I've written quite a few articles on the subject of Windows 2000 security. Most of these articles focus on advanced topics, such as symmetric multikey encryption, or digital certificates. However, some of the lower-end security mechanisms can be just as important. For example, in this article, I'll be discussing group-related security. Although a group is nothing more than a collection of users or other resources, groups are one of the most important security structures in Windows 2000. Implementing groups incorrectly (or not at all) can lead to all sorts of problems, like conflicting permissions or a security scheme that's impossible to manage.
Why Use Groups?
If a group is simply a collection of users, you may wonder what the big deal is about using them. After all, nothing in Windows 2000 stops you from assigning permissions to individual users. However, it's much easier to work with groups than with individual user accounts. For example, suppose you make a new application available to the users. Would you rather individually assign permissions to 1000 users, or assign the permissions to a single group?
Convenience in assigning permissions is not the only reason to use groups. In fact, groups should be the backbone of your security infrastructure. Microsoft recommends that you never assign permissions of any kind to an individual, but rather assigning all permissions on a group basis. Unfortunately, without a good understanding of the different types of groups and their specific functions, it's easy to make a mess out of your security architecture. In this article, I'll discuss the various types of Windows 2000 groups. Once you're familiar with the various types of groups, I'll continue the discussion in Part 2 of this series by discussing how the various types of groups interact with each other.
Distribution Groups vs. Security Groups
If you have a background in Windows NT, then you know that NT contains only one native type of group. However, the Windows 2000 Active Directory supports two types of groups: distribution groups and security groups. Distribution groups aren't related to security issues; they're only used for grouping users (or other resources) for non-security-related purposes. For example, if you often need to send an e-mail message to all the managers in the company, you can group the managers into a distribution group and send the e-mail message to the group rather than to individual people.
Security groups, on the other hand, are more like the groups in Windows NT. You can use a security group to assign a group of people access to an application, directory, or other resource. You can use security groups as distribution groups, but you can't use distribution groups as security groups.
Now let's look at another important issue: group scopes. A group's scope refers to how and where you can use the group to assign security permissions. Windows NT used two basic group scopes: global groups and local groups. Windows 2000 uses global and local groups, and adds two more scopes: universal groups and domain local groups.
Local groups are used to protect resources on workstations or member servers. As you may recall, workstations and member servers all maintain their own security accounts database, which functions independently from the SAM or the Active Directory. These local security accounts allow you to locally access a machine whether it's connected to a network or not.
Local groups are a way to restrict local resources from these accounts. For example, suppose you have a single PC in the office that everyone takes turns using. If only three people need access to a particular directory, you can create a local group on the PC that regulates access to that directory.
You should be aware of a few rules that apply to local groups:
- Local group membership is limited to accounts from the local machine.
- Local groups can't be part of other groups.
- You can't create local groups on domain controllers, because domain controllers don't keep a set of security accounts that function separately from the domain security accounts.