Information technology — Open systems interconnection — Part 9: The Directory: Replication

This document specifies a shadow service which Directory system agents (DSAs) may use to replicate Directory information. The service allows Directory information to be replicated among DSAs to improve service to Directory users. The shadowed information is updated, using the defined protocol, thereby improving the service provided to users of the Directory.

Technologies de l'information — Interconnexion de systèmes ouverts (OSI) — Partie 9: Titre manque

General Information

Status
Published
Publication Date
30-Nov-2020
Current Stage
6060 - International Standard published
Start Date
09-Nov-2020
Completion Date
01-Dec-2020
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INTERNATIONAL ISO/IEC
STANDARD 9594-9
Eighth edition
Information technology — Open
systems interconnection —
Part 9:
The Directory: Replication
PROOF/ÉPREUVE
Reference number
ISO/IEC 9594-9:2020(E)
ISO/IEC 2020
---------------------- Page: 1 ----------------------
ISO/IEC 9594-9:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii PROOF/ÉPREUVE © ISO/IEC 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/IEC 9594-9:2020(E)
Foreword

ISO (the International Organization for Standardization) and IEC (the International Electrotechnical

Commission) form the specialized system for worldwide standardization. National bodies that are

members of ISO or IEC participate in the development of International Standards through technical

committees established by the respective organization to deal with particular fields of technical activity.

ISO and IEC technical committees collaborate in fields of mutual interest. Other international

organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the

work.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of document should be noted (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights. Details

of any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents) or the IEC list of patent

declarations received (see http://patents.iec.ch).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the World

Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT),
see www.iso.org/iso/foreword.html.

This document was prepared by ITU-T as ITU-T X.525 (10/2019) and drafted in accordance with its

editorial rules. It was adopted by Joint Technical Committee ISO/IEC JTC 1, Information technology,

Subcommittee SC 6, Telecommunications and information exchange between systems.
A list of all parts in the ISO/IEC 9594 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
© ISO/IEC 2020 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/IEC 9594-9:2020 (E)
CONTENTS
Page

1 Scope .............................................................................................................................................................. 1

2 Normative references...................................................................................................................................... 1

2.1 Identical Recommendations | International Standards ........................................................................ 1

3 Definitions ...................................................................................................................................................... 1

3.1 Basic Directory definitions .................................................................................................................. 1

3.2 Directory model definitions ................................................................................................................ 2

3.3 Abstract service definitions ................................................................................................................. 2

3.4 Distributed operation definitions ......................................................................................................... 2

3.5 Protocol definitions ............................................................................................................................. 2

3.6 Replication definitions ........................................................................................................................ 2

4 Abbreviations ................................................................................................................................................. 3

5 Conventions .................................................................................................................................................... 3

6 Replication in the Directory ........................................................................................................................... 4

6.1 Caching ............................................................................................................................................... 4

6.2 Shadowing ........................................................................................................................................... 4

6.3 Shadowing functional model ............................................................................................................... 5

7 Shadowing in the Directory ............................................................................................................................ 6

7.1 Shadowing agreement ......................................................................................................................... 6

7.2 Shadowed information ........................................................................................................................ 7

7.3 Shadow operations .............................................................................................................................. 10

7.4 DSA Shadow Bind and DSA Shadow Unbind operation .................................................................... 11

8 Shadow operational binding ........................................................................................................................... 11

8.1 Shadow operational binding type characteristics ................................................................................ 11

8.2 DSA procedures for operational binding management ....................................................................... 12

8.3 Operational binding ............................................................................................................................. 13

9 Shadowing agreement .................................................................................................................................... 14

9.1 Shadowing agreement specification .................................................................................................... 14

9.2 Unit of replication ............................................................................................................................... 15

9.3 Update mode ....................................................................................................................................... 20

10 Directory information shadow service............................................................................................................ 21

10.1 Shadow supplier initiated service ........................................................................................................ 21

10.2 Shadow consumer initiated service ..................................................................................................... 22

11 Shadow operations ......................................................................................................................................... 22

11.1 Coordinate Shadow Update operation ................................................................................................. 22

11.2 Request Shadow Update operation ...................................................................................................... 24

11.3 Update Shadow operation ................................................................................................................... 26

12 Shadow error .................................................................................................................................................. 30

12.1 Shadow error problems ....................................................................................................................... 30

12.2 Last update .......................................................................................................................................... 31

12.3 Update window ................................................................................................................................... 31

12.4 Common results .................................................................................................................................. 31

Annex A – Directory shadow abstract service in ASN.1 ........................................................................................... 32

Annex B – Amendments and corrigenda ................................................................................................................... 38

© ISO/IEC 2020 – All rights reserved
Rec. ITU-T X.525 (10/2019) v
---------------------- Page: 4 ----------------------
ISO/IEC 9594-9:2020 (E)
Introduction

This Recommendation | International Standard, together with other Recommendations | International Standards, has been

produced to facilitate the interconnection of information processing systems to provide Directory services. A set of such

systems, together with the Directory information that they hold, can be viewed as an integrated whole, called the

Directory. The information held by the Directory, collectively known as the Directory Information Base (DIB) is typically

used to facilitate communication between, with or about objects such as application-entities, people, terminals and

distribution lists.

The Directory plays a significant role in Open Systems Interconnection, whose aim is to allow, with a minimum of

technical agreement outside of the interconnection standards themselves, the interconnection of information processing

systems:
– from different manufacturers;
– under different managements;
– of different levels of complexity; and
– of different ages.

