Group accounts have also changed in Windows 2000. Unlike NT 4 where we only found Global and Local groups, Windows 2000 includes new group types, scopes and abilities. Before we discuss these however, we need to take a look at something referred to as the ‘mode’ of a domain. By default, all domains are created in something called Mixed Mode. In this mode, NT 4 BDCs can still exist, and many of the rules associated with an NT 4 domain still apply. Once all domain controllers have been switched to Windows 2000, the domain can be switched into what is referred to as Native Mode. This is a one-way process. Note that even if you are not upgrading an NT 4 domain, a Windows 2000 domain is still automatically created in Mixed Mode, and the change to Native mode must be made before many of the new feature with respect to users and groups can be used.
Windows 2000 supports two types of groups. The first are very similar to groups in NT 4, and are referred to as Security groups. Quite simply, a security group has a SID, and as such can be part of a Discretionary Access Control List (DACL), the list of users and groups that have permissions to access a resource. The second type of group is called a Distribution group, and exists for the purposes of sending email messages to a group of users. This functionality largely exists for the purpose of Exchange 2000 integration. Distribution groups have no SID, and as such cannot be added to a DACL. You may be asking why it is necessary to make a distinction. The reason relates to what happens when a user logs on – a security token gets created that lists their SID, and the SIDs of the groups they are part of. The larger the number of security groups, the larger the security token for a user, and the longer it will take to log on. Distribution groups provide an easy and less resource-intensive way to be able to integrate messaging technologies with Active Directory.
Every User that needs to log into the domain will require a user account. Note that the account can be created within any container (built-in, or OU that you create), since these are all still technically ‘domain’ accounts. The user will still only need to supply the domain they wish to log into, not the container in which their account actually exists. Unlike NT 4 where the properties relating to a user account were very limited, in Active Directory user account properties are actually quite extensive. Most of these are not configured during the account creation process, but actually afterwards by accessing the properties of an account. Like NT 4, you can change the properties of multiple accounts simulataneously by selecting many accounts and then accessing their properties collectively. The property tabs found on a domain user account differ based on the services installed. For example, if Exchange 2000 is installed, a user’s mail configuration is done from the property sheets. Note that to view some tabs, you must choose Advanced Features from the View menu. The default tabs and their purposes are listed below:
- General – contains basic information about the user including first name, last name, email address, etc.
- Address – home address of the user
- Account – user account details, including logon name, logon hours, account options, and account expiry.
- Profile – user profile and logon script information, as well as home directory details.
- Telephones – various phone numbers for the user.
- Organization – information on title, department, and manager.
- Environment – Terminal services startup information.
- Sessions – settings relating to Terminal service sessions, such as idle session disconnect.
- Remote Control – settings relating to Terminal service remote control options.
- Terminal Services Profile – information relating to Terminal service profile, home directory, and allowing/disallowing logon to terminal server.
- Published Certificates – listing of user’s X.509 certificates and purposes.
- Member Of – listing of groups the user is a member of.
- Dial-in – Dial-in settings for this user, including items such as callback settings.
- Object – shows fully qualified name of the user object, when it was created.
- Security – show access control list associated with this object.
The administration of Active Directory involves the management of domain objects and their associated properties. The objects managed within a domain include user accounts, group accounts, computer accounts, and organizational units primarily. Unlike NT 4 where we used one tool to manage users and groups (User Manager for Domains) and another to manage computer accounts (Server Manager), in a Windows 2000 domain all management of these objects is handled via a tool called Active Directory Users and Computers, an MMC snap-in. Note that this tool can quickly be accessed from the Run command, by running dsa.msc.
When opened, Active Directory Users and Computers will be focused on a particular domain controller. This will be the domain controller to which updates and additions will be written. It can be changed by right-clicking the domain object and choosing to connect to another domain controller instead. This is actually quite useful – because replication between sites can have associated schedules, you might decide to change a user’s properties on their local domain controller instead of another, and thus not have to wait for the changes to replicate. The AD Users and Computers program displays the domain object, and then a series of containers.
First and foremost, the folders that appear beneath the domain object are actually containers. Two types of containers exist – built-in containers, and OUs. A built-in container appears as a plain folder, while an OU looks like a folder with a book icon on it. Note that OUs can have group policies applied to them, while built-in containers cannot. However, both types of container allow you to delegate administrative control. The containers which are created automatically are described below:
- Built-in: This container houses all built-in user and group accounts created when Active Directory is installed.
- Computers: This container houses any upgraded computer accounts, or any new accounts added as part of joining a domain from a client system.
- Domain Controllers: This OU contains all domain controllers for the domain.
- ForeignSecurityPrincipals: Container for SIDs of user accounts from external trusted domains.
- Users: This container is where upgraded user accounts are stored. You will also find the domain Administrator and Guest accounts here.
These are not the only built-in containers that exist, however. If you choose Advanced Features from the View menu, you will also find the following containers:
- LostAndFound: This container houses orphaned objects. For example, imagine if an OU was deleted on one domain controller, and before replication had completed, a user was created in that OU on another domain controller. This user would be placed into the LostAndFound container, since its container object no longer exists.
- System: This container holds settings relating to domain operational information, including AD-integrated DNS, domain DFS configuration, and so forth.
