You should be familiar with the process of upgrading a domain from Windows NT 4 to Windows 2000 for the Server portion of exam. Creating your new Active Directory domain involves upgrading your existing domain controllers to Windows 2000. Note that member servers and workstations can be upgrading at any time, whether before or after the domain upgrade takes place.
When upgrading a domain, the first machine to be upgraded should be the current PDC. Upgrading the domain will allow all user, group, and computer information that currently exists to be migrated to Active Directory. Before you upgrade the PDC however, Microsoft recommends that you do a full domain synchronization, and then take one BDC offline. If the upgrade were to fail, you could then place the BDC back on the network, promote it to the PDC, and be back to where you originally started.
After you upgrade the PDC and get Windows 2000 installed, dcpromo will run automatically to turn the system into a domain controller. Your domain will now be in something referred to as Mixed mode, or a state where NT 4 BDCs can continue to exist, using the upgraded PDC (who is now the PDC emulator) as their domain synchronization source. Once all domain controllers have been upgraded to Windows 2000, you can switch the domain to Native mode. The differences between Mixed and Native mode are discussed below:
Mixed Mode: A mode that allows for NT BDC to continue to exists, and allows you to revert to an NT 4 domain if necessary. Even in a non-upgrade scenario, Windows 2000 automatically creates new domains in Mixed mode, requiring you to explicitly switch the domain to Native mode.
Native Mode: In Native mode, all domain controllers run Windows 2000. The switch to native mode provides the ability to create Universal groups, nest groups, and control remote access via RAS policy amongst other things.
Note that changing from Mixed mode to Native mode is a one-way process and cannot be reversed. Some possible problems / issues with respect to upgrading domains that you should be aware of:
- All domain controllers running Windows 2000 require at least one NTFS partition to house the SYSVOL folder. This is the folder structure that needs to be replicated amongst domain controllers.
- A system being upgraded must be configured to use a DNS server that supports SRV (service) records.
- If no DNS server is available, Windows 2000 will create one for you, making the system an Active Directory Integrated DNS server (more on this later in the series).
- If the dcpromo process fails or returns an error, ensure that domain names provided are entered correctly, that proper network connectivity exists, and that there is enough disk space (dcpromo requires approximately 250 MB of space total).