Designing Migration Paths to Active Directory

When an Active Directory design is in place, you can begin planning the migration. Various migration strategies can be used, depending on the existing network infrastructure. During this phase of Active Directory design, you need to assess the current infrastructure and determine the best way to migrate to Active Directory (more specifically, the best way to migrate to the Active Directory infrastructure that has been designed). Three different migration paths are available:

• In-place upgrade

• Domain restructuring

• New Active Directory environment

In-place Upgrade

With an in-place upgrade, the existing domain infrastructure is maintained. One of the advantages of choosing this migration path is that a business can maintain its current administrative and IT structures. Also, because there is little change, the effect on users is minimized.

Planning for an in-place upgrade includes the following:

• Documenting the existing network infrastructure.

• Determining the order in which domains will be upgraded. User accounts domains should be upgraded first.

• Determining the upgrade paths for the various operating systems. Table 4.1 and Table 4.2 outline the various operating systems that can be upgraded to Windows Server 2003.

Table 4.1. Windows NT 4.0 Supported Upgrade Paths

Operating System	Windows Server 2003 Standard Edition	Windows Server 2003 Enterprise Edition	Windows Server 2003 Datacenter Edition
Windows NT Server 4.0	Yes	Yes	No
Windows NT Server 4.0 Enterprise Edition	No	Yes	No
Windows NT Server 4.0 Terminal Server	Yes	Yes	No

All versions of Windows NT Server 4.0 must be running Service Pack 5 or later before they can be upgraded to Windows Server 2003.

Table 4.2. Windows 2000 Supported Upgrade Paths

Operatin Stystem	Windows Server 2003 Standard Edition	Windows Server 2003 Enterprise Edition	Windows Server 2003 Datacenter Edition
Windows 2000 Professional	No	No	No
Windows 2000 Server	Yes	Yes	No
Windows 2000 Advanced Server	No	Yes	No
Windows 2000 Datacenter Server	No	No	Yes

Domain Restructuring

The difference between an in-place upgrade and domain restructuring is that an in-place upgrade maintains the existing domain infrastructure. In domain restructuring, the existing domain infrastructure is altered to meet the business requirements. For example, existing resource domains might be consolidated into organizational units. One of the benefits of choosing to restructure the existing domain infrastructure is that it provides an opportunity to fix any problems that exist with the current model.

Domain restructuring usually involves migrating user accounts from a Windows NT 4.0 or a Windows 2000 domain to a Windows Server 2003 domain. You can use the Active Directory Migration Tool (ADMT) to migrate objects between domains.

New Active Directory Environment

The third option for migration is to create a new Active Directory environment. You'll need to determine the costs and effects associated with domain restructuring or an in-place upgrade when deciding whether to create a new Active Directory environment. You'll also need to compare the existing domain structure with the new proposed Active Directory infrastructure. Plan to create new Active Directory domains for those domains that cannot be upgraded or restructured.