Understanding and Implementing Policy
Configuring a particular system and the environment for a particular user begins with its defaultsthe settings determined by Microsoft during the development of Windows 2000. Of course, there are numerous settings for which Microsoft's defaults are not appropriate for one or more computers or users. Therefore, users and administrators often find themselves modifying the defaults.
In the past, if several settings needed to be changed, you often had to use several tools, including User Manager, Server Manager, System Policy Editor, and even Registry Editor. If settings needed to be changed on multiple computers, it was often necessary to make those changes on each system individually. And if a setting you specified was later changed inappropriately, there was often no way to set it back to the desired setting except by manually making the change again.
Managing changes and configuration has been significantly improved in Windows 2000, thanks to the introduction into the Windows environment of policy-based administration. Policies provide administrators with a single list of configuration settings in one tool, rather than many tools, and allow administrators to apply those configuration settings to one machine, many machines, or every machine.
On a Windows 2000 Professional system, you can configure security-related settings by using the Local Security Settings console, which contains the Security Settings Microsoft Management Console (MMC) snap-in. To open this snap-in, you simply choose Start, Settings, Control Panel, Administrative Tools, Local Security Settings. Each of the nodes in the Local Security Settings console is a security area or scope within which you will find dozens of security related settings (also called attributes).
The Local Setting column of the details pane displays the settings as specified by the local policy. The Effective Settings column shows what is currently in effect. The two columns may differ if the local policy has not been implemented; changes to security settings take effect when the system is restarted or following a refresh interval, which is by default 90 minutes. The columns may also differ because local policy settings are overridden by group policy settings, which is discussed later in this chapter.
Local policy settings include user rights assignments such as the ability of certain users to log on locally to the computer. You can use local policy to enable auditing for various types of events, such as which users are successfully or unsuccessfully logging on to the computer. You can use local policy to configure several different security options, such as whether to have Windows 2000 display the username of the last logged-on user in the Log On to Windows dialog box. Local policy also provides account policy settings for users that allow you to specify password requirements, among other things.
Account policies control the password requirements and how the system responds to invalid logon attempts. The policies you can specify include the following:
Maximum password ageThis is the period of time after which a password must be changed.
Minimum password lengthThis is the number of characters in a password. Passwords can contain up to 127 characters; however, most passwords should not exceed 14.
Passwords must meet complexity requirementsThis policy, if in effect, does not allow a password change unless the new password contains at least three of four character types: uppercase (A through Z), lowercase (a through z), numeric (0 through 9), and nonalphanumeric (such as !).
Enforce password historyThis policy specifies the number of previous passwords that the system can remember. When a user attempts to change his or her password, the new password is compared against the history; if the new password is unique, the change is allowed.
Minimum password ageThis specifies the number of days that a new password must be used before it can be changed again.
Account lockout thresholdThis is the number of denied logon attempts after which an account is locked out. For example, if this policy is set to three, a lockout occurs if a user enters the wrong password three times; any further logon attempts are denied. If this policy is set to zero, there is no lockout threshold.
Reset account lockout counter afterThis is the number of minutes after which the counter, which applies to the lockout threshold, is reset. For example, if the counter is reset after five minutes and the account lockout threshold is three, a user can log on twice with the incorrect password. After five minutes, the counter is reset, so the user can log on twice more. A third invalid logon during a five-minute period locks out the account.
Account lockout durationThis specifies how long logon attempts are denied after a lockout. During this period, a logon with the locked out username is not authenticated.
Audit policies specify what types of events are entered into the security log. The following are the most important policies to understand:
Logon eventsThis policy deals with authentication of users logging on or off locally and making connections to the computer from remote systems.
Account managementThis policy deals with any change to account properties, including password changes and the addition, deletion, or modification of users or groups.
Object accessThis policy deals with access to objects on which auditing has been specified. Auditing object access, for example, enables auditing of files and folders on an NT File System (NTFS) volume, but you must also configure auditing on those files and folders. See Chapter 2, "Implementing and Administering Resources," for a detailed discussion of auditing.
Privilege useThis policy deals with use of any user right, called a privilege. For example, this policy audits a user who changes the system time because changing system time is a privilege.
For each policy, you can specify to audit successes, failures, or both. As events are logged, they appear in the security log, which can be viewed, by default, only by administrators. Other logs can be viewed by anyone.
User Rights Assignment
User rights, also called privileges, allow a user or group to perform system functions such as change the system time, back up or restore files, and format a disk volume. Some rights are assigned to built-in groups. For example, the Administrators group can format a disk volume. You cannot deny that right to members of the Administrators group, nor can you assign that right to a user or group you create. Other rights are assignable. For example, the right to back up files and folders is given by default to the Administrators group and the Backup Operators group, but you can remove the right for those groups or assign the right to other users or groups. You can modify the rights that are displayed in the Local Security Settings console. Other built-in rights that are not displayed in this console are not modifiable.
User rights, because they are system oriented, override object permissions when the two are in conflict with each other. For example, a user may be denied permission to read a folder on a disk volume. However, if the user has been given the privilege to back up files and folders, a backup of the folder succeeds, even though the user cannot actually read the folder.
The Security Options node contains a number of useful security settings. This node highlights one of the advantages of using (local or group) policy settings: Although many of these settings are accessible elsewhere in the user interface (for example, you can specify driver signing in the System applet), policy settings allow you to compile all those settings, from all those tools and applets, into a unified configuration tool.