This Recommendation | International Standard defines the replication capabilities provided by Directory system agents

(DSAs) to improve the level of service to Directory users.

This Recommendation | International Standard provides the foundation frameworks upon which industry profiles can be

defined by other standards groups and industry forums. Many of the features defined as optional in these frameworks may

be mandated for use in certain environments through profiles. This ninth edition technically revises and enhances the

eighth edition of this Recommendation | International Standard.

Annex A, which is an integral part of this Recommendation | International Standard, provides the ASN.1 module for the

Directory shadow abstract service.

Annex B, which is not an integral part of this Recommendation | International Standard, lists the amendments and defect

reports that have been incorporated to form this edition of this Recommendation | International Standard.

© ISO/IEC 2020 – All rights reserved
vi Rec. ITU-T X.525 (10/2019)
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ISO/IEC 9594-9:2020 (E)
INTERNATIONAL STANDARD
ITU-T RECOMMENDATION

Information technology – Open Systems Interconnection – The Directory: Replication

1 Scope

This Recommendation | International Standard specifies a shadow service which Directory system agents (DSAs) may

use to replicate Directory information. The service allows Directory information to be replicated among DSAs to improve

service to Directory users. The shadowed information is updated, using the defined protocol, thereby improving the

service provided to users of the Directory.
2 Normative references

The following Recommendations and International Standards contain provisions which, through reference in this text,

constitute provisions of this Recommendation | International Standard. At the time of publication, the editions indicated

were valid. All Recommendations and Standards are subject to revision, and parties to agreements based on this

Recommendation | International Standard are encouraged to investigate the possibility of applying the most recent edition

of the Recommendations and Standards listed below. Members of IEC and ISO maintain registers of currently valid

International Standards. The Telecommunication Standardization Bureau of the ITU maintains a list of currently valid

ITU-T Recommendations.
2.1 Identical Recommendations | International Standards

– Recommendation ITU-T X.500 (2019) | ISO/IEC 9594-1:2020, Information technology – Open Systems

Interconnection – The Directory: Overview of concepts, models and services.

– Recommendation ITU-T X.501 (2019) | ISO/IEC 9594-2:2020, Information technology – Open Systems

Interconnection – The Directory: Models.

– Recommendation ITU-T X.509 (2019) | ISO/IEC 9594-8:2020, Information technology – Open Systems

Interconnection – The Directory: Public-key and attribute certificate frameworks.

– Recommendation ITU-T X.511 (2019) | ISO/IEC 9594-3:2020, Information technology – Open Systems

Interconnection – The Directory: Abstract service definition.

– Recommendation ITU-T X.518 (2019) | ISO/IEC 9594-4:2020, Information technology – Open Systems

Interconnection – The Directory: Procedures for distributed operation.

– Recommendation ITU-T X.519 (2019) | ISO/IEC 9594-5:2020, Information technology – Open Systems

Interconnection – The Directory: Protocol specifications.

– Recommendation ITU-T X.520 (2019) | ISO/IEC 9594-6:2020, Information technology – Open Systems

Interconnection – The Directory: Selected attribute types.

– Recommendation ITU-T X.521 (2019) | ISO/IEC 9594-7:2020, Information technology – Open Systems

Interconnection – The Directory: Selected object classes.

– Recommendation ITU-T X.680 (2015) | ISO/IEC 8824-1:2015, Information technology – Abstract Syntax

Notation One (ASN.1): Specification of basic notation.
3 Definitions

For the purposes of this Recommendation | International Standard, the following definitions apply.

3.1 Basic Directory definitions
The following term is defined in Rec. ITU-T X.500 | ISO/IEC 9594-1:
– (the) Directory.
© ISO/IEC 2020 – All rights reserved
Rec. ITU-T X.525 (10/2019) 1
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ISO/IEC 9594-9:2020 (E)
3.2 Directory model definitions
The following terms are defined in Rec. ITU-T X.501 | ISO/IEC 9594-2:
a) distinguished name;
b) Directory information tree (DIT);
c) DSA-specific entry (DSE);
d) DSA information model;
e) DSA information tree;
f) Directory system agent (DSA).
3.3 Abstract service definitions
The following term is defined in Rec. ITU-T X.511 | ISO/IEC 9594-3:
a) request;
b) requestor.
3.4 Distributed operation definitions
The following terms are defined in Rec. ITU-T X.518 | ISO/IEC 9594-4:
a) access point;
b) knowledge information;
c) name resolution;
d) naming context;
e) non-specific subordinate reference;
f) subordinate reference.
3.5 Protocol definitions
The following term is defined in Rec. ITU-T X.519 | ISO/IEC 9594-5:
a) application-association.
3.6 Replication definitions
The following terms are defined in this Recommendation | International Standard:

3.6.1 area prefix: The sequence of RDNs and associated administrative information common to all entries within a

replicated area.

3.6.2 attribute completeness: Indicates whether or not all user attributes are included in an entry-copy.

3.6.3 cache-copy: A copy of an entry (or part of an entry) whose consistency with its corresponding entry is

maintained by means outside the scope of this Directory Specification.

3.6.4 caching: The process of creating cache copies. This process is outside the scope of this Directory Specification.

3.6.5 consumer reference: The access point of the shadow consumer.
3.6.6 entry-copy: Shadowed information from an entry.

