ISO/IEC 9594-9:2014

Information technology - Open Systems Interconnection - The Directory - Part 9: Replication

ISO/IEC 9594 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. ISO/IEC 9594-9:2014 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, and provides for the automatic updating of this information.

Technologies de l'information — Interconnexion de systèmes ouverts (OSI) — L'annuaire — Partie 9: Duplication

General Information

• Status: Withdrawn
• Publication Date: 24-Feb-2014
• Withdrawal Date: 24-Feb-2014
• ICS: 35.100.70 - Application layer
• Technical Committee: ISO/IEC JTC 1/SC 6 - Telecommunications and information exchange between systems
• Drafting Committee: ISO/IEC JTC 1/SC 6 - Telecommunications and information exchange between systems
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 05-May-2017
• Completion Date: 30-Oct-2025

Relations

• Revised: ISO/IEC 9594-9:2017 - Information technology - Open Systems Interconnection - The Directory - Part 9: Replication
• Effective Date: 10-Dec-2016
• Revises: ISO/IEC 9594-9:2008 - Information technology - Open Systems Interconnection - The Directory: Replication - Part 9:
• Effective Date: 31-Aug-2013

Standards Content (Sample)

INTERNATIONAL ISO/IEC
STANDARD 9594-9
Sixth edition
2014-03-01
Information technology — Open Systems
Interconnection — The Directory —
Part 9:
Replication
Technologies de l'information — Interconnexion de systèmes ouverts
(OSI) — L'annuaire
Partie 9: Duplication
Reference number
©
ISO/IEC 2014
©  ISO/IEC 2014
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ii © ISO/IEC 2014 – All rights reserved

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. In the field of information
technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of the joint technical committee is to prepare International Standards. Draft International
Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as
an International Standard requires approval by at least 75 % of the national bodies casting a vote.
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.
ISO/IEC 9594-9 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 6, Telecommunications and information exchange between systems, in collaboration with
ITU-T. The identical text is published as Rec. ITU-T X.525 (10/2012).
This sixth edition cancels and replaces the fifth edition (ISO/IEC 9594-9:2008), which has been
technically revised. It also incorporates the Technical Corrigendum ISO/IEC 9594-9:2008/Cor.1:2011.
ISO/IEC 9594 consists of the following parts, under the general title Information technology — Open Systems
Interconnection — The Directory:
— Part 1: Overview of concepts, models and services
— Part 2: Models
— Part 3: Abstract service definition
— Part 4: Procedures for distributed operation
— Part 5: Protocol specifications
— Part 6: Selected attribute types
— Part 7: Selected object classes
— Part 8: Public-key and attribute certificate frameworks
— Part 9: Replication
© ISO/IEC 2014 – All rights reserved

CONTENTS
Page
1 Scope . 1
2 Normative references . 1
2.1 Identical Recommendations | International Standards . 1
3 Definitions . 2
3.1 Basic Directory definitions . 2
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 . 4
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 . 7
7.2 Shadowed information . 7
7.3 Shadow operations . 11
7.4 DSA Shadow Bind and DSA Shadow Unbind operation . 12
8 Shadow operational binding . 12
8.1 Shadow operational binding type characteristics . 12
8.2 DSA procedures for operational binding management . 13
8.3 Operational binding . 14
9 Shadowing agreement . 15
9.1 Shadowing agreement specification . 15
9.2 Unit of replication . 16
9.3 Update mode . 21
10 Directory information shadow service . 22
10.1 Shadow supplier initiated service . 22
10.2 Shadow consumer initiated service . 23
11 Shadow operations . 23
11.1 Coordinate Shadow Update operation . 23
11.2 Request Shadow Update operation . 25
11.3 Update Shadow operation . 27
12 Shadow error . 30
12.1 Shadow error problems . 31
12.2 Last update . 31
12.3 Update window . 31
12.4 Common results . 32
Annex A – Directory shadow abstract service in ASN.1 . 33
Annex B – Amendments and corrigenda . 39