Within these containers (or the root of the domain) other objects can be created such as users, computers, groups and so forth. Note that there is no requirement to actually create users in the Users container, or computer accounts within the Computers container. You can use these, or create additional OUs according to your organizational needs and place accounts there instead. You can also easily move objects between contains by right-clicking the object and choosing Move. To create a new object within a container, right-click the object and choose New, and then choose the appropriate object type you wish to create.
The physical structure of Active Directory relates to two main types of objects – sites and domain controllers.
Unlike NT 4, Windows 2000 Active Directory provides for the concept of physical locations within its design. In Active Directory, a site is a collection of TCP/IP subnets connected at high speed. Though ‘high-speed’ is relative, usually it refers to a collection of subnets connected at LAN-type speeds. You define sites in Active Directory to control replication, authentication, and the location of services. Once sites have been defined, a client computer will attempt to authenticate to a domain controller that is part of the same site, instead of sending the request over the WAN.
Sites also allow you to control when replication can occur between domain controllers. For example, in NT 4, all BDCs replicated with their PDC using a 5-minute interval change notification process. Since there wasn’t any easy way to control replication between physical locations (it was possible by batch scripting to the registry), replication traffic often saturated links and degraded performance. Once you have defined sites in Active Directory, you can also specify the times and days at which replication between sites can occur, how often during these times, and the preferred path that replication should follow. You should note, however, that only one site exists by default, and until you define more sites, replication will continue to occur on the same old 5-minute change notification interval. It is also important to note that sites are another element that allow large companies to have only a single domain – since there is no correlation between the logical and physical structures of Active Directory, you could have one domain and hundred of sites. The ability to control replication traffic is a big part of what makes this more manageable than in the past.
The logical structure of Active Directory will vary based on the needs of an organization. Logical elements include forests, trees, domains, and organizational units.
A domain in Windows 2000 is very similar to what a domain was in NT 4. For all intents and purposes, a domain is still a logical group of users and computers (objects) that forms an administrative and replication boundary. That means two things. First of all, a domain is an administrative unit. As such, an administrator from one domain is only the administrator of that domain, and not necessarily any others. Secondly, all domain controllers in the same domain must replicate with one another. We refer to this as a replication boundary. In Windows 2000, domains are named according to DNS naming conventions, instead of conventions based on Netbios. An example of an Active Directory domain name would be 2000trainers.com. In Windows NT, domains had a restriction on how large they could grow, based on the size of the domain SAM database (40MB or thereabouts). As such it was often necessary to create multiple domains if a company had tens of thousands of users and computers. By comparison, multiple domains wouldn’t actually be required in such a scenario under Windows 2000, since Active Directory can contain literally millions of objects. In the same manner that a user account existed within a domain in Windows NT, the same is true in Windows 2000. A given user should be given only one account, and that account exists within only one domain, even if multiple domains exist. Active Directory does allow you to have multiple domains, forming structures referred to as trees and forests, to be discussed next.
Active Directory is uses the Lightweight Directory Access Protocol (LDAP) as its primary access protocol. LDAP runs over TCP/IP, and defines a way to reference and access objects between an Active Directory client and server. Under LDAP, every object has a distinct Distinguished Name, and this name distinguishes the object from every other object in Active Directory, while also telling us where the object exists. The two main components of a distinguished name are a CN (common name) and a DC (domain component). The common name identifies an object or the container in which it exists, while the domain component references the domains within which the object exists. For example, a distinguished name could be as follows:
CN=Dan DiNicolo, CN=Users, DC = 2000trainers, DC=com
In the above example I have a user called Dan DiNicolo, who exists within a container called Users, in the domain 2000trainers, which is a subdomain of com. The distinguished name of an object must be unique within a given Active Directory forest (more on forests in a bit).
While a distinguished name tells us about the complete context of an object, a relative distinguished name uniquely identifies an object within its parent container. For example, if I were searching within the Users container, the relative distinguished name of the object I identified above would be Dan DiNicolo.
Certainly the biggest single change between Windows NT 4 and Windows 2000 is the inclusion in Windows 2000 of an important new service – Active Directory. Active Directory is the native directory service in Windows 2000. Unlike Windows NT 4, when domains were pretty much stand-alone islands that we connected with trust relationships as necessary,
Active Directory is a full-featured directory service. But what is a directory service? Well, a directory service is actually a combination of two things – a directory, and services that make the directory useful. Simply, a directory is a store of information, similar to other directories, such as a telephone book. A directory can store a variety of useful information relating to users, groups, computers, printers, shared folders, and so forth – we call these objects. A directory also stores information about objects, or properties of objects – we call these attributes. For example, attributes stored in a directory for a particular user object would be the user’s manager, phone numbers, address information, logon name, password, the groups they are a part of, and more.
To make a directory useful, we have services interact with the directory. For example, we can use the directory as a store or information against which users are authenticated, or as the place we query to find information about an object. For example, I could query a directory to show me all the color printers in the Frankfurt office, the phone number of Bob in the Delhi office, or a list all of the users accounts whose first name starts with the letter ‘G’. In Windows 2000, Active Directory is responsible for creating and organizing not only these smaller objects, but also larger objects – like domains, organizational units, and sites. In order to fully comprehend what Active Directory is all about, we need to take an initial look at a number of concepts. A deeper discussion on Active Directory will be covered once we get to the AD Implementation and Administration portion of the series.