3.6.7 extended knowledge: Those subordinate and non-specific subordinate references that would be included as

subordinate knowledge if the replicated area were extended to the lower boundary of the naming context.

3.6.8 master DSA: The DSA which has administrative authority for a naming context. All adds, deletes and

modifications to entries in this naming context are done by the master DSA. The master DSA may enter into shadowing

agreements with other DSAs to provide copies of a subset of a naming context (see unit of replication).

3.6.9 primary shadowing: Shadowing where the shadow supplier is the master DSA.
3.6.10 replicated area: A subtree of the DIT for purposes of shadowing.
© ISO/IEC 2020 – All rights reserved
2 Rec. ITU-T X.525 (10/2019)
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ISO/IEC 9594-9:2020 (E)

3.6.11 replication: The process by which copies of entry and operational information are held by DSAs other than the

master DSA.

3.6.12 replication base entry: The distinguished name of the root vertex of a replicated area.

3.6.13 secondary shadowing: Shadowing where the shadow supplier is not the master DSA.

3.6.14 shadow consumer: A DSA that receives shadowed information.

3.6.15 shadow operational binding: The relationship between two DSAs, one acting as a supplier of replicated

information and the other as its consumer.

3.6.16 shadow service: The service provided to perform shadowing between two DSAs that have entered into one or

more shadowing agreements.

3.6.17 shadow supplier: A DSA that provides shadowed information. This DSA may or may not be the master DSA.

3.6.18 shadowed DSA specific entry (SDSE): A unit of shadowed information which is associated with a specific

name; it represents the information taken from a DSE which is shadowed.

3.6.19 shadowed information: The complete set of information associated with a unit of replication. Shadowed

information is conceptually held both by the shadow supplier and the shadow consumer for the purposes of the shadow

protocol and comprises a tree shaped structure of shadowed DSEs.

3.6.20 shadowing: Replication between two DSAs whereby shadowed information is copied and maintained using the

Directory Information Shadowing Protocol.

3.6.21 shadowing agreement: The terms specific to a particular agreement required for shadowing to occur between

a pair of DSAs.

3.6.22 subordinate completeness: Indicates whether or not subordinate knowledge is complete for an entry-copy.

3.6.23 supplier reference: The access point of the shadow supplier.

3.6.24 unit of replication: A specification of the information to be shadowed, including (optionally) subordinate

knowledge information.
4 Abbreviations

For the purposes of this Recommendation | International Standard, the following abbreviations apply:

ACI Access Control Information
DIB Directory Information Base
DISP Directory Information Shadowing Protocol
DIT Directory Information Tree
DMD Directory Management Domain
DSA Directory System Agent
DSE DSA-Specific Entry
DUA Directory User Agent
LDAP Lightweight Directory Access Protocol
RDN Relative Distinguished Name
SDSE Shadowed DSA-Specific Entry
TCP/IP Transmission Control Protocol/Internet Protocol
5 Conventions

The term "Directory Specification" (as in "this Directory Specification") shall be taken to mean Rec. ITU-T X.525 |

ISO/IEC 9594-9. The term "Directory Specifications" shall be taken to mean the Rec. ITU-T X.500 | ISO/IEC 9594-1,

Rec. ITU-T X.501 | ISO/IEC 9594-2, Rec. ITU-T X.511 | ISO/IEC 9594-3, Rec. ITU-T X.518 | ISO/IEC 9594-4,

Rec. ITU-T X.519 | ISO/IEC 9594-5, Rec. ITU-T X.520 | ISO/IEC 9594-6, Rec. ITU-T X.521 | ISO/IEC 9594-7 and Rec.

ITU-T X.525 | ISO/IEC 9594-9.
© ISO/IEC 2020 – All rights reserved
Rec. ITU-T X.525 (10/2019) 3
---------------------- Page: 8 ----------------------
ISO/IEC 9594-9:2020 (E)

If an International Standard or ITU-T Recommendation is referenced within normal text without an indication of the

edition, the edition shall be taken to be the latest one as specified in the normative references clause.

Prior to year 2020, the parts making up the Directory Specifications have been progressed together and can therefore

collectively be identified as the Directory Specifications of a specific edition using the format: Rec. ITU-T X.5** (yyyy)

| ISO/IEC 9594-*:yyyy (e.g.; Rec ITU-T X.5** (1993) | ISO/IEC 9594-*:1995).

This Directory Specification makes extensive use of the Abstract Syntax Notation One (ASN.1) for the formal

specification of data types and values, as it is specified in Rec. ITU-T X.680 | ISO/IEC 8824-1, Rec. ITU-T X.681 (2015)

| ISO/IEC 8824-2, Rec. ITU-T X.682 (2015) | ISO/IEC 8824-3, Rec. ITU-T X.683 (2015) | ISO/IEC 8824-4 and Rec. ITU-

T X.690 | ISO/IEC 8825-1.

This Directory Specification presents ASN.1 notation in the bold Courier New typeface. When ASN.1 types and values

are referenced in normal text, they are differentiated from normal text by presenting them in the bold Courier New

typeface. The names of procedures, typically referenced when specifying the semantics of processing, are differentiated

from normal text by displaying them in bold Times New Roman. Access control permissions are presented in italicized

Times New Roman.

