Free Active Directory Tutorial

Ref : www.Learnthat.com

What is Active Directory?

Like other directory services, such as Novell Directory Services (NDS), Active Directory is a centralized and standardized system that automates network management of user data, security and distributed resources and enables interoperation with other directories.

Active Directory is designed especially for distributed networking environments.

AD is functionally a place to store information about people, things (computers, printers, etc), applications, domains, services, security access permissions, and more. Applications and services then use the directory to perform a function.

For example, Microsoft Windows uses Active Directory information to allow a user to

login to their computer and provide access to the security rights assigned in Active

Directory. Windows is accessing the directory and then providing rights based on what it

finds. If a user account is disabled in Active Directory, the directory itself is just setting a

flag which Windows uses to disallow a user from logging in.

We mentioned in the introduction that administrators use Active Directory to deploy

software – this is an incomplete description. Administrators can set policies and

information that a certain software application should be deployed to a certain user –

AD itself does not deploy the software, but a Windows service reads the information

from Active Directory and then installs the software.

Introduced in 2000 server and further enhanced for windows server 2003, provides a single reference, called a directory service, to all the objects in a network, including users, groups, computers, printers, policies and permissions.

Active Directory (AD) is a technology created by Microsoft to provide network services

including LDAP directory services; Kerberos based authentication, DNS naming, secure

access to resources, and more. Active Directory uses a single Jet database which a variety of

services and applications can use to access and store a variety of information. Active

Directory is used by system administrators to store information about users, assign security

policies, and deploy software. AD is used in many different types and size of environments

from the very small (a dozen users) to hundreds of thousands of users in a global

environment.

In this tutorial, you will learn the basic structure of Active Directory, gain an understanding

of how Active Directory works, learn how to install Active Directory, and learn the

components of AD.

This tutorial is divided into these sections:

Why implement Active Directory?

First and foremost, Microsoft Active Directory is generally considered to be a significant improvement over Windows NT Server 4.0 domains or even standalone server networks. Active Directory has a centralized administration mechanism over the entire network. It also provides for redundancy and fault tolerance when two or more domain controllers are deployed within a domain.

Active Directory automatically manages the communications between domain controllers to ensure the network remains viable. Users can access all resources on the network for which they are authorized through a single sign-on. All resources in the network are protected by a robust security mechanism that verifies the identity of users and the authorizations of resources on each access.

History of Active DirectoryActive Directory was introduced to the world in the mid-1990s by Microsoft as a

replacement for Windows NT-style user authentication. Windows NT included a flat and

non-extensible domain model which did not scale well for large corporations. Active

Directory, on the other hand, was created as a true directory service versus a flat user-

management service that NT had. Though it was introduced in the 1990s, it did not

become a part of the Operating System until Windows 2000 Server was released in

2000. Since then, Windows Server 2003 and Server 2008 have been introduced and

Active Directory has gone under some expansion.

This tutorial is based on Windows Server 2003 as it is currently the most widely installed

version of the Windows network Operating System (NOS), though in the future we will

release versions for Windows Server 2008 and future Windows releases as it becomes

necessary. Though this tutorial is not focused on Windows Server 2008, much of the

basic knowledge and instruction relates to either OS.

LDAP

Active Directory and LDAP

Microsoft includes LDAP (Lightweight Directory Access Protocol) as part of Active Directory. LDAP is a software protocol for enabling anyone to locate organizations, individuals and other resources such as files and devices in a network, whether on the public Internet or on a corporate intranet.

In a network, a directory tells you where in the network something is located. On TCP/IP networks (including the Internet), the domain name system (DNS) is the directory system used to relate the domain name to a specific network address (a unique location on the network). However, you may not know the domain name. LDAP allows you to search for individuals without knowing where they're located (although additional information will help with the search).

An LDAP directory is organized in a simple "tree" hierarchy consisting of the following levels:

The root directory (the starting place or the source of the tree), which branches out to Countries, each of which branches out to Organizations, which branch out to

Organizational units (divisions, departments and so forth), which branch out to (include an entry for) Individuals (which include people, files and shared resources, such as printers)

An LDAP directory can be distributed among many servers. Each server can have a replicated version of the total directory that is synchronized periodically.

It is important for every administrator to have an understanding of what LDAP is when searching for information in Active Directory and to be able to create LDAP queries is especially useful when looking for information stored in your Active Directory database. For this reason, many admins go to great lengths to master the LDAP search filter.

Active Directory is based loosely on LDAP – Lightweight Directory Access Protocol – an

application protocol for querying and modifying directory services developed at the

University of Michigan in the early 1990s. An LDAP directory tree is a hierarchical

structure of organizations, domains, trees, groups, and individual units.

Example of an LDAP Tree

Active Directory StructureUnlike Windows NT, Active Directory is designed for you to create a functional and

usable hierarchy for your environment. Not only does this make the environment look

cleaner, but it also allows central system administrators to delegate specific authority

over areas to other administrators, team members, and groups. AD has a very flexible

structure, allowing you to build a hierarchy in whatever way you wish – one big unit,

broken down by geographic location, by department, by astronomical sign, or however

you desire.

Achieving this flexibility in hierarchical design is a defined structure. The structure of

Active Directory starts with forests and domains and goes down to organizational units

and individual objects (such as a user or computer account).

Basic Active Directory ComponentsIt provides the basic building blocks for people to build their own directory. These basic

building blocks of Active Directory include domains, domain controllers, trusts, forests,

organizational units, groups, sites, replication, and the global catalog.

Forests: The collection of every object, its attributes and attribute syntax in the Active Directory.Domain: A collection of computers that share a common set of policies, a name and a database of their members.Organizational units: Containers in which domains can be grouped. They create a hierarchy for the domain and create the structure of the Active Directory's company in geographical or organizational terms.Sites: Physical groupings independent of the domain and OU structure. Sites distinguish between locations connected by low- and high-speed connections and are defined by one or more IP subnets.

Understanding Forests

At the top of the Active Directory structure is a forest. A forest holds all of the objects,

organizational units, domains, and attributes in its hierarchy. Under a forest are one or

more trees which hold domains, OUs, objects, and attributes.

Forests are not limited in geography or network topology. A single forest can contain numerous domains, each sharing a common schema. Domain members of the same forest need not even have a dedicated LAN or WAN connection between them. A single network can also be the home of multiple independent forests. However, additional forests may be desired for testing and research purposes outside of the production forest.

As illustrated in this image, there are two trees in the forest. You might use a structure

like this for organizations with more than one operating company.

You could also design a structure with multiple forests, but these are for very specific

reasons and not common.

Domains

At the heart of the Active Directory structure is the domain. The domain is typically of

the Internet naming variety (e.g. Learnthat.com), but you are not forced to stick with

this structure – you could technically name your domain whatever you wish.

Microsoft recommends using as few domains and possible in building your Active Directory structure and to rely on Organizational Units for structure. Domains can contain multiple nested OUs, allowing you to build a pretty robust and specific structure. Domains serve as containers for security policies and administrative assignments. All objects within a domain are subject to domain-wide Group Policies by default. Likewise, any domain administrator can manage all objects within a domain. Furthermore, each domain has its own unique accounts database. Thus, authentication is on a domain basis. Once a user account is authenticated to a domain, that user account has access to resources within that domain.

Domain Controllers

In Windows NT, domains used a Primary Domain Controller (PDC) and Backup Domain

Controller (BDC) model. This had one server, the PDC, which was “in charge” while the

other DCs where subservient. If the PDC failed, you had to promote a BDC to become

the PDC and be the server in charge.

In Active Directory, you have multiple Domain Controllers which are equal peers. Each

DC in the Active Directory domain contains a copy of the AD database and synchronizes

changes with all other DCs by multi-master replication. Replication occurs frequently

and on a pull basis instead of a push one. A server requests updates from a fellow

domain controller. If information on one DC changes (e.g. a user changes their

password), it sends signal to the other domain controllers to begin a pull replication of

the data to ensure they are all up to date.

Servers not serving as DCs, but in the Active Directory domain, are called ‘member

servers.’

