What are group policies?
Group policies specify how programs, network resources, and the operating system work for users and computers in an organization. They are collections of user and computer configuration settings that are applied on users and computers (not on groups). For better administration of group policies in the Windows environment, the group policy objects (GPOs) are used.
What is GPO?
Group policy object (GPO) is a collection of group policy settings. It can be created using a Windows utility known as the Group Policy snap-in. GPO affects the user and computer accounts located in sites, domains, and organizational units (OUs). Windows operating systems support two types of GPOs, local and non-local (Active Directory-based) GPOs.
Local GPOs
Local GPOs are used to control policies on a local server running Windows Server 2003/2008. On each Windows server, a local GPO is stored. The local GPO affects only the computer on which it is stored. By default, only Security Settings nodes are configured. The rest of the settings are either disabled or not enabled. The local GPO is stored in the %systemroot%SYSTEM32GROUPPOLICY folder.
Non-local GPOs
Non-local GPOs are used to control policies on an Active Directory-based network. A Windows server needs to be configured as a domain controller on the network to use a non-local GPO. Non-local GPOs must be linked to a site, domain, or organizational unit (OU) to apply group policies to the user or computer objects. Non-local GPOs are stored in %systemroot%SYSVOL<domain name>POLICIES<GPO GUID>ADM, where <GPO GUID> is the GPO’s globally unique identifier. Two non-local GPOs are created by default when the Active Directory is installed:
- Default Domain Policy: This GPO is linked to the domain and affects all users and computers in the domain.
- Default Domain Controllers Policy: This GPO is linked to the Domain Controllers OU and affects all domain controllers placed in this OU.
Multiple GPOs
When multiple group policy objects are assigned, the group policies are applied in the following order:
- The local group policy object is applied first.
- Then, the group policy objects linked to sites are applied.
If multiple GPOs exist for a site, they are applied in the order specified by an administrator.
- GPOs linked to the domains are applied in the specified order.
- Finally, GPOs linked to OUs are applied.
The OU group policy objects are set from the largest to the smallest organizational unit, i.e., first the parent OU and then the child OU.
By default, a policy applied later overwrites a policy that was applied earlier. Hence, the settings in a child OU can override the settings in the parent OU.
Group policy settings are cumulative if they are compatible with each other. In case they conflict with each other, the GPO processed later takes precedence.
The following are the exceptions with regard to the above-mentioned settings:
- No Override: Any GPO can be set to No Override. If the No Override configuration is set to a GPO, no policy configured in the GPO can be overridden. If more than one GPO has been set to No Override, then the one that is the highest in the Active Directory hierarchy takes precedence.
- Block Policy Inheritance: The Block Policy Inheritance option can be applied to the site, domain, or OU. It deflects all group policy settings that reach the site, domain, or OU from the object higher in the hierarchy. However, the GPOs configured with the No Override option are always applied.
- Loopback setting: By default, users settings override computer settings in case of any conflict in policy settings. By configuring the loopback setting, an administrator can reverse the process of the application of policies. When the Loopback option is configured, the computer settings take precedence on the users settings. The Looback option can be set as Not Configured, Enabled, or Disabled. The enabled Loopback option can be set in the following two modes:
- Replace mode: In this mode, the computer policy settings override the user policy settings.
- Merge mode: In this mode, the computer policy settings are appended to the user policy settings.
Note: The computers that are members of a workgroup are not affected by the non-local GPOs policy settings. They process only the local GPOs.
Group Policy Inheritance
The group policies are inherited from a parent to a child within a domain. They are not inherited from the parent domain to a child domain. The ollowing are the rules regarding group policy inheritance:
- A policy setting is configured (Enabled or Disabled) for a parent OU, and the same policy setting is not configured for its child OUs. The child OUs inherit the parent’s policy.
- A policy setting is configured (Enabled or Disabled) for a parent OU, and the same policy setting is configured for its child OUs. The child OUs settings override the settings inherited from the parent’s OU.
- If any policy is not configured, no inheritance takes place.
- Compatible policy settings configured at the parent and child OUs are accumulated.
- Incompatible policy settings from the parent OU are not inherited.
Filtering Scope of GPOs
Although GPOs are linked to the site, domain, or OUs, and they cannot be linked to the security groups directly, applying permissions to the GPO can filter its scope. The policies in a non-local GPO apply only to users who have the Read and Apply Group Policy permissions set to Allow. By specifying appropriate permissions to the security groups, the administrators can filter a GPO’s scope for the computers and users.
Note: The Apply Group Policy permission is not available with the local GPO.
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