If the items in a list are numbered (as opposed to using "–" or letters), then the items shall be considered steps in a

procedure.
6 Replication in the Directory

Replicated (copied) information can exist in the Directory. Shadowing is the mechanism for replication defined in this

Directory Specification. Directory information can also be replicated by means outside this Directory Specification, such

as caching. Any such alternative means of replication will need to ensure that exactly one instance of each replicated entry

is identified as the master copy if the Directory and DSA abstract services are to be used.

Service controls provide the ability to control whether replicated information may be used in support of Directory

operations, regardless of the replication mechanism used to acquire the copy. DISP is protected by the underlying protocol

as defined in Rec. ITU-T X.519 | ISO/IEC 9594-5.
6.1 Caching

One method of replicating Directory information is caching. Caching procedures are considered to be almost entirely

governed by local policies, and therefore outside the scope of this Directory Specification.

6.2 Shadowing

Another method of replicating Directory information is shadowing. An overview of the Directory information shadow

service is found in clause 7. Before shadowing can occur, an agreement, covering the conditions under which shadowing

may occur is required. Although such agreements may be established in a variety of ways, such as policy statements

covering all DSAs within a given Directory management domain (DMD), the shadowing is always between a pair of

DSA. The technical parameters for the subsequent shadowing are specified as part of the resulting shadowing agreement.

Components of the shadowing agreement are defined in clause 9.

Once the terms of the agreement have been established, the DSAs may initiate, modify and subsequently terminate the

shadowing agreement. This may be done through a shadow operational binding as defined in clause 8.

This shadowing service for the Directory is based on the models established in Rec. ITU-T X.501 | ISO/IEC 9594-2, to

satisfy the requirements outlined in Rec. ITU-T X.500 | ISO/IEC 9594-1. The protocol specification for shadowing and

conformance requirements are provided in Rec. ITU-T X.519 | ISO/IEC 9594-5. In addition, this Directory Specification

provides the definition of an operational binding for the purpose of initiating, modifying, and terminating shadowing

agreements between DSAs. This operational binding type is defined using the tools specified in Rec. ITU-T X.501 |

ISO/IEC 9594-2.

The Directory information shadow service is defined in clause 10. The actual shadowing occurs through the set of

operations defined in clause 11. These operations accommodate the transfer of Directory information and updates to the

shadowed information.

The use of shadowed information by a DSA to satisfy a Directory request is described in Rec. ITU-T X.518 |

ISO/IEC 9594-4.
© ISO/IEC 2020 – All rights reserved
4 Rec. ITU-T X.525 (10/2019)
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ISO/IEC 9594-9:2020 (E)
6.3 Shadowing functional model

In the standardized form of Directory replication, termed shadowing, a DSA may assume the role of shadow supplier, the

source of shadowed information, or shadow consumer, the recipient of shadowed information. The role played by a DSA

when engaging in standardized replication activities (shadow supplier or shadow consumer) is always with respect to

another DSA which plays the reciprocal role (shadow consumer or shadow supplier).

A given DSA may assume both roles, either:

– with respect to different DSAs for the same or different units of replication; or

– with respect to a single DSA (which plays the reciprocal role) for different units of replication.

The shadowing functional model addresses two approaches to shadowing Directory information:

– a primary shadowing policy requires that each shadow consumer receives its updates directly from the

master DSA for the unit of replication;

– a secondary shadowing policy permits a shadow consumer to assume the shadow supplier role with respect

to shadow consumers not having a shadowing agreement directly with the master DSA.

The characteristics of these two policies and their approach to addressing performance, availability, reliability and

recovery are described below.
6.3.1 Primary shadowing

Figure 1 depicts primary shadowing. In this case, the shadowing policy in effect has the following characteristics:

a) the master DSA is the only shadow supplier for a replicated area;
b) each shadow consumer has a direct shadowing agreement with the master DSA;

c) only read, compare, search, and list operations may be performed at a shadow consumer holding shadowed

information. All modification operations are directed to the master DSA.

Because it allows for the placement of copies of often requested information, or knowledge of it, closer to the requestor,

this approach may be used to satisfy the performance requirement. Also, because this approach provides for the

redundancy of individual entry or knowledge information, it is possible, in a primitive sense, to provide for availability,

reliability, and recovery.
Shadow
DUA or
Master
consumer
LDAP
DSA
DSA
client
Shadow Shadow
DUA or
consumer consumer
LDAP
DUA or
DSA DSA
client
LDAP
client
Shadow updates
X.525(12)_F01
Figure 1 – Primary shadowing
6.3.2 Secondary shadowing

Figure 2 depicts secondary shadowing. In this case, the shadowing policy in effect has the following characteristics:

a) The master DSA is not the only shadow supplier for a replicated area. Only some shadow consumers have

a direct shadowing agreement with the master DSA as their shadow supplier.

b) Other shadow consumers may have a shadowing agreement with a shadow supplier that is not the master

for the unit of replication. The shadowing agreements between the master DSA and its direct shadow

consumers may, however, have an impact on secondary shadowing agreements.

c) Only read, compare, search, and list operations may be performed at a shadow consumer holding shadowed

information. All modification operations are directed to the master DSA, either directly (if a secondary

shadow consumer DSA has knowledge of the master DSA) or indirectly via the shadow supplier DSA(s).