Organizational Units

Organizational units are much more flexible and easier overall to manage than domains. OUs grant you nearly infinite flexibility as you can move them, delete them and create new OUs as needed. However, domains are much more rigid in their existence. Domains can be deleted and new ones created, but this process is more disruptive of an environment than is the case with OUs and should be avoided whenever possible.

An Organizational Unit (OU) is a container which gives a domain hierarchy and

structure. It is used for ease of administration and to create an AD structure in the

company’s geographic or organizational terms.

Organizational Units

An OU can contain OUs, allowing for the creating of a multi-level structure, as shown in

the image above. There are three primary reasons for creating OUs:

Organizational Structure: First, creating OUs allows a company to build a structure in

Active Directory which matches their firm’s geographic or organizational structure. This

permits ease of administration and a clean structure.

Security Rights: The second reason to create an OU structure is to assign security

rights to certain OUs. This, for example, would allow you to apply Active Directory

Policies to one OU which are different than another. You could setup policies which

install an accounting software application on computers in the Accounting OU.

Delegated Administration: The third reason to create OUs is to delegate

administrative responsibility. AD Architects can design the structure to allow local

administrators certain administrative responsibility for their OU and no other. This

allows for a delegated administration not available in Windows NT networks.

Sites

By definition, sites are collections of IP subnets that have fast and reliable communication links between all hosts. Another way of putting this is a site contains LAN connections, but not WAN connections, with the general understanding that WAN connections are significantly slower and less reliable than LAN connections. By using sites, you can control and reduce the amount of traffic that flows over your slower WAN links. This can result in more efficient traffic flow for productivity tasks. It can also keep WAN link costs down for pay-by-the-bit services.

An Active Directory site object represents a collection of IP subnets, usually constituting

a physical Local Area Network (LAN). Multiple sites are connected for replication by site

links. Typically, sites are used for:

Physical Location Determination: Enables clients to find local resources such as

printers, shares, or domain controllers.

Replication: You can optimize replication between domain controllers by creating links.

By default, Active Directory uses automatic site coverage, though you can purposefully

setup sites and resources.

Groups

Groups serve two functions in Active Directory: security and distribution.

A security group contains accounts which can be used for security access. For

example, a security group could be assigned rights to a particular directory on a file

server.

A distribution group is used for sending information to users. It cannot be used for

security access.

There are three group scopes:

Global: Global scope security groups contains users only from the domain in which is

created. Global security groups can be members of both Universal and Domain Local

groups.

Universal: Universal scope security groups can contain users, global groups, and

universal groups from any domain. These groups are typically used in a multi-domain

environment if access is required across domains.

Domain Local: Domain Local scope groups are often created in domains to assign

security access to a particular local domain resource. Domain Local scope groups can

contain user accounts, universal groups, and global groups from any domain. Domain

Local scope groups can contain domain local groups in the same domain.

Trust Relationships

Trust Relationships are important in an Active Directory environment so forests and

domains can communicate with one another and pass credentials. Within a single

forest, trusts are created when a domain is created. By default, domains have an

implicit two-way transitive trust created. This means each domain trusts each other for

security access and credentials. A user in domain A can access resources permitted to

him in domain B while a user in domain B can access resources permitted to her in

domain A.

AD allows several different types of trusts to be created, but understanding the two-way

transitive trust is the most important to understanding AD.

Replication

Understanding Active Directory replication

Active Directory replication is key to the health and stability of an Active Directory environment. Without proper and timely replication, a domain will be unable to function effectively. Replication is the process of sending update information for data that has changed in the directory to other domain controllers. It is important to have a firm understanding of replication and how it takes place, both within the domain and in multiple-site environments.

There are three main elements or components that are replicated between domain controllers: the domain partition replica, the global catalog and the schema.

The domain partition replica is the Active Directory database of a domain. Each domain controller maintains a duplicate copy of its local domain partition replica. Domain controllers do not maintain copies of replicas from other domains. When an administrator makes a change to the domain, that change is replicated to all domain controllers immediately.

Each forest contains only a single global catalog. By default, the first domain controller installed into a forest is the global catalog server. The global catalog contains a partial replica of every object within each domain of the forest. The global catalog serves as a master index for the forest, which allows for easy and efficient searching for users, computers, resources and other objects. Any domain controller can be configured to act as a peer global catalog server. You should have at least two global catalog servers per domain and at least one per site. As changes are made to objects within the forest, the global catalog is updated. Once the global catalog is changed on one domain controller, it is replicated to all other domain controllers in the forest.

Every domain controller in a forest has a copy of the schema. Just as with changes to the Active Directory database (i.e., domain partition replica), any changes to the Active Directory schema are replicated to all other domain controllers in the forest. Fortunately, the schema is usually static so there is little replication traffic caused by schema changes.

Multi-master replication

Within Windows-based Active Directory domains, each domain controller is a peer server. Each domain controller has equal power and responsibility to support and maintain the Active Directory database. It is this database that is essential to the well-being and existence of the domain itself. This is such an important task that Microsoft elected to make it possible to deploy multi-redundant systems to support Active Directory by making each domain controller a peer.

Whenever a change occurs to any object within an Active Directory domain, that change is replicated automatically to all domain controllers within the domain. This process is called multi-master replication. Multi-master replication does not happen instantly across all servers simultaneously. Rather, it is a controlled process where each domain controller peer is updated and validated in a logically controlled procedure.

As an administrator, you have some control over how multi-master replication occurs. Most of your control is obtained through the use of sites. A site is a logical designation of domain controllers in a network that are all located within a defined physical area. In most cases, sites control traffic over high-expense low-bandwidth WAN links. When a domain exists on two or more sites, normal Active Directory replication between the domain controllers in different sites is terminated. Instead, a single server within each site, labeled as a bridgehead server, performs all replication communications. You can configure this bridgehead server for when replication is allowed to occur and how much traffic it can generate when performing replication.

You can use sites to control replication even if you do not employ WAN links on your network. Sites effectively give administrators control over how and when AD multi-master replication occurs within their network.

Active Directory replication topology design

One of the secrets to an efficient and error-free Active Directory infrastructure is a well-designed replication topology. While this can be easy to design in a simple network, a large, complex network presents a challenge. Designing the AD topology efficiently is to construct it so that it takes advantage of the strengths and minimizes the weaknesses of the network. In a complex network, you are likely to have a number of different link speeds connecting remote sites.

The best practices for Active Directory replication design include:

1. Design the AD topology to take advantage of the network topology and link speeds.2. Define lower speed links with higher cost site links. The cost of the links reduces as you get to

faster areas in the topology.

3. Avoid "dead spots" -- all sites must connect to each other eventually. I have seen some topologies that left certain sites isolated because they didn't design the site links to connect them.

4. Site links should only have two sites per link. The exception to this is the Core site link which can have more. Defining more than two sites per link can result in unpredictable results when a DC failure occurs.

5. Diagram the overall flow of replication (like the figures here). You can use sophisticated features available in tools like HP OpenView (see the example in Figure 3) or Microsoft MOM, or you can simply draw it in a PowerPoint slide as I did in Figure 2. You'd be surprised at how many errors you will find by making a drawing of the topology.

6. Don't define scheduling unless you really have a good reason, and then you should test it thoroughly. Since you can schedule replication over the site link as well as the connection object itself, and since the resultant replication schedule is a merge of the two, you can end up with a schedule that prohibits replication. You also define replication frequency, which further complicates it. For instance, if you schedule the site links to replicate Monday through Friday from 8 a.m. to 6 p.m., and then have some connection objects that only replicate Tuesday and Thursday from 6 p.m. to 10 p.m., those connection objects will never replicate. Unless you have a very slow or limited network (such as VPN links), you should avoid this level of manual intervention.

7. Run the AD in Windows 2003 Forest mode. This means all DCs are at Windows Server 2003, and all domains are running in Windows 2003 mode. This takes advantage of the new spanning tree and compression algorithms available in Windows Server 2003, as well as other features that make replication much more efficient than were available in Windows 2000.

