Since the basics of this topic have already been covered in previous articles, I will keep this part short. Just as a review, remember that 3 main types of user accounts exist in a Windows 2000 Active Directory environment:
Local User Accounts: These accounts exist in the local Security Accounts Manager (SAM) database on each Windows 2000 system (with the exception of domain controllers). These accounts are created using the Local Users and Groups tool in Computer Management. Note that in order to log on with a local account, the account must exist in the SAM database of the system you are logging in from. This makes local accounts impractical for large environments, due to the administrative overhead involved.
Domain User Accounts: These accounts are stored in Active Directory, and can be used to log on to systems and access resources throughout an AD forest. Accounts are configured centrally using Active Directory Users and Computers.
Built-in Accounts: These accounts are created by the system and cannot be deleted. By default, both standalone systems and domains will have two accounts, Administrator and Guest. The guest account will be disabled by default.
Since this portion of the series covers Active Directory, we will concentrate on domain user accounts. These accounts are stored on domain controllers, which carry a copy of the Active Directory database. You will need to be familiar with the different formats in which user logon names exist, because there are differences to allow for backwards compatibility with ‘downlevel’ clients (such as Windows 95, 98, NT). The two main types of names are the User Principal Name (referred to as the user logon name in the interface) and user logon name (pre-Windows 2000).
A User Principal Name (UPN) is formatted much like an email address. It lists a logon name followed by the ‘@’ sign and domain name. By default, the domain name of the root domain will appear selected in the dropdown box, regardless of the domain in which the account is being created (the drop down list with also contain the domain name of the domain in which you are creating the account). It is also possible to create additional domain suffixes that can appear in the dropdown box and be used in the UPN if you so choose (this is done using Active Directory Domains and Trusts). The only requirement is that all UPNs in the forest be unique. When a user logs on to a Windows 2000 system using a UPN, they need only specify the UPN and the password – there is no longer a need to input or remember the domain name. Another benefit would be having UPNs map to user email addresses, again simplifying the amount of information users need to remember.
The User logon name (pre-Windows 2000) is provided for backwards compatibility with Microsoft systems not running Windows 2000. These systems still rely on traditional Netbios-based authentication, where a username, password, and domain name (in Netbios format) need to be provided. These downlevel logon user names must be unique within a domain. Note that the username portion of both the downlevel logon name and UPN need not be identical.