© ISO/IEC 2020 – All rights reserved
Rec. ITU-T X.525 (10/2019) 5
---------------------- Page: 10 ----------------------
ISO/IEC 9594-9:2020 (E)

Secondary shadowing is very similar to primary shadowing in the way that it provides for performance, availability,

reliability and recovery. It differs in that it relieves the single master DSA of the burden of directly supplying all shadow

consumers with the shadowed information. This is a desirable combination in environments where a large number of

shadow consumers are holding the same shadowed information.
DUA or
Master
LDAP
DSA
client
Shadow
consumer Shadow
DUA or
and shadow
consumer
LDAP
DSA
supplier
client
DSA
DUA or
LDAP
Shadow updates
client
X.525(12)_F02
Figure 2 – Secondary shadowing
7 Shadowing in the Directory

The Directory information shadow service defined here provides the Directory with a standardized mechanism to provide

and support shadowed information. In outline, the shadow supplier maintains, for each shadowing agreement, information

which is to be shadowed (the shadowed information). This information i
...

INTERNATIONAL ISO/IEC
STANDARD 9594-9
Eighth edition
2020-11
Information technology — Open
systems interconnection —
Part 9:
The Directory: Replication
Reference number
ISO/IEC 9594-9:2020(E)
ISO/IEC 2020
---------------------- Page: 1 ----------------------
ISO/IEC 9594-9:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO/IEC 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/IEC 9594-9:2020(E)
Foreword

ISO (the International Organization for Standardization) and IEC (the International Electrotechnical

Commission) form the specialized system for worldwide standardization. National bodies that are

members of ISO or IEC participate in the development of International Standards through technical

committees established by the respective organization to deal with particular fields of technical activity.

ISO and IEC technical committees collaborate in fields of mutual interest. Other international

organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the

work.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of document should be noted (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights. Details

of any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents) or the IEC list of patent

declarations received (see http://patents.iec.ch).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the World

Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT),
see www.iso.org/iso/foreword.html.

This document was prepared by ITU-T as ITU-T X.525 (10/2019) and drafted in accordance with

its editorial rules, in collaboration with Joint Technical Committee ISO/IEC JTC 1, Information

technology, Subcommittee SC 6, Telecommunications and information exchange between systems.

This eighth edition cancels and replaces the seventh edition (ISO/IEC 9594-9:2017), which has been

technically revised.
A list of all parts in the ISO/IEC 9594 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body.

A complete listing of these bodies can be found at www.iso.org/members.html.
© ISO/IEC 2020 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/IEC 9594-9:2020 (E)
CONTENTS
Page

1 Scope .............................................................................................................................................................. 1

2 Normative references...................................................................................................................................... 1

2.1 Identical Recommendations | International Standards ........................................................................ 1

3 Definitions ...................................................................................................................................................... 1

3.1 Basic Directory definitions .................................................................................................................. 1

3.2 Directory model definitions ................................................................................................................ 2

3.3 Abstract service definitions ................................................................................................................. 2

3.4 Distributed operation definitions ......................................................................................................... 2

3.5 Protocol definitions ............................................................................................................................. 2

3.6 Replication definitions ........................................................................................................................ 2

4 Abbreviations ................................................................................................................................................. 3

5 Conventions .................................................................................................................................................... 3

6 Replication in the Directory ........................................................................................................................... 4

6.1 Caching ............................................................................................................................................... 4

6.2 Shadowing ........................................................................................................................................... 4

6.3 Shadowing functional model ............................................................................................................... 5

7 Shadowing in the Directory ............................................................................................................................ 6

7.1 Shadowing agreement ......................................................................................................................... 6

7.2 Shadowed information ........................................................................................................................ 7

7.3 Shadow operations .............................................................................................................................. 10

7.4 DSA Shadow Bind and DSA Shadow Unbind operation .................................................................... 11

8 Shadow operational binding ........................................................................................................................... 11

8.1 Shadow operational binding type characteristics ................................................................................ 11

8.2 DSA procedures for operational binding management ....................................................................... 12

8.3 Operational binding ............................................................................................................................. 13

9 Shadowing agreement .................................................................................................................................... 14

9.1 Shadowing agreement specification .................................................................................................... 14

9.2 Unit of replication ............................................................................................................................... 15

9.3 Update mode ....................................................................................................................................... 20

10 Directory information shadow service............................................................................................................ 21

10.1 Shadow supplier initiated service ........................................................................................................ 21

10.2 Shadow consumer initiated service ..................................................................................................... 22

11 Shadow operations ......................................................................................................................................... 22

11.1 Coordinate Shadow Update operation ................................................................................................. 22

11.2 Request Shadow Update operation ...................................................................................................... 24

11.3 Update Shadow operation ................................................................................................................... 26

12 Shadow error .................................................................................................................................................. 30

12.1 Shadow error problems ....................................................................................................................... 30

12.2 Last update .......................................................................................................................................... 31

12.3 Update window ................................................................................................................................... 31

12.4 Common results .................................................................................................................................. 31

Annex A – Directory shadow abstract service in ASN.1 ........................................................................................... 32

Annex B – Amendments and corrigenda ................................................................................................................... 38

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ISO/IEC 9594-9:2020 (E)
Introduction

This Recommendation | International Standard, together with other Recommendations | International Standards, has been

produced to facilitate the interconnection of information processing systems to provide Directory services. A set of such

systems, together with the Directory information that they hold, can be viewed as an integrated whole, called the

Directory. The information held by the Directory, collectively known as the Directory Information Base (DIB) is typically

used to facilitate communication between, with or about objects such as application-entities, people, terminals and

distribution lists.

