What is Active Directory?

Active Directory or A.D. is the antithesis of NT 4.0's LanManager. It is essentially a database of network resources(known as objects) and information about each of these objects. This is not a new concept as Novell and Banyan have used directory services for years. Familiarity with Novell 4.11 will greatly improve the time it takes to become comfortable with this new network management system as many of AD's features and terminology are very similar to that of Novell Directory Services(NDS). Why Active Directory? While NT 4.0 was a pretty good networking operating system, it wasn't entirely equipped for enterprise networking. The network neighborhood was a great tool until you had a huge network, then browsing problems would begin and finding a particular printer or server could become a nightmare especially if you didn't know the name of it. Furthermore, in order to even accomodate such a network, you would most likely have to partition it into several domains connected with trust relationships. AD solves many of these problems and offers a new level of scalability and orginization for enterprise computing. The directory of each domain can store as many as 10 million objects which is enough to accommodate millions of users per domain. Directory Architecture: First let's introduce the concept of "Sites". Sites are used to define the boundaries of high-speed links on a network containing Active Directory Servers. Sites are based on IP subnets and are defined as a "well-connected subnet or subnets". Do not confuse this term with the concept of domains which are discussed next. One thing that hasn't changed from NT 4.0 is the use of domains. A domain is still the centerpiece of a Windows 2000 network, however, it is set up differently. Domain controllers are no longer separated into PDCs and BDCs. Now there are simply DCs(Domain Controllers). By default, all Win2K servers are installed as Standalone Member Servers. DCPROMO.EXE is the Active Directory Installation Wizard and is used to promote a non-domain controller to a DC and vice versa. The wizard prompts for all of the required information to install Active Directory under the conditions that you have asked it to run Knowledge Consistency Checker(KCC) - This is a service created in order to ensure that the Active Directory service in the Windows 2000 operating system can replicate properly, runs on all DCs and automatically establishes connections between individual computers in the same site. These are known as Active Directory connection objects. An administrator can establish additional connection objects or remove connection objects, but at any point where replication within a site becomes impossible or has a single point of failure, the KCC steps in and establishes as many new connection objects as necessary to resume Active Directory replication. Each domain controller in a domain is capable of accepting requests for changes to the domain database and replicating that information with the other DCs in the domain. The first domain that is created is referred to as the "root domain" and is at the top of the directory tree. All subsequent domains will live beneath the root domain and are referred to as child domains. The child domain names must be unique. As you are viewing the items below, pay attention to how Windows 2000 now supports internet naming conventions.
When a root domain and at least 1 child domain have been created, a "tree" is formed. Remember and understand this term as you will hear it often when working with a directory service.