Some particularly useful options to be familiar with are the following:
Disable Ctrl+Alt+Delete requirement for logonIf this policy is enabled, the logon dialog box does not appear at startup, and the system boots directly to the desktop. This policy is enabled by default on standalone systems and disabled by default when a machine joins a domain, due to the obvious security implications of bypassing a secure logon.
Clear the Virtual Memory Pagefile when the system shuts downWith this policy, by default, the pagefile is not cleared and could allow unauthorized access to sensitive information that remains in the pagefile.
Do not display last username in logon screenThis policy forces users to enter both usernames and passwords at logon. By default, this policy is disabled, which means the name of the previously logged-on user is displayed.
Managing Local Policies
The Local Security Settings console is most helpful on standalone systems. The local policy sets the configuration of the computer, and if a setting is changed through tools other than the Local Security Settings console, the change is reverted to the policy-specified setting when the system is restarted or following the policy refresh interval.
It is possible, however, to transfer security policies between systems. If you right-click the Security Settings node, you can export and import policies. This allows you to copy a policy you have created on one machine to other machines. However, you can imagine the complexity of trying to maintain consistent local policies across multiple systems. That complexity is addressed by group policy, which is discussed in the following section.
The Security Configuration and Analysis snap-in allows you to capture the security configuration of a system as a database and to use that database as a baseline against which you can gauge changes to security settings. When modifications are made that deviate from the database setting, you can reapply the original setting. You can also save the database as a template, which you can then apply to other systems to duplicate security settings. There are also preconfigured security templates that you can apply to Windows 2000 systems to implement a variety of security environments.
Group policy (technically referred to as GPOs)applies the concept of policy-enforced configuration to one or more computers with one or more users. Similar to local policy, group policy provides Active Directory administrators with a centralized group of configuration settings that get inherited from a parent container, such as a domain, to child containers, such as OUs, that are stored within the domain. You can apply, or link, a group policy to the following:
A domainThis causes the configuration specified by the policy to be applied to every user or computer within the domain.
An OUThis applies group policy settings to users or computers within the OU.
A siteThis is an Active Directory object that represents a portion of your network topology with good connectivity (such as a local area network [LAN]).
To access group policy, you must go to the properties of a site, domain, or OU (SDOU) and click the Group Policy tab. Therefore, to work with group policy for a site, you use the Active Directory Sites and Services console, right-click on a site, and choose Properties. To work with group policy for a domain or an OU, you use the Active Directory Users and Computers console, right-click a domain or an OU, and choose Properties.
Whereas an individual machine can have only one local policy, an SDOU can have multiple policies. On the Group Policy properties sheet, you can create a new GPO by clicking New or you can link an existing group policy to the SDOU by clicking Add. If you select a group policy and click Edit, you expose the GPO in the Group Policy Editor.
The terms group policy and GPOs are routinely used interchangeably. Whenever you hear or see references made to group policy in relation to Active Directory, rest assured that, technically, GPOs are being discussed.
Application of Group Policy
Group policy (or GPOs) are divided into the Computer Settings and User Settings nodes. The computer settings apply to every computer in the SDOU to which the policy is linked and, by default, to all child OUs. Computer settings take effect at startup and every refresh interval (which is by default 90 minutes). User settings affect every user in the SDOU and its children at logon, and after each refresh interval.
When a computer starts up, its current settings are modified first by any configuration specified by the local policy. Then, the configuration in group policies is applied: first, the policies linked to the computer's site, then the policies for its domain, and finally the policies for each OU in the branch that leads to the computer's OU. If there is ever a conflict in a particular configuration setting, the last setting applied takes effect. Therefore, the policies that are "closest" to the computerfor example, the policies linked to its OUtake precedence if a conflict arises. The same application of policies applies to a user at logon: local policy, site policy, domain policy, and OU policy.
You can remember the order of policy application as LSDOU, or "el-stew." Policies are applied in the order local, site, domain, and OU.
The process of applying group policy settings is an intuitive process, at first. But applying group policy can get extremely complex when multiple policy settings are applied to a single container (SDOU), when inheritance is blocked or No Override is specified, and when policies are modified by access control lists (ACLs). Luckily, the enterprise scale application of group policy is not an objective of the Windows 2000 Professional exam. You need to simply understand the basic order of policy applicationlocal, site, domain, and OU (LSDOU).
Group Policy and OU Design
Group policy is a major factor in determining an enterprise's OU structure. If an OU contains users or computers that require different configurations and settings, the best practice is to create separate OUs, each of which contains objects that are configured similarly. By doing so, you can then manage the configuration by applying an appropriate group policy to each OU.
For example, think about the organization depicted in Figure 3.2. If within the Marketing OU a group of salespeople needed a sales application, and that sales application was not appropriate for all users in the Marketing OU, the best practice would be to create an OU, perhaps called Sales, within the Marketing OU (see Figure 3.3). If you place the Sales OU within the Marketing OU, the Sales OU inherits all the existing administration and configuration of the Marketing OU. But you can create a policy linked only to the Sales OU, and you can use that policy to deploy the sales application. As users are moved into the Sales OU, the sales application is deployed to them. See Chapter 4, "Configuring and Troubleshooting the User Experience," for more information about deploying applications through group policy.
Figure 3.3 The Sales OU within the Marketing OU.