Rec. ITU-T X.525 (10/2012) iii

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 seventh edition technically revises and
enhances the sixth edition of this Recommendation | International Standard.
This seventh edition specifies versions 1 and 2 of the Directory protocols.
The first and second editions specified only version 1. Most of the services and protocols specified in this edition are
designed to function under version 1. However, some enhanced services and protocols, e.g., signed errors, will not
function unless all Directory entities involved in the operation have negotiated version 2. Whichever version has been
negotiated, differences between the services and between the protocols defined in the six editions, except for those
specifically assigned to version 2, are accommodated using the rules of extensibility defined in Rec. ITU-T X.519 |
ISO/IEC 9594-5.
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.
iv Rec. ITU-T X.525 (10/2012)
INTERNATIONAL STANDARD
RECOMMENDATION ITU-T
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.200 (1994) | ISO/IEC 7498-1:1994, Information technology – Open Systems
Interconnection – Basic Reference Model: The Basic Model.
– Recommendation ITU-T X.500 (2012) | ISO/IEC 9594-1:2014, Information technology – Open Systems
Interconnection – The Directory: Overview of concepts, models and services.
– Recommendation ITU-T X.501 (2012) | ISO/IEC 9594-2:2014, Information technology – Open Systems
Interconnection – The Directory: Models.
– Recommendation ITU-T X.509 (2012) | ISO/IEC 9594-8:2014, Information technology – Open Systems
Interconnection – The Directory: Public-key and attribute certificate frameworks.
– Recommendation ITU-T X.511 (2012) | ISO/IEC 9594-3:2014, Information technology – Open Systems
Interconnection – The Directory: Abstract service definition.
– Recommendation ITU-T X.518 (2012) | ISO/IEC 9594-4:2014, Information technology – Open Systems
Interconnection – The Directory: Procedures for distributed operation.
– Recommendation ITU-T X.519 (2012) | ISO/IEC 9594-5:2014, Information technology – Open Systems
Interconnection – The Directory: Protocol specifications.
– Recommendation ITU-T X.520 (2012) | ISO/IEC 9594-6:2014, Information technology – Open Systems
Interconnection – The Directory: Selected attribute types.
– Recommendation ITU-T X.521 (2012) | ISO/IEC 9594-7:2014, Information technology – Open Systems
Interconnection – The Directory: Selected object classes.
– Recommendation ITU-T X.680 (2008) | ISO/IEC 8824-1:2008, Information technology – Abstract
Syntax Notation One (ASN.1): Specification of basic notation.
– Recommendation ITU-T X.681 (2008) | ISO/IEC 8824-2:2008, Information technology – Abstract
Syntax Notation One (ASN.1): Information object specification.
– Recommendation ITU-T X.682 (2008) | ISO/IEC 8824-3:2008, Information technology – Abstract
Syntax Notation One (ASN.1): Constraint specification.
– Recommendation ITU-T X.683 (2008) | ISO/IEC 8824-4:2008, Information technology – Abstract
Syntax Notation One (ASN.1): Parameterization of ASN.1 specifications.
Rec. ITU-T X.525 (10/2012) 1
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.
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.
2 Rec. ITU-T X.525 (10/2012)
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.
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
Rec. ITU-T X.525 (10/2012) 3
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 X.500-series Recommendations and all
parts of ISO/IEC 9594.
This Directory Specification uses the term first edition systems to refer to systems conforming to the first edition of the
Directory Specifications, i.e., the 1988 edition of the CCITT X.500-series Recommendations and the
ISO/IEC 9594:1990 edition.
This Directory Specification uses the term second edition systems to refer to systems conforming to the second edition
of the Directory Specifications, i.e., the 1993 edition of the ITU-T X.500-series Recommendations and the
ISO/IEC 9594:1995 edition.
This Directory Specification uses the term third edition systems to refer to systems conforming to the third edition of the
Directory Specifications, i.e., the 1997 edition of the ITU-T X.500-series Recommendations and the
ISO/IEC 9594:1998 edition.
This Directory Specification uses the term fourth edition systems to refer to systems conforming to the fourth edition of
the Directory Specifications, i.e., the 2001 editions of Recs ITU-T X.500, ITU-T X.501, ITU-T X.511, ITU-T X.518,
ITU-T X.519, ITU-T X.520, ITU-T X.521, ITU-T X.525, and ITU-T X.530, the 2000 edition of ITU-T X.509, and
