When planning a network domain migration from Windows NT Server 4.0 to an Active Directory based domain supported by Windows 2000 Server or Windows Server 2003, don't forget to backup. In terms of migration, a backup is a means to return to your pre-upgrade stable-network condition. If things go wrong, you need a means to return the network to a working state.
One straightforward means of domain migration insurance is to make sure you have a fully updated BDC for each PDC in each domain. However, don't stop at just forcing a final full domain replication before starting the PDC system upgrade. There are a few extra steps you need to take. First, be sure every bit of custom data, such as any documents and files created by users, is stored on another system or on a backup media. Next, duplicate the service and network application configuration of the PDC on a BDC. If your PDC is running DNS, then you need to have it installed on your BDC. If your PDC is a print server, DHCP server, WINS server, Terminal Services server, remote access server, or whatever, these exact same services and application should be installed on a BDC. Complete configurations and any data used by these services should be copied onto the BDC as well. Those services and applications installed on the BDC don't need to be activated unless the PDC is destroyed rather than upgraded. Think of the BDC as your PDC-to-be in the event of a catastrophic failure of the PDC during the migration upgrade. One final important step to providing a backup to your domain migration and upgrade process: Take the fully-loaded BDC offline before starting the PDC upgrade process.
And here's an extra step of precaution before you take the BDC offline. You can elect to promote the fully-loaded BDC to a PDC and fully test all of the network services and applications. Then re-promote the original PDC back to PDC status for your upgrade.
James Michael Stewart is a partner and researcher for ITinfopros, a technology-focused writing and training organization.