8. Monitor the AD. Once you get it in place, monitor it. One of the easiest ways to monitor it, outside of using Microsoft or third-party tools, is using the Repadmin tool and its "Replsum" option: Repadmin /replsum /bydest /bysrc /sort:delta. This will provide a nice, neat table of all DCs in all domains in the forest, telling you how long it has been for outbound and inbound replication (i.e. where each DC appears as a source and destination). Watching this over several days will give you a chance to find any holes in the topology.

Troubleshooting Active Directory replication

Replication should occur automatically. When it doesn't, the best solution isn't just to force Active Directory replication, but to check out the topology. If the replication topology has become unstable or misconfigured, it needs to be corrected before initiating a manual replication procedure.

The Knowledge Consistency Checker (KCC) creates the replication topology used for intra-site replication automatically. Rather than creating a full mesh for replication, the KCC designs a topology where every DC has at least two replication partners and is no more than three hops away from any other DC. With such a topology, every DC can be fully updated with as little as three replication cycles.

The REPAdmin tool from the Windows Support Tools and Resource Kit can be used to check the topology. The command "repadmin /showreps" runs on a domain controller and produces a list of replication partners as designated by the KCC. To check the topology, verify that every DC lists at least two replication partners and that all named

partners see each other as partners. For example, if Server A lists Server B and C as partners, then both Server B and C should list Server A in return as a partner. If you discover a problem or inconsistency in the topology, use the KCC to regenerate the topology.

Once you are sure the topology is correct, then and only then should you force Active Directory replication.

Debugging replication errors

The lion's share of Active Directory problems are to some degree caused by replication failures, and one of the most notorious replication errors is the Event ID 1311.

The first step in resolving this replication error is to determine the scope of the error. The easiest way to do this is with the Repadmin/Replsum command. This will give you a complete summary of all the DCs in the forest, including the relevant event ID if it is in an error state. The general form of the command is this:

Repadmin /Replsum /bysrc /bydest /sort:delta

Here is a sample output of this command. Note that there are four domain controllers failing replication. While the 1311 may not show up in the output of this command, it is common for it to be paired up with the 1722 event (which basically means no physical connectivity). Obviously, if there is no physical connectivity (which would mean there was a network failure), replication isn't going to happen. The first thing to do is to check the general health of the domain using theRepadmin /replsum command just described. You can also ping broken DCs by address and FQDN, and you can run NetDiag and DCDiag commands from the command line (with the /v switch on each). This will give you more details about the errors and perhaps related ones.Note: The network connecting all the sites should be fully routed. Don't create a site link if there is no underlying network link to get between the sites in the site link.Logical connectivity is a bit more difficult to diagnose. It means, bottom line, that something in the AD site topology configuration is wrong, creating a hole in the topology. This could be solved by one of the following actions: configuring a preferred bridgehead server, making sure all sites are defined in site links and making sure there is a complete mesh of sites in site links.

DNS also must be taken into account. Since Active Directory replication relies on DNS name resolution to find DCs to replicate with, if DNS is broken, it could cause the 1311 events to occur. The helpful thing here is that if DNS is the culprit, the 1311 event will have the phrase "DNS Lookup Failure" included in the description. If you see this phrase, then you absolutely, positively have a DNS problem that must be fixed.

When debugging 1311 events, you should get a scope of the entire forest to see which DCs are not replicating. You can do this easily using the Repadmin /Replsum command. Note that the loss of physical connectivity, an incomplete AD site topology or DNS failure usually cause these events, with an outside chance it will be an orphaned object (an object that connot be found in the directory tree). Usually, other events will accompany them, such as the 1722 (RPC Server Unavailable), or the event will contain a descriptive statement such as "DNS Lookup Failure." This is a critical event that must be resolved in order for Active Directory replication to function properly to all DCs.

Since most Active Directory networks contain multiple domain controllers and users

could theoretically attach to any DC for authentication or information, each of the

servers needs to be kept up to date. Domain Controllers stay up to date by replicating

the database between each other. It performs this using a pull method – a server

requests new information from a different DC frequently. After a change, the DC

initiates a replication after waiting 15 seconds (in Windows 2003) or 5 minutes (in

Windows 2000). Windows Server 2003 uses technology to only replicate changed

information and compressions replication over WAN links.

Windows Server sets up a replication topology to determine where a server updates

from. In a large network, this keeps replication time down as servers replicate in a form

of a ring network.

Active Directory uses multi-master replication. Multimaster replication does not rely on

a single primary domain controller, but instead treats each DC as an authority. When a

change is made on any DC, it is replicated to all other DCs. Although each DC is

replicated alike, all of the DCs aren’t equal. There are several flexible single-master

operation roles which are assigned to one domain controller at a time.

AD uses Remote Procedure Calls (RPC) for replication and can use SMTP for changes to

schema or configuration.

FSMO Roles

All domain controllers are not equal. We know, it’s hard to hear. You’ve spent this whole

time reading this tutorial thinking that all DCs are created equal and now we have to

burst your bubble. Some DCs have more responsibility than others. It’s just part of life!

There are five roles which are called operations masters, or flexible single-master

operations (FSMOs). Two are forestwide roles and three are domainwide roles.

The forestwide roles are:

Schema master: Controls update to the Active Directory schema.

Domain naming master: Controls the addition and removal of domains from the

forest.

The three domainwide roles are:

RID master: Allocates pools of unique identifier to domain controllers for use when

creating objects. (RID is relative identifier).

Infrastructure master: Synchronizes cross-domain group membership changes. The

infrastructure master cannot run on a global catalog server, unless all of the DCs are

global catalog servers.

PDC Emulator: Provides backward compatibility for NT 4 clients for PDC operations –

such as a password change. The PDC also serves as the master time server.

Global Catalog

As a network gets larger, it can contain multiple domains and many domain controllers.

Each domain only contains records from its own domain in its AD database to keep the

database small and replication manageable. The Active Directory domain relies on

a global catalog database which contains a global listing of all objects in the forest.

The Global Catalog is held on DCs configured as global catalog servers.

The global catalog contains a subset of information – such as a user’s first name and

last name – and the distinguished name of the object so your client can contact the

proper domain controller if you need more information. The distinguished name is the

full address of an object in the directory. For example, a printer in the OU Accounting in

the Learnthat.com domain might have a distinguished name of:

CN=AcctLaser1,OU=Accounting,DC=Learnthat,DC=com

The GC database is only a subset of the entire database called the Partial Attribute Set

(PAS), containing 151 of the 1,070 properties available in Windows Server 2003. You

can define additional properties for replication to the GC by modifying schema.

“Finally, there must be some way for Active Directory services to quickly respond to user queries. Although many user queries pertain to the domain in which the users belong, there are also many queries that are not domain specific, and rather, are made throughout the enterprise. For example, e-mail name queries. A truly enterprise-ready and performance-minded directory service must be able to service such frequent and global queries without generating undue network traffic and without having to jump through multiple query referrals. The answer is a directory catalog that contains a subset of attributes for every object in the enterprise. In effect, it must be a catalog of object attributes that are globally interesting. For Active Directory services, that answer is the Global Catalog. The Global Catalog consists of selected attributes from every object in the enterprise, which means that selected attributes from every object in the forest are available for domain-local querying. Just as Microsoft has created a default set of objects in the schema, default attributes from each schema object are tagged for inclusion in the Global Catalog. (You might never need to modify these—but you can.) Most objects have approximately 15 attributes, and approximately seven of those attributes are tagged for inclusion in the Global Catalog.

The Global Catalog sits on selected domain controllers within each domain and services queries that are specific to global searches. When a user submits a global query based on an object's attribute, and that object's attribute is tagged for inclusion in the Global Catalog, the query can be resolved by a domain controller in the local domain that is configured to keep a copy of the Global Catalog. Because there is at least one domain controller housing the Global Catalog in each domain, queries directed at global searches can be performed and resolved quickly. Attributes included in the Global Catalog by default were chosen because they don't change very often, and that's the way it should be. Using static information in the Global Catalog minimizes replication traffic; after all, when an object's attribute that's tagged for inclusion in the Global Catalog changes, that change must be replicated to all Global Catalog domain controllers across the entire enterprise. Apart from the minimizing of replication traffic, static information in general is more appropriate for global searches.“

The Infrastructure Master and Global Catalog

Among the other key components within Active Directory is the Infrastructure Master. The Infrastructure Master (IM) is a domain-wide FSMO (Flexible Single Master of Operations) role responsible for an unattended process that "fixes-up" stale references, known as phantoms, within the Active Directory database.