parts 1-10 of the ISO/IEC 9594:2001 edition.
This Directory Specification uses the term fifth edition systems to refer to systems conforming to the fifth edition of the
Directory Specifications, i.e., the 2005 edition of the ITU-T X.500-series Recommendations and the
ISO/IEC 9594:2005 edition.
This Directory Specification uses the term sixth edition systems to refer to systems conforming to the sixth edition of
the Directory Specifications, i.e., the 2008 edition of the ITU-T X.500-series Recommendations and the
ISO/IEC 9594:2008 edition.
This Directory Specification uses the term seventh edition systems to refer to systems conforming to the seventh edition
of the Directory Specifications, i.e., the 2012 edition of the ITU-T X.500-series Recommendations and the
ISO/IEC 9594:2014 edition.
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
4 Rec. ITU-T X.525 (10/2012)
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.
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.
Rec. ITU-T X.525 (10/2012) 5
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).
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 is replicated by protocol exchange
between the shadow supplier and the shadow consumer. The information to be shadowed is all or a subset of the
information held by the shadow supplier's DSA information tree. The shadow consumer's shadowed information
becomes part of its DSA information tree.
To use the Directory information shadow service, the administrative authorities of two DSAs must first reach an
agreement on the terms under which shadowing will take place. This agreement, and the technical specification related
6 Rec. ITU-T X.525 (10/2012)
to this agreement (the shadowing agreement), is discussed in 7.1. A description of the manner in which shadowed
information is represented for the purposes of shadowing is provided in 7.2. The actual transfer of this shadowed
information from the shadow supplier to the shadow consumer is accomplished by means of a set of shadow operations,
which are introduced in 7.3.
The use of shadowed information to satisfy Directory requests is described in Rec. ITU-T X.518 | ISO/IEC 9594-4.
7.1 Shadowing agreement
Before shadowing can occur, an agreement for shadowing is established between the administrative authorities of the
Directory management domains involved in the shadowing. This agreement for shadowing may be multilateral with
respect to DSAs, in that it may cover all shadowing permitted among the set of DSAs concerned. The agreement may
include any set of terms acceptable to the administrative authorities. For example, the agreement may specify policy
information related to security, charging, or other special conditions.
A shadowing agreement is the specific agreement for a particular instance of shadowing between a pair of DSAs (the
shadow consumer DSA and the shadow supplier DSA). This agreement may be explicit (e.g., contractual) or implicit
(e.g., covered by the general terms of an agreement for shadowing as defined above). Each shadowing agreement has a
unique identifier used in all protocol exchanges associated with the agreement. Other parameters of a shadowing
agreement include a specification of the unit of replication, the update mode and possibly the access point of the master
DSA for the shadowed information. Access control information is always included in shadowed information and
therefore need not be explicitly specified.
Initially, the representation of the shadowing agreement within a DSA (shadow supplier or shadow consumer) is created
by an off-line administrative process. It represents essentially a template whose technical parameter values are
subsequently validated during the initiating phase of the agreement and possibly modified during modification
operations on the agreement. The method of storing this agreement is beyond the scope of this Directory Specification.
Some technical aspects of the shadowing agreement may be exchanged via protocol and are discussed in detail in
clause 9.
Although the shadowing agreement will normally provide a true representation of the technical parameters related to the
Directory information shadow service, there may be exceptional cases in which policy overrides the technical
specification resulting in a service inconsistency. For example, there may be certain attributes or attribute values that are
withheld for security reasons. It may be the case that security policy prevents disclosing the mere existence of these
attributes, in which case it would be a violation to represent in the shadowing agreement the fact that they are being
