Managing the Directory
4.1: Overview of Managing the Directory
DNS and Active Directory
The designers of Windows 2000 chose the Internet Engineering Task Force (IETF) standard Domain Name System as the name resolution service to support the Active Directory. The IETF documents its standards in Requests for Comments (RFC). The fundamental specifications describing the fundamentals of DNS and DNS naming are described in the following RFCs:
1034 Domain NamesConcepts and Facilities
1035 Domain NamesImplementation and Specification
1123 Requirements for Internet HostsApplication and Support
2181 Clarifications to the DNS Specification
In addition, Active Directory requires that the DNS service support RFC 2052, a DNS RR for specifying the location of services (DNS SRV). And the DNS server should support RFC 2136, Dynamic Updates in the Domain Name System (DNS UPDATE).
The full text of these RFCs plus others that describe different aspects of DNS, including dynamic updates and replication, can be found at the IETF Web site (http://www.ietf.org/). See the Windows 2000 Server Help for the specific DNS RFCs and Internet Draft RFCs that are supported.
Both the Active Directory namespace and the DNS namespace are very similar in design. They both follow the basic rules that each child can have only one parent and each parent can have only one child with any given name. It is important to note that every Windows 2000 domain must have a corresponding DNS domain.
Due to the Active Directory's heavy reliance on DNS, Windows 2000 Domain Controllers register several records in the DNS database. Specifically, Windows 2000 registers SRV records for Domain Controllers, Global Catalog servers, Kerberos Key Distribution Centers, Kerberos Password Change servers, and others. In addition to these records, Windows 2000 also registers SRV records, based on Windows 2000 sites, to simplify clients finding services within a site.
The DNS service that is included with Windows 2000 is the best choice for supporting the Active Directory, although third-party DNS servers can function acceptably (for example, later versions of BIND). Windows 2000 DNS has several features that are attractive to DNS administrators, such as the capability to store DNS information in the Active Directory, support for multi-master updates of DNS zones, methods for aging and scavenging records, and a process to secure DNS records using Access Control Lists (ACLs). However, you can still use third-party DNS services to support the Active Directory as long as they support the Service Locator (SRV) record as described in RFC 2052.
Configuring a Domain Controller
Domains and Domain Controllers in Windows 2000 are very different from what they were in Windows NT 4.0. In Windows NT, Domain Controllers knew only about the objects in their Domain. However, Windows 2000 Domain Controllers have three naming contexts: the Domain, the Schema, and the Configuration. The Domain context is the set of all objects and attributes in the Domain. For example, this includes users, groups, and computers. The Schema context is the knowledge of the objects (or classes) and attributes that exist for the entire forest. Finally, the Configuration context includes information on such objects as replication, the Active Directory namespace, and sites.
Domains in Windows 2000 are part of a hierarchical namespace. These Domains are connected to their parent and children Domains with two-way Kerberos transitive trusts. It is no longer necessary to maintain manually a complex web of one-way trust relationships.
However, setting up a Domain requires a lot more planning than in previous versions of Windows NT. You must plan in advance how all of the domains fit together in the hierarchical namespace and then build your forest starting with the root. You cannot build a Domain until its immediate parent exists, for example.
When setting up a Domain Controller, you need to know how that DC fits into your Domain plan. You need to decide if that DC will be a new Windows 2000 forest, a new tree within an existing forest, or a replica DC in a Domain that already exists.
Installing a Domain Controller is no longer an activity that occurs during the operating system's installation. In order to configure a server as a Domain Controller, you must run the Active Directory Wizard (DCPROMO) after the server is up and running. Also a very nice feature is the capability to remove the Active Directory (server would no longer be a Domain Controller) without reinstalling the Operating System.
Finally, if classes of objects or attributes do not exist, it is possible to extend the Active Directory schema. By using the Active Directory Schema MMC snap-in, a privileged user can add attributes to existing classes or even add new classes. This can allow an administrator to create new object types, either from scratch or derived from some other class. Active Directory-based applications or administrator written scripts can then make use of these new classes or attributes.
Extreme caution should be used in extending the Schema because classes and attributes cannot be removed; they can only be disabled. For the most part, this is not a major risk. But because the Schema is forest-wide, choosing names badly could, in extreme circumstances, affect applications from being installed in the future. Careful planning can reduce the risks.
