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Managing Domains, Trusts, and DNS

One of the most improved and enhanced features of Windows 2000 is the administrative overhead reduction in terms of domains, trusts, and DNS. In this chapter from Microsoft Active Directory Administration, author Kevin Kocis focuses on these benefits and provides step-by-step examples and exercises.
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In This Chapter

  • Domain Fundamentals

  • Managing Trusts

  • Name Resolution in Active Directory

  • Integrating DNS and Active Directory

  • Heterogeneous Environments

  • DNS and WINS

  • DHCP in Active Directory

One of the most improved and enhanced features of Windows 2000 is the administrative overhead reduction in terms of domains, trusts, and DNS. This chapter focuses on those benefits as well as step-by-step examples and exercises.

Domain Fundamentals

Windows 2000 domains and Active Directory depend on one another and even are defined by each other's characteristics. Let's start with an explanation of the Windows 2000 domain model and examine why that model is so different from the Windows NT domain model.

As you'll recall, Windows NT 4.0 domains didn't scale well. Using one-way non-transitive trusts in enterprise implementations required significant administrative overhead. Windows 2000 has a new approach to trusts and is now in coordination with industry standards such as the Lightweight Directory Access Protocol (LDAP) and Domain Name Service (DNS).

As you learned in Chapter 1, "Understanding Active Directory," Windows 2000 domains are organized in a hierarchy (including trees and forests), as opposed to manually trusted, non- contiguous domain namespaces. The first domain created in a Windows 2000 deployment is called the root domain. This domain serves as the root for all domain trees created in the forest. Each domain tree has its respective subroot. Because Windows 2000 domain structures share a direct relationship with DNS domain hierarchies, the structure of Windows 2000 domains is similar to the familiar structure of DNS domain hierarchies. Examples of root domains are kevinkocis.com or north-rim.com. They serve as the roots of their DNS hierarchies and roots of their respective Windows 2000 domain structure.

Domains subsequently created in a given Windows 2000 domain hierarchy become child domains of the root domain. For example, if sales is a child domain of north-rim.com, the sales domain becomes sales.north-rim.com.

Windows 2000 requires that domains be either a root domain or a child domain in a domain hierarchy, and must be unique in respect to their parent domain. Refer to Figure 2.3 in Chapter 2, "Active Directory Architecture," for a visual guide.

Note - You cannot have two domains called sales that are direct child domains of a root domain called north-rim.com, for example. However, you can have two domains called sales in the overall domain hierarchy. You could have sales.north-rim.com as well as sales.az.north-rim.com.

Because the Windows 2000 domain is an administrative boundary, administrative privileges do not flow across domain boundaries or down through a Windows 2000 domain tree. For example, in Figure 3.1, kevinkocis.com is the root domain and the parent domain of na.kevinkocis.com, and na.kevinkocis.com acts as the parent domain of il.na.kevinkocis.com. Users with administrative rights in domain kevinkocis.com do not have administrative rights in na.kevinkocis.com, nor do users with administrative rights in na.kevinkocis.com have administrative rights in domain il.na.kevinkocis.com. Only Enterprise Administrators, located in the root domain, had administrative powers over the entire forest. They can delegate authority to domain administrators to have administrative authority over a remote domain.

Figure 3.1
A domain tree.

Managing Domains

The Microsoft Windows 2000 domain structure and its associated objects have changed significantly from their Windows NT 4.0 incarnations. Two significant changes are the domain scalability and the transition to a two-way transitive trust relationship mode.

Windows 2000 is more scalable than Windows NT 4.0. Windows NT 4.0 has a limit of 40,000 user accounts in a single domain. This limit comes from the maximum recommended size of the Security Accounts Manager (SAM) database file of 40 MB. Based on this, organizations were forced to create additional account domains to be able to support the number of user accounts expected in the organization. Another reason for creating additional domains was for administrative delegation. Because the domain is the most granular administrative unit, creating additional domains was one way to delegate administrative roles. Business groups also forced enterprises to allow them to create additional domains that were—outside of political realms—unnecessary.

With a Windows 2000 Active Directory implementation, organizations should avoid creating additional domains. Windows 2000 supports significantly larger numbers of objects in its database. Within a domain, organizational units are used to create very granular administrative roles. Therefore, very large organizations do not need to create additional domains to support their large user account requirements. You can implement a strong organizational unit (OU) model as opposed to multiple domains.

The main recommendation for planning domains and DNS is to delegate a separate DNS zone per each Active Directory domain—in other words, mirroring the AD structure. You should have two DNS servers running on domain controllers in the domain. Remember that when a domain is implemented, you cannot change its name or split it into two domains. You also cannot combine two domains. However, you can use an import/export tool called ldifde.exe to transport objects outside the forest. For object transfers within the forest but between domains, use the movetree.exe tool. Both tools are covered in more detail in Appendix A.

In Windows NT 4.0, all trusts were configured via one-way, non-transitive trusts. To establish a two-way trust, administrators from the two domains were required to coordinate two separate one-way trusts. These trusts were also non-transitive.

In Windows 2000, all trusts are two-way, transitive trusts. The exceptions are explained in Chapters 1 and 2. This enhancement eliminates administrative overhead in terms of trust configuration and management.

Adding Domains

Basing domain creation on stable criteria such as geography is the best way to ensure migration will be as simple as possible. Other criteria, such as business groups or suborganizations, are much less stable and are likely to result in the need to move security principal accounts between domains.

You can migrate Windows NT 4.0 domains to Windows 2000 domains in one of the following ways:

  • Create a new Windows 2000 domain and join an existing tree.

  • Create a new Windows 2000 domain and create a new tree.

  • Merge into an existing Windows 2000 domain.

Note - You cannot move the security principals from a Windows NT 4.0 domain into more than one Windows 2000 domain at upgrade time. You need to use the Active Directory Services Interface (ADSI) and other tools to move the user accounts between domains after the upgrade is completed.

Domain Models

The two domain modes are mixed mode and native mode. Mixed mode is the default mode setting for domains on Windows 2000 domain controllers. Mixed mode allows Windows 2000 domain controllers and Windows NT backup domain controllers to cohabitate in a domain. Mixed mode does not support the universal and nested group enhancements of Windows 2000.

You can change the domain mode setting to Windows 2000 native mode only after all Windows NT domain controllers are either removed from the domain or upgraded to Windows 2000. After that, if you do not plan to add any more down-level domain controllers to the domain, you can switch the domain from mixed mode to native mode. Also, native mode does not support down-level replication.

Several things happen during the conversion from mixed mode to native mode:

  • Support for down-level replication and down-level domain controllers stops.

  • You can no longer add new down-level domain controllers to the domain.

  • All domain controllers are equal, even the Primary Domain Controller (PDC) during the migration process.

Caution - Do not change the domain mode if you have or will have any Windows NT 4.0 domain controllers! The change from mixed mode to native mode is one way only. You cannot change from native mode to mixed mode.

Changing Domain Mode

To switch the domain mode, perform the following:

  1. Start the Active Directory Users and Computers snap-in or the Active Directory Domains and Trusts snap-in.

  2. Right-click the domain name, and then click Properties.

  3. On the General tab, click Change To Native Mode.

  4. In the Warning dialog box, click Yes and then click OK.

Note - It may take up to 15 minutes for a domain mode change to impact all Windows 2000 domain controllers.

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