Wednesday, June 29, 2011

Active Directory Physical Components; Domain Controllers and Sites Explained

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Active Directory is the core component and the central data base of the network based on Microsoft Windows Domain System. Active Directory is the central supervisor of the network objects and security for the Windows Domain System. In a Microsoft Windows Domain environment based on Active Directory, we can find several classifications of its components. Here we discuss the physical components of Active Directory in a domain.
Active Directory comprises of two physical components. They are Domain Controllers and Sites.

Domain Controllers:
Domain Controllers or DCs are Physical Server Machines running Windows Server 2008 (or older versions Windows Server 2003 or Windows 2000 Server), and it contains the Active Directory Database. There can be several Domain controllers in a Microsoft Active Directory based Domain depending on the span of the organization. The primary or first domain controller of the Domain is just called DCs and every added domain controllers are called ADCs or Additional Domain Controllers.

Domain Controllers or the physical servers with the Active Directory data base of a Domain, contains exactly same copy of the Active Directory data base, and it replicates each other in a precise interval. 

Why we require multiple Domain Controllers?
Active directory performs multiple functions in a Domain, from user authentication to Print Server sharing, just to mention. When the organization expands with several users, computers, printers and other resources, we will require setting up multiple Domain Controllers in a domain to equally distribute the work load, which will result easy and speedy   functionality of the network.

Sites are the second major physical component of Active Directory, which organises the network into different physical or geographical locations.  If your network span is only within a single building, Active Directory can work with a Single Site. But if your organization spans into multiple buildings or geographical locations, it’s required to split the Active Directory into multiple sites. It mainly helps reducing high network utilization during replication across WAN links.

How Sites help for Optimized replication?
As we discussed earlier, the Domain Controllers replicates the Active Directory Database each other.  By organizing the Domain Controllers of a particular physical location into its respective sites, we can control the replication traffic. Administrator can set up unlimited replication between Domain Controllers with the same Site, because it’s within the LAN, and he can schedule the replication between two Domain Controllers from different sites for specified interval (like twice a day etc.), because it travels across WAN links. This will help to reduce overloading of WAN links between the two geographical locations of the organization.

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