The Directory plays a significant role in Open Systems Interconnection, whose aim is to allow, with a minimum of

technical agreement outside of the interconnection standards themselves, the interconnection of information processing

systems:
– from different manufacturers;
– under different managements;
– of different levels of complexity; and
– of different ages.

This Recommendation | International Standard defines the replication capabilities provided by Directory system agents

(DSAs) to improve the level of service to Directory users.

This Recommendation | International Standard provides the foundation frameworks upon which industry profiles can be

defined by other standards groups and industry forums. Many of the features defined as optional in these frameworks may

be mandated for use in certain environments through profiles. This ninth edition technically revises and enhances the

eighth edition of this Recommendation | International Standard.

Annex A, which is an integral part of this Recommendation | International Standard, provides the ASN.1 module for the

Directory shadow abstract service.

Annex B, which is not an integral part of this Recommendation | International Standard, lists the amendments and defect

reports that have been incorporated to form this edition of this Recommendation | International Standard.

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ISO/IEC 9594-9:2020 (E)
INTERNATIONAL STANDARD
ITU-T RECOMMENDATION

Information technology – Open Systems Interconnection – The Directory: Replication

1 Scope

This Recommendation | International Standard specifies a shadow service which Directory system agents (DSAs) may

use to replicate Directory information. The service allows Directory information to be replicated among DSAs to improve

service to Directory users. The shadowed information is updated, using the defined protocol, thereby improving the

service provided to users of the Directory.
2 Normative references

The following Recommendations and International Standards contain provisions which, through reference in this text,

constitute provisions of this Recommendation | International Standard. At the time of publication, the editions indicated

were valid. All Recommendations and Standards are subject to revision, and parties to agreements based on this

Recommendation | International Standard are encouraged to investigate the possibility of applying the most recent edition

of the Recommendations and Standards listed below. Members of IEC and ISO maintain registers of currently valid

International Standards. The Telecommunication Standardization Bureau of the ITU maintains a list of currently valid

ITU-T Recommendations.
2.1 Identical Recommendations | International Standards

– Recommendation ITU-T X.500 (2019) | ISO/IEC 9594-1:2020, Information technology – Open Systems

Interconnection – The Directory: Overview of concepts, models and services.

– Recommendation ITU-T X.501 (2019) | ISO/IEC 9594-2:2020, Information technology – Open Systems

Interconnection – The Directory: Models.

– Recommendation ITU-T X.509 (2019) | ISO/IEC 9594-8:2020, Information technology – Open Systems

Interconnection – The Directory: Public-key and attribute certificate frameworks.

– Recommendation ITU-T X.511 (2019) | ISO/IEC 9594-3:2020, Information technology – Open Systems

Interconnection – The Directory: Abstract service definition.

– Recommendation ITU-T X.518 (2019) | ISO/IEC 9594-4:2020, Information technology – Open Systems

Interconnection – The Directory: Procedures for distributed operation.

– Recommendation ITU-T X.519 (2019) | ISO/IEC 9594-5:2020, Information technology – Open Systems

Interconnection – The Directory: Protocol specifications.

– Recommendation ITU-T X.520 (2019) | ISO/IEC 9594-6:2020, Information technology – Open Systems

Interconnection – The Directory: Selected attribute types.

– Recommendation ITU-T X.521 (2019) | ISO/IEC 9594-7:2020, Information technology – Open Systems

Interconnection – The Directory: Selected object classes.

– Recommendation ITU-T X.680 (2015) | ISO/IEC 8824-1:2015, Information technology – Abstract Syntax

Notation One (ASN.1): Specification of basic notation.
3 Definitions

For the purposes of this Recommendation | International Standard, the following definitions apply.

3.1 Basic Directory definitions
The following term is defined in Rec. ITU-T X.500 | ISO/IEC 9594-1:
– (the) Directory.
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ISO/IEC 9594-9:2020 (E)
3.2 Directory model definitions
The following terms are defined in Rec. ITU-T X.501 | ISO/IEC 9594-2:
a) distinguished name;
b) Directory information tree (DIT);
c) DSA-specific entry (DSE);
d) DSA information model;
e) DSA information tree;
f) Directory system agent (DSA).
3.3 Abstract service definitions
The following term is defined in Rec. ITU-T X.511 | ISO/IEC 9594-3:
a) request;
b) requestor.
3.4 Distributed operation definitions
The following terms are defined in Rec. ITU-T X.518 | ISO/IEC 9594-4:
a) access point;
b) knowledge information;
c) name resolution;
d) naming context;
e) non-specific subordinate reference;
f) subordinate reference.
3.5 Protocol definitions
The following term is defined in Rec. ITU-T X.519 | ISO/IEC 9594-5:
a) application-association.
3.6 Replication definitions
The following terms are defined in this Recommendation | International Standard:

3.6.1 area prefix: The sequence of RDNs and associated administrative information common to all entries within a

replicated area.

3.6.2 attribute completeness: Indicates whether or not all user attributes are included in an entry-copy.

3.6.3 cache-copy: A copy of an entry (or part of an entry) whose consistency with its corresponding entry is

maintained by means outside the scope of this Directory Specification.

3.6.4 caching: The process of creating cache copies. This process is outside the scope of this Directory Specification.

3.6.5 consumer reference: The access point of the shadow consumer.
3.6.6 entry-copy: Shadowed information from an entry.

3.6.7 extended knowledge: Those subordinate and non-specific subordinate references that would be included as

subordinate knowledge if the replicated area were extended to the lower boundary of the naming context.

