Home > Articles > Operating Systems, Server > Microsoft Servers

Understanding Active Directory, Part II

  • Print
  • + Share This
The two primary Active Directory components are its logical and physical structures, which respectively involve the organization and communication of objects. A third component, known as the schema, defines objects that make up the Active Directory.
Like this article? We recommend

The two primary Active Directory components are its logical and physical structures, which respectively involve the organization and communication of objects. A third component, known as the schema, defines objects that make up the Active Directory. The discussion of the schema is included in the logical structure section for the sake of convenience.

Logical Structure

The base logical components of the Active Directory are objects and their associated attributes. Object classes are merely definitions of the object types that can be created in the Active Directory. The schema is the Active Directory mechanism for storing object classes. It also permits the addition of other object classes and associated attributes.

Active Directory objects are organized around a hierarchical domain model. This model is a design facility that permits the logical arrangement of objects within administrative, security, and organizational boundaries. Each domain has its own security permissions and unique security relationships with other domains. The Active Directory utilizes multi-master replication to communicate information and changes between domains.

The following sections provide an overview of domain model building blocks: domains, domain trees, forests, organizational units, and the schema.

Domains

The Active Directory manages a hierarchical infrastructure of networked computers with the domain as the foundation. A domain comprises computer systems and network resources that share a common logical security boundary. It can store more than 17 terabytes within the Active Directory database store. Although a domain can cross physical locations, all domains maintain their own security policies and security relationships with other domains. They are sometimes created to define functional boundaries such as an administrative unit (for example, marketing versus engineering). They are also viewed as groupings of resources or servers that utilize a common domain name, known as a namespace. For example, all servers or resources in the EntCert.com namespace belong to a single domain.

In very simple terms, every domain controller has the following information as part of its Active Directory:

  • Data on every object and container object within the particular domain

  • Metadata about other domains in the tree (or forest) to provide directory service location

  • Listing of all domains in the tree and forest

  • Location of the server with the Global Catalog

Domain Trees

When multiple domains share a common schema, security trust relationships, and a Global Catalog, a domain tree is created—defined by a common and contiguous namespace. Thus, for example, all domains with the ending namespace of EntCert.com belong to the EntCert domain tree. A domain tree is formed through the expansion of child domains such as Sales.EntCert.com or Research.EntCert.com. In this example, the root domain is EntCert.com.

The first created domain, known as the root domain, contains the configuration and schema data for the tree and (as we shall see) the forest. A tree structure is formed by adding child domains. There are a number of reasons for creating multiple domains in a tree—for example, some are the following:

  • Discretely managing different organizations or providing unit identities

  • Enforcing different security boundaries and password policies

  • Requiring a better method of controlling Active Directory replication

  • Better handling of a very large number of managed objects

  • Decentralizing administration

A single domain contains a complete Active Directory partition for all of its objects. It is also, by definition, a complete domain tree. As child domains are added to the domain tree, Active Directory partitions are replicated to one or more domain controllers within each of the domains.

Domain Forests

Trust relationships can be formed between domain trees with different namespaces. When this occurs, a domain forest is created, which allows the enterprise to have different domain names, such as "entcert.com" and "unint.com."

All trees within the forest share a number of common attributes, including a Global Catalog, configuration, and schema. A forest is simply a reference point between trees, and does not have its own name. Forests utilize the Kerberos security technology to create transitive trust relationships between trees.

Organizational Units

Domains and child domains can be internally divided into administrative substructures known as organizational units (OUs), each of which can compartmentalize more than 10 million objects. As container objects, OUs can be nested within other OUs. For example, the marketing division may be defined as an organizational unit, and product groups within this division may be defined as suborganizational units. A domain usually comprises one or more organizational units arranged hierarchically. Objects can be organized within organizational units for administrative purposes. The OU acts as a container that lists the object contents, including users, computer systems, and devices such as printers.

An organizational unit is a logical subset defined by security or administrative parameters. In this administrative arrangement, the specific functions of the system administrator can also be easily segmented or delegated with the organizational unit level. From a system administrator's vantage point, this is very important to understand. It is possible to delegate system management responsibility solely to certain activities within a domain, OU, or child subsidiary OU. For example, a person within an organizational unit can be granted authority to manage print and file server functions, but be denied authority to add, modify, or delete user accounts.

Organizational units are subunits with a domain or child domain.

Trees and Forest Scaling and Extensibility

The Active Directory scales across environments ranging from a single server to a domain of one million users or more. The basis of this scaling is the peer-to-peer directory service relationship that is established between domains. Every domain server (known as a domain controller) is provided updated information on Active Directory objects. Consistency across domains is ensured through the automatic replication services. To avoid extremely large and unwieldy directories, the Active Directory creates tree partitions that comprise small portions of the entire enterprise directory. However, every directory tree has sufficient information to locate other objects in the enterprise. In addition to greater efficiency, objects that are more frequently used are placed in the local store for more rapid access. A trust relationship is automatically established between the domains in the same tree, so it is possible to transparently locate resources anywhere in the tree or forest enterprise where the Active Directory resides.

Schema

The schema is simply a framework of definitions that establishes the type of objects available to the Active Directory. These definitions are divided into object classes, and the information that describes the object is known as its attributes. There are two types of attributes: those that must exist and those that may exist. For example, the schema defines a user object class as having the user's name as a required attribute; the user's physical location or job description is optional. Attributes are used to further help distinguish one object from another. They include Object Name, Object Identifier (OID), Syntax, and Optional Information.

The schema is stored within the Active Directory database file Ntds.dit. Object definitions are stored as individual objects, so the Directory can treat schema definitions in the same way it treats other objects. The default schema is created with the first installation of the Active Directory. It contains common objects and properties for items such as users, groups, computers, printers, and network devices. It also establishes the default Active Directory structure that is used internally.

As an extensible component, new object classes may be dynamically added to the current schema, and old object classes can be modified. It is not possible to modify or deactivate system classes and attributes.

NOTE

Schema data should not be confused with configuration data, which provides the structural information for the Active Directory. The schema provides information about what objects and attributes are available to the Directory. Configuration information maintains the Directory structure that represents the relationship between the actual objects, and indicates how to replicate this structure between domain controllers.

The schema is accessible only to the Administrators and Schema Admins user groups by default. It is managed through the Active Directory Schema snap-in tool. (The Active Directory Schema snap-in becomes available only after the adminpak application is installed from the Windows 2000 Server CD within the I386 folder.) Active Directory schema elements are dynamic and available to applications after the initial startup of the system. New attributes and classes can be added to the schema to provide dynamic extensibility to the Active Directory.

The schema object container attaches definitions to the directory tree. It is typically represented as a child of the directory root. In turn, each instance has its own individual schema.

The schema operations master domain controller manages the structure and content of the schema. It replicates schema information to the other domain controllers in the forest. Every domain controller loads a copy of the schema in a RAM-based cache, ensuring rapid access to currently used object and attribute definitions. If changes occur in the schema, the cache is refreshed.

In the third article of this series, we examine the physical structure of active directory.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020