withheld. In this type of situation, the behaviour of the shadow supplier DSA will be as if the technical specification
were a true representation. Thus, users with access to the sensitive data will receive different views of the affected
entries, depending on whether they access the master or a shadow consumer.
7.2 Shadowed information
Shadowed information is the logical set of information which is replicated by the shadow consumer. A replicated area is
a subtree of the DIT defined for purposes of shadowing. The three components of shadowed information are:
a) Prefix information: Information relevant to entries within the replicated area which, with respect to the
DSA information model, is positioned between the area prefix and the root DSA-specific entry (DSE).
This may contain administrative entry and subentry information.
b) Area information: Information about DSEs whose names fall within the replicated area.
c) Subordinate information: Information about knowledge references subordinate to the replicated area.
Figure 3 illustrates the derivation of shadowed information.
Rec. ITU-T X.525 (10/2012) 7
Figure 3 – Shadow supplier derivation of shadowed information
As illustrated at the left of Figure 3, the replicated area is always fully contained within a single naming context. The
root of the subtree representing the replicated area is called the replication base entry. Subordinate knowledge may also
be replicated. Implicit in the subordinate knowledge is the access control information which governs access to the
relative distinguished name (RDN) of the subordinate knowledge. When the subordinate entry is an administrative point
in another DSA, then part of this access control information may be held in prescriptiveACI in subentries beneath
the subordinate knowledge. This knowledge, the refined replicated area, and the area prefix constitute the unit of
replication. This means that the specification of a unit of replication may extend beyond the naming context; however,
the replicated area itself is limited to the naming context. From this unit of replication specification, the shadow supplier
can derive a representation of the shadowed information, which, as shown at the right of the figure, includes the prefix
information, the area information (representing information held by DSEs in the replicated area), and (optionally)
subordinate information. This shadowed information is subsequently conveyed by protocol to the shadow consumer
which then integrates the information into its own DSA information tree. The shadowed information is built out of
shadowed DSEs (SDSEs), which are discussed in 7.2.1. The establishment of shadowed information is discussed in
7.2.2.
Figure 4 illustrates the derivation of shadowed information where extended knowledge is included.
8 Rec. ITU-T X.525 (10/2012)
Figure 4 – Shadow supplier derivation of shadowed information with extended knowledge
7.2.1 Shadowed DSA-Specific Entries (SDSEs)
Shadowed DSA-specific entry (SDSE): That information being shadowed that is associated with a specific name. The
SDSE represents the information shadowed from a DSE in the shadow supplier to a DSE in the shadow consumer, and
is therefore not part of the DSA Information Model.
An SDSE is analogous to a DSE and consists of:
– SDSE type (always);
– user attributes (derived from entry information for DSEs corresponding to entries that are to be
shadowed);
– operational attributes (present as required);
– subordinate-completeness flag (for area and subordinate information only);
– attribute-completeness flag (present for area information only);
– attribute-values-incomplete flag (present for area information only).
7.2.1.1 SDSE type
DSE types are defined in Rec. ITU-T X.501 | ISO/IEC 9594-2. SDSE type, as specified in 11.3.1.1, is analogous to DSE
type, but has fewer relevant options: root, glue, cp, entry, alias, subr, nssr, admPoint, subEntry and sa.
7.2.1.2 Subordinate-completeness flag
The subordinate-completeness flag is a Boolean that is present for SDSEs within the area information and subordinate
information. If the shadow supplier does not intend to provide information about subordinate completeness, the value
FALSE is used for each SDSE. Otherwise the flag has the following semantics:
The flag is TRUE only if one of the following conditions is met for a particular SDSE:
a) it represents a leaf entry;
b) the replicated area contains SDSEs for each subordinate entry and each subordinate reference known to
the master DSA, and if the SDSE represents an NSSR, this knowledge is represented in the SDSE.