Phantoms are created on DCs that require a database cross-reference between an object within their own database and an object from another domain within the forest. This occurs, for example, when you add a user from one domain

to a group within another domain in the same forest. Phantoms are deemed stale when they no longer contain up-to-date data, which occurs because of changes that have been made to the foreign object the phantom represents, e.g., when the target object is renamed, moved, migrated between domains or deleted. The Infrastructure Master is exclusively responsible for locating and fixing stale phantoms. Any changes introduced as a result of the "fix-up" process must then be replicated to all remaining DCs within the domain.

The Infrastructure Master is sometimes confused with the Global Catalog (GC), which maintains a partial, read-only copy of every domain in a forest and is used for universal group storage and logon processing, among other things. Since GCs store a partial copy of all objects within the forest, they are able to create cross-domain references without the need for phantoms.

Group Policy management and Active Directory

It's difficult to discuss Active Directory without mentioning Group Policy. Admins can use Group Policies in Microsoft Active Directory to define settings for users and computers throughout a network. These setting are configured and stored in what are called Group Policy Objects (GPOs), which are then associated with Active Directory objects, including domains and sites. It is the primary mechanism for applying changes to computers and users throughout a Windows environment.

Through Group Policy management, administrators can globally configure desktop settings on user computers, restrict/allow access to certain files and folders within a network and more.

It is important to understand how GPOs are used and applied. Group Policy Objects are applied in the following order: Local machine policies are applied first, followed by site policies, followed by domain policies, followed by policies applied to individual organizational units. A user or computer object can only belong to a single site and a single domain at any one time, so they will receive only GPOs that are linked to that site or domain.

GPOs are split into two distinct parts: the Group Policy Template (GPT) and the Group Policy Container (GPC). The Group Policy Template is responsible for storing the specific settings created within the GPO and is essential to its success. It stores these settings in a large structure of folders and files. In order for the settings to apply successfully to all user and computer objects, the GPT must be replicated to all domain controllers within the domain.

The Group Policy Container is the portion of a GPO stored in Active Directory that resides on each domain controller in the domain. The GPC is responsible for keeping references to Client Side Extensions (CSEs), the path to the GPT, paths to software installation packages, and other referential aspects of the GPO. The GPC does not contain a wealth of information related to its corresponding GPO, but it is essential to the functionality of Group Policy. When software installation policies are configured, the GPC helps keep the links associated within the GPO. The GPC also keeps other relational links and paths stored within the object attributes. Knowing the structure of the GPC and how to access the hidden information stored in the attributes will pay off when you need to track down an issue related to Group Policy.

For Windows Server 2003, Microsoft released a Group Policy management solution as a means of unifying management of Group Policy in the form of asnap-in known as the Group Policy Management Console (GPMC). The GPMC provides a GPO-focused management interface, thus making the administration, management and location of GPOs much simpler. Through GPMC you can create new GPOs, modify and edit GPOs, cut/copy/paste GPOs, back up GPOs and perform Resultant Set of Policy modeling.

Active Directory and the Domain Name System (DNS)

DNSActive Directory is integrated with Domain Naming System (DNS) and requires it to be

present to function. DNS is the naming system used for the Internet and on many

Intranets. You can use DNS which is built into Windows 2000 and newer, or use a third

party DNS infrastructure such as BIND if you have it in the environment. It is

recommended you use Window’s DNS service as it is integrated into Windows and

provides the easiest functionality.

AD uses DNS to name domains, computers, servers, and locate services.

A DNS server maps an object’s name to its IP address. For example, on the Internet, it is

used to map a domain name (such as www.learnthat.com) to an IP address (such as

64.34.165.234). In an Active Directory network, it is used not only to find domain

names, but also objects and their IP address. It also uses service location records (SRV)

to locate services.

What is DNS? One can define the domain name system as the way that Internet domain names are located and translated into Internet Protocol addresses. A domain name is a meaningful and easy-to-remember "handle" for an Internet address.

Active Directory relies heavily on DNS to function, but not just any DNS. Active Directory is highly dependent on the Microsoft DNS service found on Windows 2000 Server or Windows Server 2003 systems or equivalents. However, though not highly recommended, it is possible integrate a non-Microsoft DNS to use with Active Directory.

Microsoft first introduced a DNS service with Windows NT Server 4.0. However, that early version of DNS from Microsoft is not capable of supporting Active Directory. Windows NT Server 4.0 DNS lacks three specific features: Service Resource Records (SRV RR), Dynamic DNS (DDNS) and Incremental Zone Transfers (IXFR). Without these DNS features, Active Directory cannot function. Therfore, it is essential to understand how DNS works.

DNS is extremely important to all aspects of proper Active Directory operation. Any time a client makes a request for a domain service, it must find a domain controller to service that request, which is where DNS comes in to play.

There are two types of DNS queries: recursive and iterative. When a DNS client requests DNS information, it uses a recursive query to do so. (And for the purposes of this discussion, a DNS client is any computer requesting DNS information, even if that computer happens to be running a server operating system.) In a recursive query, the DNS client sends its query to the first DNS server that it has been configured for in its TCP/IP configuration. It then sits and waits for the server to return an answer. If the server returns a positive response, the client will then go to the IP address returned by the server.

If it's a negative response, the client will return some sort of "Page/Resource not found" error to the user. One thing that's important to note here is that configuring multiple DNS servers on a client will not cause the client to check with subsequent servers if the first one returns a negative response. The only time a client will go to its secondary DNS server is if the first one is unavailable. If the first DNS server queried returns a negative response, the client will not try any secondary servers and will accept that negative response as final.

Adhering to proper DNS settings and best practices is crucial to Active Directory processes, such as replication.

DNS server configuration

DNS is fairly simple and straightforward. As long as you follow the basic rules of configuration, DNS will give you few problems. However, there are certain complex configurations that are important to know about and remember when configuring DNS servers, which can allow administrators to get a better handle on options that can make a difference in DNS operation, logging and troubleshooting.

One of the first things to figure out when learning DNS in Active Directory is knowing if a property is that of the DNS server or a zone. Both are exposed in the DNS Management snap-in tool.

Here are a couple of ways to keep them straight:

1. Server properties are general properties that apply to the whole DNS environment, such as Forwarding, Name Servers, root hints and logging.

2. Zone properties are specific properties that vary with the zone, such as dynamic updates, zone type (AD, Standard Primary or Secondary) and replication type.

DNS structure and design

DNS architecture design is also very important. When designing the DNS structure, it is important to keep in mind certain principles and practices that will affect the overall name resolution performance in the network. DNS structures that are patched together or not well thought out will work, but they have pockets of failure that will affect Active Directory performance. That is why adherence to best practices in the DNS structure is extremely important in creating an efficient and productive Active Directory.

One key to designing DNS involves the use of Active Directory integrated zones(ADI). An ADI zone is a writeable copy of a forward lookup zone that is hosted on a domain controller. This is a requirement since the DNS records are all held in Active Directory, thus the DNS server needs access to the AD. Since each DC hosts a writeable copy of the DNS zone, clients (workstations, servers and other DCs) can register their DNS records on a domain controller hosting an ADI primary zone -- usually the DC that authenticated them -- rather than search the network to find a single DNS server (primary) that will add the client's host and resource records.

So how is a DNS structure using Active Directory integrated zones designed? ADI zones can only be hosted on DCs. However, many administrators want to put domain name servers in remote sites to provide better name-resolution performance and to decrease network traffic. That way, users don't have to go across the WAN to find a DNS server. However, an administrator may not want to put a DC in that location. Windows 2000 Server and Windows Server 2003 allow admins to put a standard secondary zone (read only) on a member server and use one of the ADI primary servers as the master.