3.6.8 master DSA: The DSA which has administrative authority for a naming context. All adds, deletes and

modifications to entries in this naming context are done by the master DSA. The master DSA may enter into shadowing

agreements with other DSAs to provide copies of a subset of a naming context (see unit of replication).

3.6.9 primary shadowing: Shadowing where the shadow supplier is the master DSA.
3.6.10 replicated area: A subtree of the DIT for purposes of shadowing.
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ISO/IEC 9594-9:2020 (E)

3.6.11 replication: The process by which copies of entry and operational information are held by DSAs other than the

master DSA.

3.6.12 replication base entry: The distinguished name of the root vertex of a replicated area.

3.6.13 secondary shadowing: Shadowing where the shadow supplier is not the master DSA.

3.6.14 shadow consumer: A DSA that receives shadowed information.

3.6.15 shadow operational binding: The relationship between two DSAs, one acting as a supplier of replicated

information and the other as its consumer.

3.6.16 shadow service: The service provided to perform shadowing between two DSAs that have entered into one or

more shadowing agreements.

3.6.17 shadow supplier: A DSA that provides shadowed information. This DSA may or may not be the master DSA.

3.6.18 shadowed DSA specific entry (SDSE): A unit of shadowed information which is associated with a specific

name; it represents the information taken from a DSE which is shadowed.

3.6.19 shadowed information: The complete set of information associated with a unit of replication. Shadowed

information is conceptually held both by the shadow supplier and the shadow consumer for the purposes of the shadow

protocol and comprises a tree shaped structure of shadowed DSEs.

3.6.20 shadowing: Replication between two DSAs whereby shadowed information is copied and maintained using the

Directory Information Shadowing Protocol.

3.6.21 shadowing agreement: The terms specific to a particular agreement required for shadowing to occur between

a pair of DSAs.

3.6.22 subordinate completeness: Indicates whether or not subordinate knowledge is complete for an entry-copy.

3.6.23 supplier reference: The access point of the shadow supplier.

3.6.24 unit of replication: A specification of the information to be shadowed, including (optionally) subordinate

knowledge information.
4 Abbreviations

For the purposes of this Recommendation | International Standard, the following abbreviations apply:

ACI Access Control Information
DIB Directory Information Base
DISP Directory Information Shadowing Protocol
DIT Directory Information Tree
DMD Directory Management Domain
DSA Directory System Agent
DSE DSA-Specific Entry
DUA Directory User Agent
LDAP Lightweight Directory Access Protocol
RDN Relative Distinguished Name
SDSE Shadowed DSA-Specific Entry
TCP/IP Transmission Control Protocol/Internet Protocol
5 Conventions

The term "Directory Specification" (as in "this Directory Specification") shall be taken to mean Rec. ITU-T X.525 |

ISO/IEC 9594-9. The term "Directory Specifications" shall be taken to mean the Rec. ITU-T X.500 | ISO/IEC 9594-1,

Rec. ITU-T X.501 | ISO/IEC 9594-2, Rec. ITU-T X.511 | ISO/IEC 9594-3, Rec. ITU-T X.518 | ISO/IEC 9594-4,

Rec. ITU-T X.519 | ISO/IEC 9594-5, Rec. ITU-T X.520 | ISO/IEC 9594-6, Rec. ITU-T X.521 | ISO/IEC 9594-7 and Rec.

ITU-T X.525 | ISO/IEC 9594-9.
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ISO/IEC 9594-9:2020 (E)

If an International Standard or ITU-T Recommendation is referenced within normal text without an indication of the

edition, the edition shall be taken to be the latest one as specified in the normative references clause.

Prior to year 2020, the parts making up the Directory Specifications have been progressed together and can therefore

collectively be identified as the Directory Specifications of a specific edition using the format: Rec. ITU-T X.5** (yyyy)

| ISO/IEC 9594-*:yyyy (e.g.; Rec ITU-T X.5** (1993) | ISO/IEC 9594-*:1995).

This Directory Specification makes extensive use of the Abstract Syntax Notation One (ASN.1) for the formal

specification of data types and values, as it is specified in Rec. ITU-T X.680 | ISO/IEC 8824-1, Rec. ITU-T X.681 (2015)

| ISO/IEC 8824-2, Rec. ITU-T X.682 (2015) | ISO/IEC 8824-3, Rec. ITU-T X.683 (2015) | ISO/IEC 8824-4 and Rec. ITU-

T X.690 | ISO/IEC 8825-1.

This Directory Specification presents ASN.1 notation in the bold Courier New typeface. When ASN.1 types and values

are referenced in normal text, they are differentiated from normal text by presenting them in the bold Courier New

typeface. The names of procedures, typically referenced when specifying the semantics of processing, are differentiated

from normal text by displaying them in bold Times New Roman. Access control permissions are presented in italicized

Times New Roman.

If the items in a list are numbered (as opposed to using "–" or letters), then the items shall be considered steps in a

procedure.
6 Replication in the Directory

Replicated (copied) information can exist in the Directory. Shadowing is the mechanism for replication defined in this

Directory Specification. Directory information can also be replicated by means outside this Directory Specification, such

as caching. Any such alternative means of replication will need to ensure that exactly one instance of each replicated entry

is identified as the master copy if the Directory and DSA abstract services are to be used.