The flag is FALSE if one of the following conditions is met for a particular SDSE:
a) the subordinates known to the master for that particular SDSE are not all present in the shadowed
information;
b) in the case of a shadow supplier DSA performing secondary shadowing, if its shadow supplier had set
the flag to FALSE or if its shadow supplier had set the flag to TRUE and the secondary shadow supplier
chooses to set its to FALSE.
Rec. ITU-T X.525 (10/2012) 9
7.2.1.3 Attribute-completeness flag
The attribute-completeness flag is a Boolean and is TRUE if, and only if, all user attributes of the entry, all relevant
collective attributes, all values of such user or collective attributes, and all context information associated with those
values, are present for the SDSE. It is only present for SDSEs containing entry information.
The attribute-completeness flag is not used with respect to Directory operational attributes; it is always assumed that
they are not all present in the SDSE.
7.2.1.4 Attribute-values-incomplete flag
The attribute-values-incomplete flag is a list of the attribute types present in the SDSE for which not all attribute values
are present in the SDSE. It is only present for SDSEs containing entry information.
NOTE – Attribute values may be missing because of selective shadowing based on contexts.
7.2.2 Establishment of shadowed information
The shadowed information represents three basic types of information: prefix information, area information, and
subordinate information. Each of these is discussed in the following subclauses.
7.2.2.1 Prefix information
If the replicated area does not start immediately below the root of the DIT, the shadowed information will include
SDSEs for each entry that is part of the area prefix of the replicated area (the path down from the root of the DIT to, but
not including, the replication base entry, and any relevant subentries). SDSEs for prefix information are constructed as
shown below.
a) If the DSE is an administrative point that has attributes pertaining to the replicated area, or that has one
or more associated subentries whose subtree scope includes some or all of the replicated area, the SDSE
is of type admPoint. If the DSE is also of type cp, the corresponding SDSE is of additional type cp.
Any attributes that are relevant for the replicated area are included in the SDSE. The
administrativeRole attribute shall be included in all administrative point SDSEs which are relevant
to the shadowed information.
b) For subentries below the administrative point for which the subtree scope includes some or all of the
replicated area, SDSEs of type subentry may be included in the shadowed information. If the subtree
scope of such a subentry does not include the replicated area or parts of it, no SDSE for this subentry
need be included. Collective attributes, schema and access control information selected for the area
information are represented in SDSEs of type subentry.
c) There is an empty SDSE of type root for the root DSE.
d) If the DSE is only of type cp, the SDSE is of type cp.
e) All other DSEs not described in a), b), c), or d) are represented as SDSEs of type glue and will only
represent the RDN of the entry.
There are no subordinate-completeness flags in area prefix SDSEs.
7.2.2.2 Area information
All entries in the shadow supplier information tree that are included in the replicated area are represented in the
shadowed information as SDSEs of type entry (unless removed by filtering). These SDSEs contain the attributes of the
entries as selected by the attribute selection of the shadowing agreement. Collective attributes held in subentries are
selected in the same manner as other attributes and are represented in SDSEs of type subentry. If any attributes of an
objectClass attribute and the relevant entry access control
entry have been selected for inclusion in the shadow, the
information will be included in the SDSE for that entry. The attribute-completeness flag is set to indicate whether all
user attributes in the DSE and all relevant collective attributes are present for the SDSE. The collectiveExclusions
operational attribute, if present, is always included in the SDSE.
If the DSE is of type admPoint, the corresponding SDSE is of additional type admPoint and SDSEs of type
subentry for all relevant subentries immediately subordinate to the administrative point DSE are included in the
shadowed information. The rules for inclusion of subentries are stated in 7.2.2.1.
If the DSE is of
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