The rule is that an ADI primary zone can only exist on a DC, but admins can have a standard secondary of that zone on a member server. Thus, clients can connect to their local DNS server whether it is hosting the ADI primary or the secondary. When a client (DC, member server or workstation) tries to register, however, it can only register on a DNS server hosting the ADI primary zone. If the client points to a server hosting a secondary, the client will simply receive a referral to one of the primaries to be registered.

Protecting DNS

DNS security is a major priority. Many of the functions and features of Active Directory use DNS to locate domain controllers, systems, services, clients, and other objects. It should be obvious that protecting DNS is almost as important as protecting Active Directory itself. Basically, if DNS fails, so does Active Directory. This, in turn, means that if DNS fails, an entire network may be disabled.

Providing protection for DNS as a means to provide additional protection for AD DCs is an essential part of establishing a truly secure networking environment. Protecting your DNS servers will require a multi-pronged approach. First and foremost, establish the same secure design, implementation and deployment procedures for your DNS servers as I've recommended for your AD DCs.

Next, consider implementing secured communications with DNS servers, monitor all network traffic, and re-evaluate the open ports on your firewall. By encrypting all communications between DNS servers and all DNS clients (which includes not just end user clients but also Active Directory DCs and member servers), it will minimize or eliminate the possibility of traffic interception and manipulation. One of the best ways to implement this is through IPSec, which is is a framework for a set of protocols for security at the network or packet processing layer of network communication.

Note: While the implementation of IPSec across all systems will likely cause a measurable decrease in the performance of network communications due to the overhead of encrypting and decrypting communications, many experts feel the increased security should more than compensate for the slight reduction in throughput.

It is also important to monitor all network traffic and re-evaluate the open ports on your firewall. By monitoring network traffic, admins should be able to determine when illegitimate or abnormal traffic patterns or content begin to enter their network.

Even with all recommended precautions in place, however, there is still a possibility of a malicious person gaining access to a DNS server. If that happens, admins must rely upon internal DNS security precautions, which include:

Secure dynamic updates  DNS resource record registration quotas  Delegate DNS administration  Use secured routing  Maintain a split DNS namespace  Disable recursion

Troubleshooting DNS

DNS troubleshooting is an absolutely vital process in Active Directory. It is important to keep DNS healthy and to know how to repair it when it breaks.

This article reviews some of the common DNS problems and the tools to use forDNS troubleshooting .

Avoiding Active Directory security breaches

The importance of protecting your Active Directory has already been touched on in reference to DNS security. However, that is just the tip of the iceberg when it comes to maintaining a secure environment.

As far as Active Directory security best practices go, layered security is the best method to use when planning and designing a security solution. Layered security or defense in depth is the simple concept of placing your valued assets at the center of your environment and building or deploying multiple concentric circles or rings of protection around those assets. Thus, violations to confidentiality, integrity, or availability must overcome numerous security restrictions, precautions, and protections before being able to affect your assets.

While Microsoft has increased the default security within Active Directory (especially if you have a Windows Server 2003 Active Directory installation), you still need to consider additional security settings after it is installed.

Securing your domain controllers

One of the first steps you should take involves developing a solid domain controller security policy. Protecting your domain controllers is at the core of protecting your Active Directory investment. Without your domain controllers you won't have your Active Directory network infrastructure. With exposed and unprotected domain controllers you also are at risk for attackers to enumerate shared folders and usernames, giving up valuable information that can be used to further attack the network.

Therefore, it is critical that domain controllers are running and protected in order for the Active Directory environment to remain functioning and stable. To protect domain controllers, you should consider the following areas of security protection:physical access (keeping DCs in a secure location that is only accessible by the IT staff) and network access (protecting DCs from those who might attack your network).

As an administrator, you need to be concerned with making sure internal users have proper access and that potential intruders are frustrated in their attempts to compromise a DC. One danger is for a person to be physically in the room and touch a DC even without any rights granted to them. Thus, if a person has physical access, he or she owns your computer, since physical access grants them control. Keeping DCs in a secure location is a simple way to ensure Active Direcotry security, but it is often overlooked.

As far as network access is concerned, it is important not to give domain admin privileges to someone who isn't skilled enough to handle the job or to someone you're not sure you can trust. Anyone with the ability to install/modify system files, including services/drivers (such as server operators, backup operators or print operators) owns your computer. There are many ways for this to happen. Naturally, a secure account could be compromised, giving the intruder the rights to do this, but a valid holder of these rights could cause harm unintentionally by installing an application without testing it first.

How well you handle Microsoft patch emergencies and updates is also key to the security of your DCs. You should always deploy the same patches on all domain controllers. DCs should be kept as close to mirror images of each

other as possible, at least in terms of the OS configuration. This will help eliminate incompatibilities, lost or corrupted data and replication errors.

However, it is important not to patch just because Microsoft offers a patch. Every patch needs to be tested in your environment for relevance and reliability. If you don't need it, don't install it. Patches can damage your environment if the install fails to perform perfectly. You don't want to place your DCs at risk if you can avoid it.

Kerberos security with Microsoft

With the inception of Windows 2000, Microsoft adopted Kerberos as an authentication protocol. Not only was it much more secure and efficient than NTLM (which was used prior), but it also plays nicely with other operating systems such as Unix.

Before learning how Kerberos works in the world of Windows, it's best to first understand normal Kerberos authentication and authorization.

Authentication is the process of presenting credentials (username/password) to a service and having that service validate you. It works like this. When a user enters his or her username/password in a Kerberos environment, that information is sent to a server running the Authentication Service. The Authentication Service passes that information to a database called the Key Distribution Center (KDC). If the username/password checks out, the Authentication Service sends a Ticket Granting Ticket (TGT) to the client, allowing the client to complete the logon process. The TGT contains a time stamp, the public key and a certificate.

Authorization is the process of granting access to resources on a server that is in the network. Continuing from the authentication discussion, once the client gets the TGT, the client can then request access to resources. The TGT is presented to the Ticket Granting Service and requests a session ticket to access a resource on, say, Server 1. If Server 1 is in the domain, the Ticket Granting Service sees that there is a valid TGT, so credentials check out, and a session ticket is granted for Server 1. The client then presents the session ticket to Server 1 for access to a resource such as a printer, file share or document. Server 1 will then check access rights on that resource to see what the user can do (read, write, etc.).

In a Windows domain, all of the Kerberos-related services just described are held by each domain controller. When a user presents credentials for authentication in a Windows domain, the same Kerberos authentication process described above is used -- with one exception. In order to find a domain controller that is also the KDC, a client must use the DC Locator process, which requires a DNS server to locate an appropriate DC and send that information back to the client. The client then passes the credentials to the domain controller, which grants the TGT and then a session ticket if the server to be accessed is in the DC's domain. The access rights are checked by the server and granted to the client.

Group Policy security settings

One of the most important steps toward Active Directory security involves Group Policy security settings. With almost 1,800 policy settings in a single Group Policy Object (GPO), it is no wonder they provide so much power, control, security, and management over an Active Directory enterprise.

There are two default GPOs in every Active Directory domain. These default GPOs are there for very distinct reasons and should be investigated to ensure they are configured properly to provide the best security for your company network. The first default GPO is the Default Domain Policy. This GPO is responsible for establishing and maintaining the account policies for the domain user accounts, which are essential for helping secure the domain user account passwords.

The second default GPO is the Default Domain Controller Policy. This GPO is responsible for establishing the baseline security for all domain controllers in the domain. The primary security settings that are established in the GPO are the user rights. Common user rights include:

Allowing a user to logon using the keyboard attached to the computer (locally) Changing the system time Backing up files and folders

Accessing the computer and its resources over a network

However, every network running Active Directory should have more than just the default two GPOs. The reason is that Group Policy provides an automated, centralized method for configuring and deploying security settings to all computers and users within the domain. Some common security related settings and areas of configuration include the ability to restrict which applications can be run on each computer, use IP Security to encrypt data between computers, restrict anonymous connections to computers and audit policy settings per computer.

Remember that there are several network security attacks that can be easily avoided with Group Policy, including simple steps for Kerberos configuration, so be sure to take advantage.