Service controls provide the ability to control whether replicated information may be used in support of Directory

operations, regardless of the replication mechanism used to acquire the copy. DISP is protected by the underlying protocol

as defined in Rec. ITU-T X.519 | ISO/IEC 9594-5.
6.1 Caching

One method of replicating Directory information is caching. Caching procedures are considered to be almost entirely

governed by local policies, and therefore outside the scope of this Directory Specification.

6.2 Shadowing

Another method of replicating Directory information is shadowing. An overview of the Directory information shadow

service is found in clause 7. Before shadowing can occur, an agreement, covering the conditions under which shadowing

may occur is required. Although such agreements may be established in a variety of ways, such as policy statements

covering all DSAs within a given Directory management domain (DMD), the shadowing is always between a pair of

DSA. The technical parameters for the subsequent shadowing are specified as part of the resulting shadowing agreement.

Components of the shadowing agreement are defined in clause 9.

Once the terms of the agreement have been established, the DSAs may initiate, modify and subsequently terminate the

shadowing agreement. This may be done through a shadow operational binding as defined in clause 8.

This shadowing service for the Directory is based on the models established in Rec. ITU-T X.501 | ISO/IEC 9594-2, to

satisfy the requirements outlined in Rec. ITU-T X.500 | ISO/IEC 9594-1. The protocol specification for shadowing and

conformance requirements are provided in Rec. ITU-T X.519 | ISO/IEC 9594-5. In addition, this Directory Specification

provides the definition of an operational binding for the purpose of initiating, modifying, and terminating shadowing

agreements between DSAs. This operational binding type is defined using the tools specified in Rec. ITU-T X.501 |

ISO/IEC 9594-2.

The Directory information shadow service is defined in clause 10. The actual shadowing occurs through the set of

operations defined in clause 11. These operations accommodate the transfer of Directory information and updates to the

shadowed information.

The use of shadowed information by a DSA to satisfy a Directory request is described in Rec. ITU-T X.518 |

ISO/IEC 9594-4.
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6.3 Shadowing functional model

In the standardized form of Directory replication, termed shadowing, a DSA may assume the role of shadow supplier, the

source of shadowed information, or shadow consumer, the recipient of shadowed information. The role played by a DSA

when engaging in standardized replication activities (shadow supplier or shadow consumer) is always with respect to

another DSA which plays the reciprocal role (shadow consumer or shadow supplier).

A given DSA may assume both roles, either:

– with respect to different DSAs for the same or different units of replication; or

– with respect to a single DSA (which plays the reciprocal role) for different units of replication.

The shadowing functional model addresses two approaches to shadowing Directory information:

– a primary shadowing policy requires that each shadow consumer receives its updates directly from the

master DSA for the unit of replication;

– a secondary shadowing policy permits a shadow consumer to assume the shadow supplier role with respect

to shadow consumers not having a shadowing agreement directly with the master DSA.

The characteristics of these two policies and their approach to addressing performance, availability, reliability and

recovery are described below.
6.3.1 Primary shadowing

Figure 1 depicts primary shadowing. In this case, the shadowing policy in effect has the following characteristics:

a) the master DSA is the only shadow supplier for a replicated area;
b) each shadow consumer has a direct shadowing agreement with the master DSA;

c) only read, compare, search, and list operations may be performed at a shadow consumer holding shadowed

information. All modification operations are directed to the master DSA.

Because it allows for the placement of copies of often requested information, or knowledge of it, closer to the requestor,

this approach may be used to satisfy the performance requirement. Also, because this approach provides for the

redundancy of individual entry or knowledge information, it is possible, in a primitive sense, to provide for availability,

reliability, and recovery.
Shadow
DUA or
Master
consumer
LDAP
DSA
DSA
client
Shadow Shadow
DUA or
consumer consumer
LDAP
DUA or
DSA DSA
client
LDAP
client
Shadow updates
X.525(12)_F01
Figure 1 – Primary shadowing
6.3.2 Secondary shadowing

Figure 2 depicts secondary shadowing. In this case, the shadowing policy in effect has the following characteristics:

a) The master DSA is not the only shadow supplier for a replicated area. Only some shadow consumers have

a direct shadowing agreement with the master DSA as their shadow supplier.

b) Other shadow consumers may have a shadowing agreement with a shadow supplier that is not the master

for the unit of replication. The shadowing agreements between the master DSA and its direct shadow

consumers may, however, have an impact on secondary shadowing agreements.

c) Only read, compare, search, and list operations may be performed at a shadow consumer holding shadowed

information. All modification operations are directed to the master DSA, either directly (if a secondary

shadow consumer DSA has knowledge of the master DSA) or indirectly via the shadow supplier DSA(s).

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ISO/IEC 9594-9:2020 (E)

Secondary shadowing is very similar to primary shadowing in the way that it provides for performance, availability,

reliability and recovery. It differs in that it relieves the single master DSA of the burden of directly supplying all shadow

consumers with the shadowed information. This is a desirable combination in environments where a large number of

shadow consumers are holding the same shadowed information.
DUA or
Master
LDAP
DSA
client
Shadow
consumer Shadow
DUA or
and shadow
consumer
LDAP
DSA
supplier
client
DSA
DUA or
LDAP
Shadow updates
client
X.525(12)_F02
Figure 2 – Secondary shadowing
7 Shadowing in the Directory

The Directory information shadow service defined here provides the Directory with a standardized mechanism to provide

and support shadowed information. In outline, the shadow supplier maintains, for each shad

...

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