Microsoft Active Directory provides the structure to centralize the network management and store information about network resources across the entire domain. Active Directory uses Domain Controllers to keep this centralized storage available to network users. In order to configure a Windows Server 2008 machine to act as Domain Controller, several considerations and prerequisites should be taken into account, and several steps should be performed. In this article I will guide you through these prerequisites and steps of creating a new Windows Server 2008 Domain Controller for a new Active Directory domain in a new forest.

Considerations when Installing a new Windows Server 2008 forest

When you install AD to create the first domain controller in a new Windows Server 2008 forest, you must keep the following considerations in mind:

You must make forest and domain functional level decisions that determine whether your forest and domain can contain domain controllers that run Windows 2000 Server, Windows Server 2003, or both. To read more about forest and domain functional levels please refer to the links below.
Domain controllers running the Microsoft Windows NT Server 4.0 operating system are NOT supported with Windows Server 2008.
Servers running Windows NT Server 4.0 are NOT supported by domain controllers that are running Windows Server 2008, meaning you MUST have additional DCs running Windows 2000/2003 to support older NT 4.0 servers.
The first Windows Server 2008 domain controller in a forest must be a global catalog server and it cannot be an RODC.

Considerations when Installing a new Windows Server 2008 domain in an existing Windows 2000/2003 forest

When you install AD to create the first domain controller in a new Windows Server 2008 domain, you must keep the following considerations in mind:

Before you create a new Windows Server 2008 domain in a Windows 2000/2003 forest, you must prepare the forest for Windows Server 2008 by extending the schema (that is, by running ADPREP /forestprep).
You must make domain functional level decisions that determine whether your domain can contain domain controllers that run Windows 2000 Server, Windows Server 2003, or both. To read more about forest and domain functional levels please refer to the links below.
I recommend that you host the PDC emulator operations master role in the forest root domain on a domain controller that runs Windows Server 2008.

General considerations

Make sure you read and follow the requirements described in my "Active Directory on Windows Server 2008 Requirements" article.

Installing Active Directory Domain Services (AD-DS)

In Windows Server 2008, unlike previous server operating Systems, there is an additional step that needs to be taken before running DCPROMO to promote the server to Domain Controller and installing Active Directory on it. This step is the installation of Active Directory Domain Services (AD-DS) role on the server. In fact, the AD-DS role is what enables the server to act as a Domain Controller, but you will still need to run DCPROMO the regular way.

AD-DS can be installed in one of 3 methods:

Method 1 – Server Manager/Initial Configuration Tasks

Roles can and should be added from Server Manager (but they can also be initiated from the Initial Configuration Tasks wizard that auto-opens the first time you log on to the server).

Open Server Manager by clicking the icon in the Quick Launch toolbar, or from the Administrative Tools folder.

Wait till it finishes loading, then click on Roles > Add Roles link.

In the Select Server Roles window, click to select Active Directory Domain Services, and then click Next.

In the Active Directory Domain Services window read the provided information if you want to, and then click Next.

In the Confirm Installation Selections, read the provided information if you want to, and then click Next.

Wait till the process completes.

When it ends, you can click to Close this window, or select the "Close this window and Launch Active Directory Domain Service Installation Wizard (dcpromo.exe)" as shown.

NOTE: If you close this window without selecting that option, you can still run dcpromo.exe

To run DCPROMO, enter the command in the Run command, or click on the DCPROMO link from Server Manager > Roles > Active Directory Domain Services.

Depending upon the question if AD-DS was previously installed or not, the Active Directory Domain Services Installation Wizard will appear immediately or after a short while. Click Next.

In the Operating System Compatibility window, read the provided information and click Next.

In the Choosing Deployment Configuration window, click on "Create a new domain in a new forest" and click Next.

Enter an appropriate name for the new domain. Make sure you pick the right domain name, as renaming domains is a task you will not wish to perform on a daily basis. Click Next.

NOTE: Do NOT use single label domain names such as "mydomain" or similar. You MUST pick a full domain name such as "mydomain.local" or "mydomain.com" and so on.

The wizard will perform checks to see if the domain name is not already in use on the local network.

Pick the right forest function level. Windows 2000 mode is the default, and it allows the addition of Windows 2000, Windows Server 2003 and Windows Server 2008 Domain Controllers to the forest you're creating.

Pick the right domain function level. Windows 2000 Native mode is the default, and it allows the addition of Windows 2000, Windows Server 2003 and Windows Server 2008 Domain Controllers to the domain you're creating.

NOTE: If you select "Windows Server 2008" for the forest function level, you will Not be prompted to pick a domain function level.

The wizard will perform checks to see if DNS is properly configured on the local network. In this case, no DNS server has been configured, therefore, the wizard will offer to automatically install DNS on this server.

Note: The first DCs must also be a Global Catalog. Also, the first DCs in a forest cannot be a Read Only Domain controller.

NOTE: It's most likely that you'll get a warning telling you that the server has one or more dynamic IP Addresses. Running IPCONFIG /all will show that this is not the case, because as you can clearly see, I have given the server a static IP Address. So, where did this come from? The answer is IPv6. I did not manually configure the IPv6 Address, hence the warning. In a network where IPv6 is not used, you can safely ignore this warning.

You'll probably get a warning about DNS delegation. Since no DNS has been configured yet, you can ignore the message and click Yes.

Next, change the paths for the AD database, log files and SYSVOL folder. For large deployments, carefully plan your DC configuration to get the maximum performance. When satisfied, click Next.

Enter the password for the Active Directory Recovery Mode. This password must be kept confidential, and because it stays constant while regular domain user passwords expire (based upon the password policy configured for the domain, the default is 42 days), it does not.

This password should be complex and at least 7 characters long. I strongly suggest that you do NOT use the regular administrator's password, and that you write it down and securely store it. Click Next.