Differences in Active Directory for Windows 2000 and Windows 2003

For the new features and improvements that were built into Windows Server 2003's Active Directory, Microsoft focused on five areas:

1. Integration and productivity2. Performance and scalability

3. Administration and configuration management

4. Group Policy

5. Security

Some changes in the areas of integration and productivity include the abilities to edit multiple Active Directory objects simultaneously, as well as improved interoperability via inetOrgPerson for Novell and Netscape solutions. Replication monitoring was also improved for Windows Server 2003. In particular, a replication enhancement called linked-value replication for objects such as Active Directory group objects was significant, especially for large environments. Linked-value replication solved problems such as inconsistent replication and delays by replicating multi-valued attributes separately.

As far as performance and scalability goes, Microsoft eliminated the need to contact a global catalog (GC) server each time a user logs in. For Windows Server 2003, the GC information is cached at the local domain controller. Other enhancements include support for clustered virtual servers, DC overload prevention and GC replication tuning controls.

For better configuration management, Microsoft added automated DNS zone creation, improved inter-site replication and the ability to rename domains. Better migration and command-line tools were also created for Windows Server 2003 Active Directory. Some of the new command-line tools include:

dsadd -- Allows you to create objects from the command line dsmove -- Moves an object from one OU or container to another within the same domain dsrm -- Will delete an object from Active Directory  dsquery -- Will return an object or list of objects that matches criteria that you specify  dsget -- Will return one or more attributes of a particular Active Directory object

As for Group Policy, Windows Server 2003 greatly improved the Group Policy management interface, which is able to interact with both 2003 and 2000 GPOs. Other improvements included GPO results reports, over 150 new GPO controls and improved client management features. New security features included forest trusts, trusted namespaces, cross-forest authentication and authorization, and a credential manager.

Other changes to Active Directory for Windows Server 2003 include the "Install from Media" option for promoting new domain controllers into a domain, and the Users and Computers MMC snap-in which allows admins to move an object from one location in the directory tree to another more easily.

Active Directory improvements with Windows Server 2003 SP1

Several changes in Windows Server 2003 Service Pack 1 have to do with the way Active Directory handles "tombstoned" objects. Just like in Windows 2000, when you delete an Active Directory object, it is not immediately deleted; instead, it's marked as a tombstoned object. This allows the deletion to be replicated properly to other domain controllers. Once an object has been in this tombstoned state for a certain amount of time, it is finally deleted outright.

In Windows 2000, the default tombstone lifetime was 60 days. However, in Windows Server 2003, Microsoft changed it to 180 days, effectively tripling the amount of time that a deletion had to be communicated to all of the domain controllers in an environment. However, if you have already installed Active Directory using either Windows 2000 or the original Windows Server 2003 media, the default tombstone lifetime will not automatically change when you upgrade to Windows Server 2003 SP1. You will only receive the 180-day tombstone lifetime value automatically by building a pristine 2003 SP1 Active Directory forest.

In addition to modifying the tombstone lifetime for new Active Directory installations, 2003 Service Pack 1 added the SID History attribute to the list of attributes that are retained when an object is tombstoned. When an Active Directory object is tombstoned, it is stripped of most of its attributes, so the tombstoned object only takes up a fraction of the size of the original object within the Active Directory database. Each user, group and computer object within Active Directory is assigned a numeric security identifier, or SID. SIDs are unique within the domain and do not change, even if the security principal is renamed or moved to another container within the same domain.

Prior to Windows Server 2003 SP1, one of the attributes that was stripped when an object was tombstoned was this SID History attribute, which meant that if you restored an object, any previous SIDs that were recorded in its SID History were lost. Fortunately, Windows Server 2003 SP1 includes SID History among the attributes retained when an object is deleted.

Service Pack 1 also made changes in the types of Active Directory information that are logged in the Event Viewer on a domain controller, thus allowing for more proactive monitoring and easier troubleshooting. One such update is Event ID 2089, which is recorded in the Directory Service event log if any directory partition has not been backed up for a significant length of time (half of the tombstone lifetime or more). The event is logged whether the partition is the Schema, Configuration, or domain partitions -- or any application partitions or ADAM partitions that are hosted on the DC in question.

Ever since SP1, administrators can also now run domain controllers using virtualization technology such as Microsoft Virtual Server 2005. That allows you to run multiple domains or forests on a single machine or to use virtualization to reduce the attack footprint of a physical server by separating its roles onto multiple virtual machines.

Changes to Active Directory for Windows Server 2008

Once again, many changes to Active Directory were made with Windows Server 2008. Microsoft has incorporated two very significant features with Windows Server 2008 that will probably relate to most Active Directory deployments: the read-only domain controller (RODC) and server roles.

The read-only domain controller is perhaps the marquee feature for Active Directory in Windows Server 2008. The RODC hosts a read-only copy of the Active Directory database. That is, you can't make any changes to the Active Directory database from a read-only domain controller. You can connect to an RODC to read any information you like (with a few exceptions, which we'll get to in a moment), but you will not be able to perform any write operations without connecting to or being referred to a writeable domain controller.

Also with RODC, the administrator can determine which accounts will be replicated to the domain controller, and replication is unidirectional. RODC doesnot perform any outbound replication. This is a fundamental change from the typical multi-master replication model that many have become familiar with in Active Directory. In Windows 2000 Server and Windows Server 2003, an administrator can connect to any domain controller to make a change, and that change will be replicated out to the rest of Active Directory via outbound replication from the DC that the change originated from.

This is not so with the RODC. The read-only domain controller will receive inbound replication from other writeable Windows Server 2008 DCs, but it will not replicate any information whatsoever out to other DCs. This solves a lot of security issues at remote sites since it will minimize accounts exposed at the site (presumably not any admin

accounts), and anything compromised at the site will not make it out of the site. Combined with the new BitLocker technology, RODC will allow deployment of DCs at smaller sites where it was not feasible before.

Server Core was also developed for Windows Server 2008 as a response to customer requests to provide a lean server operating system that would permit specific server functions to run without all the overhead of the GUI. It has been referred to by Microsoft as a bare bones installation of Windows Server 2008.

With Server Core, after logon, a user will be presented with a desktop with no start menu, taskbar or icons, and two command windows. Installation of roles such as Dynamic Host Configuration Protocol (DHCP), DNS, file services and print server will be done completely from the command line. However, this environment will still allow users to open applications such as Event Viewer, notepad and others. In addition to making the server better defined for administrative purposes and reducing the hardware resources required, Server Core also permits better security at remote sites, allowing a smaller footprint of exposure.

Other changes include the Restartable Active Directory, which allows AD to be restarted without rebooting the server. You can accomplish this via the command line and MMC Snap-ins. It is designed to save admins time on offline operations (like an offline defrag of Active Directory) without taking the server offline and shutting down other services and applications.

The basics of Active Directory planning

When you are performing an Active Directory migration, you basically have two options: domain upgrading or domain restructuring. Domain upgrading is little more than upgrading each existing Windows domain controller to a more current Windows domain controller. The upgrade process starts by upgrading the PDCs in each domain, followed by the BDCs. Domain restructuring involves creating an Active Directory network from scratch. In a restructure, you will move systems and reroute connections to comply with a new infrastructure and layout design. Often restructuring will result in fewer but larger domains.

So the question becomes, "Should you upgrade or restructure?"

Deciding which path to take, or which process to perform first, all depends on your specific situation. But there are a few guidelines that can help you make the choice.

First, if your current domain structure is supporting your work tasks and doesn't seem to involve an inordinate amount of extraneous administration, then upgrading may be preferable. However, if the current domain structure is not adequate and is the primary motivation for the migration, restructuring is likely the way to go. Secondly, if you must support the production environment throughout the migration process, upgrading will retain overall network functionality and therefore is preferable. But if you can afford to lose productivity during the migration, restructuring is better. However, restructuring can be performed on a staggered schedule so no significant loss of productivity is noticed.

