Creating OUs to Delegate Administration
In versions of Windows NT previous to Windows 2000, delegation of administration within a domain was limited to the use of built-in local groups, such as the Account Administrators group. These groups had predefined capabilities, and in some cases the capabilities did not fit the needs of a particular situation. As a result, there were situations where administrators in an organization needed high levels of administrative access, such as Domain Administrators rights.
In Windows 2000, delegation of administration is more powerful and flexible. This flexibility is achieved through a combination of organizational units, per-attribute access control, and access control inheritance Administration can be delegated arbitrarily by granting a set of users the ability to create specific classes of objects, or modify specific attributes on specific classes of objects.
For example, your human resources department can be granted the ability to create user objects in a particular OU, but nowhere else. Helpdesk technicians can be granted the ability to reset the passwords of users in that OU, but not the ability to create users. Other directory administrators can be granted the ability to modify the address book attributes of a user object, but not be allowed to create users or reset passwords.
Delegating administration in your organization has several benefits. Delegating specific rights enables you to minimize the number of users who must have high levels of access. Accidents or mistakes made by an administrator with restricted capability will only have an impact within their area of responsibility. Previously, in your organization it might have been necessary for groups other than IT to submit change requests to high-level administrators, who would make these changes on their behalf. With delegation of administration, you can push responsibility down to the individual groups in your organization and eliminate the overhead of sending requests to high-level administrative groups.
Modifying Access Control Lists
To delegate administration, grant a group specific rights over an OU. To do this, you need to modify the access control list (ACL) of the OU. The access control entries (ACEs) in the ACL of an object determine who can access that object and what kind of access they have. When an object is created in the directory, a default ACL is applied to it. The default ACL is described in the schema definition of the object class.
ACEs can be inherited by child objects of a container object. If any of the child objects are also containers, the ACEs are applied to the children of those containers as well. With inheritance, you can apply a delegated right to an entire subtree of OUs instead of a single OU. You can also block ACE inheritance on an object to prevent ACEs from a parent container from applying to that object or any child objects. Inheritable ACEs only apply within a domain and do not flow down to child domains.
To delegate control over a set of objects in an OU subtree, you edit the ACL on the OU. The easiest way to do this is by using the Delegation of Control wizard in the Microsoft Management Control (MMC) snap-in for Active Directory Users and Groups. To view the ACL on an object or to perform advanced editing of an ACL, use the Security tab on the property page for the object.
Always reference groups in ACLs, not individual users. Managing the membership of a group is simpler than managing an ACL on an OU. When users change roles, it is much easier to discover and change their group memberships than to check the ACLs on every OU. Where possible, delegate to local groups instead of global or universal groups. Unlike global groups, local groups can have members from any trusted domain, making them better suited for granting resource permissions. Unlike universal groups, local group membership is not replicated to the global catalog, making local groups less resource intensive.
Deciding What OUs to Create
The OU structure that you create will depend entirely on how administration is delegated within your organization. Three ways to delegate administration are:
By physical location. For example, administration for objects in Europe can be handled by an autonomous set of administrators.
By business unit. For example, administration of objects belonging to the Avionics division can be handled by an autonomous set of administrators.
By role or task. This division is according to the type of object being managed. For example, a set of administrators might be responsible only for computer account objects.
These three dimensions are frequently combined. For example, as shown in Figure 9.13, there can be an administrative group that is responsible for computer account objects in Atlanta for the Automotive business unit.
Figure 9.14 Delegating Full Control
If you do not have any units in your organization that need full control, domain administrators will determine the remainder of the OU structure.
Delegating Per-Object Class Control
Groups with full control can decide if additional OUs are necessary to delegate more restrictive control. A simple way to do this is to consider each object class that will be created in the directory, and determine if management of that object class is delegated further in the organization. Although the schema defines many different kinds of object classes, it is only necessary to consider the object classes that your administrators will create in the Active Directory. At minimum, you should consider:
User account objects
Computer account objects
Organizational unit objects
As you examine each object class, separately consider:
Which groups should be granted full control over objects of a particular class? Groups with full control can create and delete objects of the specified class and modify any attribute on objects of the specified class.
Which groups should be allowed to create objects of a particular class? By default, users have full control over objects that they create.
Which groups should only be allowed to modify specific attributes of existing objects of a particular class?
In each case that you decide to delegate control, you will:
Create a local group that will be allowed to perform the specific function.
Grant that group the specific right on the highest OU possible.
To move an object between two OUs, the administrator performing the move must have the ability to create the object in the destination container and to delete the object from the source container. For these reasons, you might want to create a separate group for administrators that can move objects, and grant them the necessary rights on a common parent OU.
The list of objects to be considered can grow as you deploy more Active Directory–aware applications. However, some applications will create objects in the directory that do not require hands-on management. For example, print servers running Windows 2000 automatically publish print queues in the directory. Because the print server takes care of the management of the print queue object, it is not necessary to delegate management to a special administrators group.
By modifying the ACL on the default Computers container, you can delegate the ability to create computer account objects to all users, with no administrative attention required. Computer accounts would be created when users join a computer to a domain in the default Computers container.
Example of Delegating Per-Object Class Control
The Atlanta location for the Automotive unit of the Reskit company is home to two Windows NT 4.0 resource domains, Powertrain and Chassis. Part of the Windows 2000 migration will involve consolidating those two domains into the noam.reskit.com domain.
The Powertrain and Chassis administrators use the domain today to:
Create computer accounts for team members.
Share file system space on Windows NT 4.0 backup domain controllers (BDCs), where access to the file system and shares are controlled by local group membership.
Using delegation of administration, it is simple to replace resource domains with OUs. In this case, groups are created to administer each kind of object, and they are granted full control in a project-specific OU. Project-specific OUs are necessary to prevent Powertrain administrators from being able to manipulate Chassis objects, and vice versa. Figure 9.15 illustrates this concept.
Figure 9.15 Replacing Resource Domains