermediateResponse messages MUST provide and document a mechanism
223 for the client to distinguish the kind of IntermediateResponse
224 message being sent. This SHALL be accomplished by using different
225 responseName values for each type of IntermediateResponse message
226 associated with the extended operation or by including identifying
227 information in the responseValue of each type of
228 IntermediateResponse message associated with the extended operation.
230 3.2. Usage with LDAP Request Controls
232 Any LDAP operation may be extended by the addition of one or more
233 controls ([RFC2251] Section 4.1.12). A control's semantics may
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240 include the return of zero or more IntermediateResponse messages
241 prior to returning the final result code for the operation. One or
242 more kinds of IntermediateResponse messages may be sent in response
243 to a request control.
245 All IntermediateResponse messages associated with request controls
246 SHALL include a responseName. This requirement ensures that the
247 client can correctly identify the source of IntermediateResponse
250 (a) two or more controls using IntermediateResponse messages
251 are included in a request for any LDAP operation or
253 (b) one or more controls using IntermediateResponse messages
254 are included in a request with an LDAP extended
255 operation that uses IntermediateResponse messages.
257 A request control that defines the return of multiple kinds of
258 IntermediateResponse messages MUST provide and document a mechanism
259 for the client to distinguish the kind of IntermediateResponse
260 message being sent. This SHALL be accomplished by using different
261 responseName values for each type of IntermediateResponse message
262 associated with the request control or by including identifying
263 information in the responseValue of each type of
264 IntermediateResponse message associated with the request control.
266 4. Advertising Support for IntermediateResponse Messages
268 Because IntermediateResponse messages are associated with extended
269 operations or controls and LDAP provides a means for advertising the
270 extended operations and controls supported by a server (using the
271 supportedExtensions and supportedControls attributes of the root DSE
272 attributes), no separate means for advertising support for
273 IntermediateResponse messages is needed (or provided).
275 5. Use of IntermediateResponse and ExtendedResponse with Search
277 It is noted that ExtendedResponse messages may be sent in response
278 to LDAP search operations with controls ([RFC2251] Section 4.5.1).
279 This use of ExtendedResponse messages SHOULD be viewed as deprecated
280 in favor of use of the IntermediateResponse messages.
282 6. Security Considerations
284 This document describes an enhancement to LDAP. All security
285 considerations of [RFC3377] apply to this document, however it does
286 not introduce any new security considerations to LDAP.
288 Security considerations specific to each extension using this
289 protocol mechanism shall be discussed in the technical specification
290 detailing the extension.
292 7. IANA Considerations
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300 Registration of the following value is requested [RFC3383].
302 7.1. LDAP Message Type
304 It is requested that IANA register upon Standards Action an LDAP
305 Message Type to identify the LDAP IntermediateResponse message as
306 defined in section 3 of this document.
309 The following registration template is suggested:
311 Subject: Request for LDAP Message Type Registration
312 Person & email address to contact for further information:
313 Roger Harrison <roger_harrison@novell.com>
314 Specification: RFCXXXX
315 Author/Change Controller: IESG
316 Comments: Identifies the LDAP IntermediateResponse Message
320 The authors would like to acknowledge the members of the IETF LDAP
321 Extensions (ldapext) working group mail list who responded to the
322 suggestion that a multiple-response paradigm might be useful for
323 LDAP extended requests. Special thanks go to two individuals: David
324 Wilbur who first introduced the idea on the working group list, and
325 Thomas Salter, who succinctly summarized the group's discussion.
330 Bradner, S., "Key Words for use in RFCs to Indicate Requirement
331 Levels", BCP 14, RFC 2119, March 1997.
334 Wahl, M., Howes, T., and S. Kille, "Lightweight Directory
335 Access Protocol (v3)", RFC 2251, December 1997.
338 Hodges, J. and R. Morgan, "Lightweight Directory Access
339 Protocol (v3): Technical Specification", RFC 3377, September
343 Zeilenga, K., "Internet Assigned Numbers Authority (IANA)
344 Considerations for the Lightweight Directory Access Protocol
345 (LDAP)", RFC 3383, September 2002.
347 Informative References
349 [draft-zeilenga-ldup-sync]
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358 Zeilenga, K., "LDAP Content Synchronization Operation", Work in
368 roger_harrison@novell.com
375 Full Copyright Statement
377 "Copyright (C) The Internet Society (date). All Rights Reserved.
378 This document and translations of it may be copied and furnished to
379 others, and derivative works that comment on or otherwise explain it
380 or assist in its implementation may be prepared, copied, published
381 and distributed, in whole or in part, without restriction of any
382 kind, provided that the above copyright notice and this paragraph
383 are included on all such copies and derivative works. However, this
384 document itself may not be modified in any way, such as by removing
385 the copyright notice or references to the Internet Society or other
386 Internet organizations, except as needed for the purpose of
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389 followed, or as required to translate it into languages other than
392 The limited permissions granted above are perpetual and will not be
393 revoked by the Internet Society or its successors or assigns.
395 This document and the information contained herein is provided on an
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397 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
398 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
399 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
400 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
402 Appendix A - Document Revision History
403 Editors' Note: this appendix should be removed prior to publication
404 as an RFC. It is provided as an aid to reviewers of this "work in
407 A.1. draft-rharrison-ldap-extPartResp-00.txt
409 Initial revision of draft.
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417 A.2. draft-rharrison-ldap-extPartResp-01.txt
419 Changed responseName to be optional to align with [RFC3377]
420 definition of ExtendedResponse.
422 A.3. draft-rharrison-ldap-extPartResp-02.txt
424 Minor terminology corrections. Clarified use of
425 ExtendedPartialResponse with LDAP extended operations and other LDAP
426 operations with controls.
428 A.4. draft-rharrison-ldap-intermediateResp-00.txt
430 - Changed name of ExtendedPartialResponse to IntermediateResponse.
432 - Retitled "Motivation" section to "Background and Intended Usage"
433 and expanded its contents.
435 - Added detail surrounding the use of the IntermediateResponse with
436 extended operations and request controls.
438 - Generalized the way that Intermediate response fits into the ASN.1
441 - Added information on advertising IntermediateResponse.
443 - Added information on the use of IntermediateResponse with the
446 A.5. draft-rharrison-ldap-intermediateResp-01.txt
448 This draft was oriented primarily to preparing the draft for
449 publication in accordance with established RFC formatting
450 guidelines. No substantial change in overall content was made.
451 Changes included the following:
457 - Retitled "Background and Intended Usage" section to "Introduction"
458 and expanded its contents.
460 - Retitled Section 3 from "The Intermediate Response PDU" to "The
461 Intermediate Response Message".
463 - Renamed references to [RFCnnnn] format
465 - Added IANA Considerations section
467 - Retitled "References" section to "Normative References"
469 - Other small edits to bring draft in line with RFC formatting
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