Rememeber that while upgrading will cause the least downtime in terms of getting the domain back into working order, it often is an insufficient migration. Many of the benefits of Windows 2000 and Windows 2003-based Active Directory domains cannot be fully realized without reconfiguring the design of your network. Restructuring will require significant work to implement, but it makes reaping the benefits of Active Directory easier to exploit for your organization.

Developing an Active Directory migration strategy

When taking on an Active Directory migration project, like with all large projects, it's best to have a strategy in place. It is key to create an Active Directory migration checklist, with steps such as collecting diagrams and configuration of the current DNS and network structure (bandwidth, remote locations, stability, etc.), determining the rights, objects and policies that will need to be migrated, and creating fall back procedures in case of failure.

Another part of developing your migration strategy, is being aware of the key things you should and should not do when performing an Active Directory migration.

For starters , it's important to make sure that your support staff is brought up to speed before you begin migrating any production system. Depending on the size and structure of your organization, you should have a help desk staff taking support calls. For a complex project like Active Directory, it's a good idea to make a couple of network engineers available as well. Be sure to train all members of the support staff involved in the process. Otherwise, you'll have IT staff fielding questions that they don't know how to answer, and frustration will abound on all sides.

You should also establish a test bed that mimics your production environment as closely as possible in terms of hardware specifications and network speed. Leave nothing to chance in the testing phase. Speaking of testing, be sure to test name resolution and replication before deploying Active Directory in production. Unlike replication under NT4, Active Directory replication is possibly the single most important item required for AD to function correctly. Second only to file replication for a solid Active Directory implementation is name resolution. Whether you are deploying WINS or DNS, ensure that all systems that need to can effectively talk to one another.

Designing Active Directory simply

Active Directory is very flexible. So flexible that you can design an Active Directory forest that is complex beyond imagination. Both Windows 2000 Server and Windows Server 2003 support the Active Directory containers of forest, domain, site, and organizational unit (OU). With the only real restriction of one forest per namespace, you can deploy as many domains, sites, and OUs as you deem necessary.

However, don't be so fast to rush off and design an Active Directory network that includes a domain for every department in your enterprise. The key to Active Directory design is simplicity. As a general rule, you want to keep the number of domains to a minimum whenever possible. If you really need department level divisions on your network that reflect the organization of your business, then use OUs instead. OUs are much more flexible and easier overall to manage than domains.

If you are migrating from a Windows NT 4.0 network to a Windows 2000 Server or Windows Server 2003 Active Directory network, compare the number of domains from your existing legacy system and compare that with the number of domains in your new AD-based design. If your new Active Directory network has more domains than your legacy network, you may need to re-think your design. Yes, it is possible to use as many domains as you wish, but you'll likely regret that decision down the line. If you need lots of groupings and divisions, it is best to rely upon OUs.

Active Directory domain design

When you are designing your Active Directory network, it is important to use the four divisions (forests, domains, organizational units, and sites) to their maximum potential. This is especially true for Active Directory domain design.

Domain divisions are most often used as logical containers. However, Microsoft recommends that you employ domains also as physical containers. In other words, create domains whose members are all geographically close rather than distant. This is an important design aspect since the level of traffic within a domain is considerably higher than that between one domain and another. In general, a domain with limited physical size is less likely to include expensive WAN links or pay-per-bit connections. When slow links must be included in a network design, it is often beneficial to create multiple domains connected by the slower connections.

Remember that it is not necessary to create separate domains to divide administrative privileges. Within Active Directory, it is possible to delegate administrative privileges based on organizational units.

Designing groups and organizational units

With the proper preparation and advance knowledge of their use, a functionalorganizational unit (OU) and group design can do wonders to simplify your Active Directory environment. It can also go a long way toward helping you gain control and reduce overhead.

Often, OUs are indiscriminately used without reason, and group structure is ineffectual and confusing. Without some form of logical organization of users within your network environment, chaos reigns and administration grinds to a halt. Some best practices when designing OUs include:

Keep the OU structure as simple as possible Do not nest OUs more than 10 layers deep  Keep the number of OUs to a minimum Apply Group Policy to groups through Group Policy filtering Don't utilize local groups for permissions in a domain environment Use domain local groups to control access to resources, and use global groups to organize similar groups of users.

You also have the option of hiding your OUs. The primary purpose of hidden OUs is to prevent an administrator from one OU from being able to view, access, or alter another OU. Hidden OUs are often used in environments that offer network application services to internal departments or external customers. It allows for a solid separation of duties without requiring separate domains or forests.

Design rules for Active Directory sites

Sites are an extremely useful design element for Active Directory domains. Sites are limited to any computer object within a forest. Thus, they can cross domains and organizational units (OUs) with indifference. An object's membership in a domain or OU does not exclude simultaneous membership in a site. Sites are used to impose physical network divisions for the purpose of traffic flow.

By using sites, you can control and reduce the amount of traffic that flows over your slower WAN links. This can result in more efficient traffic flow for productivity tasks. It can also serve to keep WAN link costs down on the pay-by-the-bit services.

In general, when designing sites, keep the following in mind:

Sites should generally reflect the physical or geographic topology of the network.  Each site should contain at least one local DC.  Sites should not contain slow links of any type.  Remote-access clients do not need a dedicated site.  Sites should be used whenever control over replication traffic is needed or desired.  Sites can be added, removed, changed, and moved easily without affecting any other AD container configuration.

Active Directory HierarchiesNow that you understand the building blocks of Active Directory, you can start to

understand how to build a hierarchy in Active Directory. One of the foundations of

design for AD has been a flexibility to allow companies to build a structure which fits

into their organization. This flexibility allows organizations of all sizes to use Active

Directory to meet their needs.

Domains and OUs

The most basic design of an Active Directory is a single forest, single domain, no

Organizational Unit design.

Basic AD Installation

For a small organization, this might be adequate, but almost every organization can

benefit from some structure.

Creating multiple domains is not always the best design solution, so Microsoft

created organizational units in Active Directory which can be nested to provide

hierarchical control of your AD environment. It is a great idea to think about and map

out your OU design before committing it into Active Directory.

Typically, companies design their OU trees based on either geographic separation (e.g.

Americas, EMEA, PacificRim) or based on organizational design (e.g. Accounting,

Marketing, Technology, Sales). There is no incorrect way to design your AD

environment, however, consistency should be key. You shouldn’t mix the two design

methods and have a top level Americas OU and a top level Sales OU. Doing so makes

administration difficult as you won’t know where a particular salesperson’s account is.

Also, remember that OUs allow enterprise administrators to delegate administration

responsibility to local teams. Building an effective OU design will allow you to properly

delegate authority.

The other reason OUs are used is to apply policies. Policies are rules for security,

access, and functionality which can apply to several different containers in Active

Directory. Frequently, policies are applied by OU – so though you might separated

geographically (and therefore want to set up your structure based solely on geography),

it might make more sense to setup your AD by organizational divisions. Why? Because if

all of your marketing employees need the same software and settings, you will setup

policies based on the department instead of the physical location of the employees.

Domain Trees

Once an organization becomes large and you cannot have the entire AD database

replicated everywhere, it might make sense to move to a domain tree. A domain tree

allows an organization to become more decentralized as it is more independent than

using an OU tree.

Domain-wide policies can be changed per domain in a domain tree which is not possible

with only an OU structure. Policies such as minimum and maximum password age,

minimum password length, and account lockout are domain-wide policies and cannot be

changed on a per-OU basis. By creating multiple domains, administrators can set these

policies for each domain.

Domain Tree

In the illustration above, learnthat.com has a domain tree in the Active Directory

domain.

Forest of Domain Trees

In more complex environments, a company may use multiple domain trees in a single

forest. This might be a large operating company with multiple subsidiaries – each

requiring their own domain, for example, ThatNetwork.com is the parent company and

subsidiaries might include Learnthat.com, Romancetips.com, Exampractice.com. This

structure makes sense if you have different administrative staff for each domain, along

with different policies and different security requirements.

You can still setup trusts between the domains to allow users to authenticate for

resources in either domain.

