Before you start implementing a migration from a Windows NT domain to an Active Directory domain (whether based on Windows 2000 Server or Windows Server 2003), you should always fully document your intended domains, forests, organizational units, sites, DNS infrastructure and security strategies. This documentation becomes the plan for your new infrastructure when you make the migration.
When you are performing a migration, you basically have two options: domain upgrading or domain restructuring. Domain upgrading is little more than upgrading each existing Windows NT domain controller to a Windows 2000 or Windows 2003 domain controller. The upgrade process starts by upgrading the PDCs in each domain, followed by the BDCs.
Domain restructuring is 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.
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 2000/2003-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.
When designing a new infrastructure, pay attention to the number of domains in your new design as compared to the number in the previous Windows NT-based design. If your new design incorporates more domains, you should rethink your plans. You may not have taken full advantage of OUs or sites. Active Directory domains can be larger and contain more objects than a Windows NT domain. Plus, fewer larger AD domains are easier to administer than more smaller AD domains.
James Michael Stewart is a partner and researcher for ITinfopros, a technology-focused writing and training organization.