Creating and Managing User Accounts
User creation and management in Windows 2000 is accomplished through the use of the Active Directory Users and Computers MMC snap-in. It is also possible to automate the creation and management of user accounts through the use of Active Directory Services Interface (ADSI) and Windows Scripting Host. ADSI can be used in scripting languages such as VB script or Java Script, or in full programming languages such as Visual Basic or Visual C++. The Resource Kit has a number of ADSI script samples that you can both use and adapt.
Creating a user account is usually done through the MMC snap-in. This populates only a very basic subset of attributes with data. However, after creating the account, you can edit its properties to add data to other attributes. You can also create a user account using an ADSI script.
Because Windows 2000 is a directory of data, not just an account database, there is a lot more useful information available that applications and users can take advantage of. User accounts in Windows 2000 have many more properties than in Windows NT. These properties allow you to store information about the user in the Active Directory. Some of these properties include telephone number, employee number, address, and department number. Through the Managed by property, you have the ability to link managers to employees. This allows you to build a representation of your company's organizational chart in the Active Directory.
Creating and Managing Groups
Group creation and management in Windows 2000 is also usually accomplished through the use of the Active Directory Users and Computers MMC snap-in. As in Windows NT 4.0, with the MMC tool it is possible to both select the group and add members, or to select the user and add group membership. Through the use of ADSI, it is also possible to automate group management as for user accounts.
Windows 2000 expands the types of groups available to manage your environment, providing you with several more options than just simply Global and Local groups. Windows 2000 introduces a new type of group called Universal groups. Universal groups can contain users, Global groups, or other Universal groups from anywhere in your forest. Although Universal groups are very powerful, they exist only if the domain is in Native mode. Universal groups and their memberships are stored in the Global Catalog. Also, the behavior of Domain Local groups has been modified. In Windows 2000, Domain Local groups can contain users and Global groups from anywhere in the forest. However, they can also contain other Domain Local groups within their Domain. Once created, these Domain Local groups can be tied to ACLs or privileges on member servers and workstations within the domain.
Windows 2000 Domains operate in one of two modes: Mixed mode or Native mode. In Mixed mode, both Windows NT 4.0 and Windows 2000 Domain Controllers can be used. With Mixed mode, you can always migrate back to a Windows NT 4.0 Domain. Once you go Native, there is no way back, but you do gain a number of cool features, including group nesting, Universal groups, and the ability to use the Domain restructuring tools in the Resource Kit, such as ClonePrincipal.
Windows 2000 also allows two classifications of groups: Security groups and Distribution groups. Security groups are used to control access to resources. These are the same types of groups that exist in Windows NT. Distribution groups are a new classification of group in Windows 2000. Distribution groups will be used by Exchange 2000, which will integrate with the Active Directory. Distribution groups are used to send e-mail.
Logging On and Authentication
Almost everything is different in Windows 2000, and the logon and authentication process is no exception. The Windows 2000 default authentication package is Kerberos, although Windows 2000 Domain Controllers also implement NT 4.0-style authentication for support of down-level clients. Kerberos is an industry standard that was developed at Massachusetts Institute of Technology (MIT).
Under Kerberos, when a user is authenticated, they are given a Ticket Granting Ticket (TGT). The TGT allows the user to get another type of ticket that is required to connect to a resource. These other tickets are called Session Tickets. When a user that has been granted a TGT needs to connect to a resource, that user contacts the Key Distribution Center (KDC) in order to get a Session Ticket for that resource. The user then presents that Session Ticket to the resource. The resource mutually authenticates the Session Ticket and allows the user access. By default, tickets in Windows 2000 are good for 10 hours. After that, they are invalid and need to be reissued. Windows 2000 handles this transparently for the user.
You can use Group Policies to change the defaults for the maximum ticket life for both user and service tickets. When you create a Domain, dcpromo also creates a default Domain policy that defines these and other Kerberos settings.
Your user token in Windows 2000 is slightly expanded from Windows NT 4.0. The Windows 2000 token contains your primary SID, the SIDs in your SIDHistory, the SIDs of any Universal groups that you belong to, and the SIDs of all Domain Global and Local groups. Because SIDHistory and Universal groups depend on the Global Catalog, they are available only in Native mode.
Of course, Windows 2000 also supports LAN Manager authentication as a fallback. This allows Windows 2000 to interoperate with Windows 95, Windows 98, and Windows NT.