Multiple Forests

The last possibility is using multiple forests. This is the less frequent design choice, but

can be used with you want an absolute separation for one reason or another. This

structure is most often found when companies merge or in the case of acquisitions. In

Windows 2003, you can setup forest trusts between forests to allow some access.

Active Directory InstallationSome larger organizations take months (and in some cases, over a year) to plan a

proper Active Directory design and get input from a global organization of technology

leaders. It is extremely important to give a lot of thought to your AD design to ensure it

meets your organization’s needs.

Choosing Your AD LayoutAs we mentioned earlier, there are many ways you can structure your Active Directory.

From a top level down perspective, most companies either start with a geographic

separation or a organizational structure separation, for example Americas, EMEA,

PacificRIM for geographic or Accounting, Marketing, Technology, Sales for organizational

structure. It does not matter which you select: either will provide a fine starting point for

your domain structure, but you need to ensure you pick one direction and be consistent

with your choices.

Many organizations start with geography at the top level, then break down into business

units or departments underneath that top level. It is important to write naming

conventions and standards down so a team in Europe does not call an OU

“SalesMarketing” while a team in North America calls an OU “Sales.” Consistency

provides for an efficient and manageable Active Directory layout.

There are many different combinations you could choose when designing your AD

structure.Installation RequirementsIn this section, we will look at the installation requirements of Active Directory. Installing

AD isn’t a complex process, but the design and configuration can be.

Here are the requirements for installing Active Directory on Windows Server 2003:

An NTFS partition with enough free space

An Administrator's username and password

NIC with Network Connection

Properly configured TCP/IP (IP address, subnet mask and - optional -

default gateway)

An operational DNS server (which can be installed on the DC itself)

A Domain name that you want to use

Windows Server 2003 CD media or the i386 FolderFunctional Levels

In Windows 2000, you chose from two levels: mixed mode or native mode. When

Windows 2000 Server was introduced, NT 4 was still a popular server option. To ensure

backward compatibility with these servers and clients, Windows 2000 defaulted to

mixed mode where you could add Windows NT 4 servers to the Windows 2000 Active

Directory domain.

Windows Server 2003 introduced functional levels - a set level of backward

compatibility for previous operating systems. If you are in an environment with NT 4

servers and Windows 2000 servers which are still accessed, you can set a functional

level to ensure backwards compatibility.

Windows 2003 expands from those two modes to one of many domain functional levels

including Windows 2000 Mixed, Windows 2000 Native, Windows Server 2003 Interim,

and Windows Server 2003. Also, in Windows Server 2003, you have three forest

functional levels available: Windows 2000, Windows Server 2003 Interim, or Windows

server 2003. Each functional level brings new features available and lose compatibility

with some set of servers or clients.

By default, Windows Server 2003 starts at Windows 2000 Mixed functional level. Not all

of the features of 2003 are available in this mode, so if you are designing a new

Windows 2003 AD environment, you will want to take advantage of the new features

added in Windows Server 2003.

In Windows 2000, we referred to this change as “changing the mode,” but in Windows

2003, we now raise the functional level with either Active Directory Users and

Computers or Domains and Trusts.

This change cannot be reversed – once you make a decision to raise the functional

level, you cannot go back to a lower functional level.

Installing Active Directory

Please note: these installation instructions are for a brand new domain – not for adding

a server as a member server or domain controller in an existing domain. Following

these instructions in a production network is not recommended.

We are going to review the AD installation process from a clean install of Windows

Server 2003. You may have already set some of these settings, so look through the

steps and perform any tasks you have failed to do.

Set Network Settings

1.       This server will be both a domain controller and a DNS server, so we are going to

set a static IP address.

2.       Click Start, Control Panel, Network Connections and select your network

connection.

3.       Click Properties.

4.       Click Internet Protocol (TCP/IP) and click Properties.

5.       Enter in your static IP address information and preferred DNS servers. Notice one

of the DNS servers I listed is the server itself – this will be a DNS server in a minute.

6.       Click OK.

7.       Click Close.

8.       Click Close.

9.       Click Start. Right-click on My Computer and select Properties.

10.   Click on the Computer Name tab.

11.   Click on the More button.

12.   Enter in the domain name you are going to be using for your AD domain in

the Primary DNS suffix of this computer text field.

13.   Click OK.

14.   Click OK. Acknowledge that you have to reboot and click OK.

15.   Click Yes to the prompt asking you if you want to reboot.

Install the DNS Service

16.   On the Manage Your Server window, select Add or remove a role. (Don’t see this

window at startup? Find it at Start > All Programs > Administrative Tools >

Manage Server)

17.   Click Next.

18.   Click DNS Server and click Next.

19.   Click Next.

20.   Insert your Windows Server 2003 setup cd and click OK.

21.   Navigate to where the i386 folder is and click OK.

22.   Click Next to start the DNS wizard.

23.   Click Next to create a forward lookup zone.

24.   Click Next that this server retains a the zone.

25.   Name your zone with your domain name. Click Next.

26.   Accept the default filename and click Next.

27.   Click Allow both nonsecure and secure dynamic updates. Click Next.

28.   Select whether or not this DNS server should forward queries. If you use an ISP for

DNS resolution for Internet sites, enter in your ISP’s DNS servers in the first option. If

this DNS server will resolve all queries, select the second option. Click Next.

29.   Click Finish.

30.   Click Finish.

31.   Congratulations! You have setup a DNS server!

Setting Up Active Directory

32.   On the Manage Your Server window, click Add or remove a role.

33.   Click Next.

34.   Select Domain Controller (Active Directory) and click Next.

35.   Click Next.

36.   Click Next when the Active Directory wizard opens.

37.   Click Next.

38.   Click Next.

39.   Click Next.

40.   Enter in your domain name and click Next.

41.   Enter in a NetBIOS name or accept the default and click Next.

42.   Click Next to accept the default locations for the database and log, or select a

location for these files.

43.   Enter a location for the Shared System Volume and click Next.

44.   Click Next.

45.   Click Next.

46.   Enter in a password and click Next.

47.   Click Next.

48.   The wizard will configure Active Directory.

49.   Click Finish to complete the wizard.

50.   Click Restart Now.

Congratulations, you have now completed the Active Directory wizard and AD is

installed.

Creating Organizational Units (OUs)

Creating Organizational Units

As we discussed earlier, Organizational Units provide a mechanism to design a

hierarchical structure within your Active Directory environment. Once you have

designed your AD structure, you are ready to create the OUs in the environment.

1.       Click Start > Administrative Tools > Active Directory Users and

Computers.

2.       Double-click the domain name to open it up.

3.       You will see a default structure with no Organizational Units. Right-click on the

domain nameand select New > Organizational Unit.

4.       Enter the name of the OU you want to create and click OK.

5.       You will now see the OU you just created. Continue the process and build out the

top level OUs.

6.       You now have a structure from which to build your organizational structure. For a

small organization, we would create a Users and Computers organizational unit under

each of the top level OUs.

7.       Right-click on Accounting and select New > Organizational Unit and enter

in Computers. Click OK. Repeat this process for the Users OU.

8.       Now repeat the process for each department and you will have a structure of OUs

created.

Post Active Directory InstallationThere are several steps you should do after the Active Directory installation to ensure

installation went correctly and make sure AD operates properly in your environment.Verify Installation

First, you can ensure the AD tools are installed. Click on Start and

click Administrative Tools. You should have these tools installed:

Next, open Active Directory Sites and Services. You should have a Default-First-

Site-Name listed and when you open it up, you should find your domain controller listed

as a server.

Finally, open up DNS management. Open up the DNS server name, the Forward Lookup

Zones, the domain name, and _tcp. It should look like this with four SRV records:

Once you’ve performed these tasks, you’ve confirmed that your AD environment is

installed.Management Utilities

There are several management utilities you use to manage the Active Directory

environment. As you saw after installation, you have these utilities (which are MMC

snap-ins):

Active Directory Domains and Trusts: Manage domains and trusts between

domains using this tool.

Active Directory Sites and Services: Setup and manage sites (physical networks).

Active Directory Users and Computers: Create and manage users, computers, other

objects, OUs.

In later Active Directory tutorials, you will learn more about these tools and how to use

them.