Active Directory 2008 : Implementing Sites and Subnets (part 1) - Creating Sites

Now that you have an idea of the goals of replication, look at the following quick overview of the various Active Directory objects that are related to physical network topology.

The basic objects that are used for managing replication include the following:

Subnets

A subnet is a partition of a network. As we started to discuss earlier, subnets are logical IP blocks usually connected to other IP blocks through the use of routers and other network devices. All of the computers that are located on a given subnet are generally well connected with each other.

Sites

An Active Directory site is a logical object that can contain servers and other objects related to Active Directory replication. Specifically, a site is a grouping of related subnets. Sites are created to match the physical network structure of an organization. Sites are primarily used for slow WAN links. If your network is well connected (using fiber optics, Category 5 Ethernet, etc.), then sites are not needed.

Site links

A site link is created to define the types of connections that are available between the components of a site. Site links can reflect a relative cost for a network connection and can reflect the bandwidth that is available for communications.

All of these components work together to determine how information is used to replicate data between domain controllers. Figure 1 provides an example of the physical components of Active Directory.

Figure 1. Active Directory replication objects

Many issues are related to configuring and managing sites. Overall, using sites allows you to control the behavior of Active Directory replication between domain controllers. With this background and goal in mind, let's look at how you can implement sites to control Active Directory replication so that it is efficient and in synch.

If you do not have replication set up properly, you will experience problems with your domain controllers after awhile. An example of a common replication problem is Event Log event ID 1311, which states that the Windows NT Directory Services (NTDS) Knowledge Consistency Checker (KCC) has found (and reported) a problem with Active Directory replication. This error message states that the replication configuration information in Active Directory does not accurately reflect the physical topology of the network. This error is commonly found on ailing networks that have replication problems for one reason or another.

1. Creating Sites

The primary method for creating and managing Active Directory replication components is to utilize the Active Directory Sites And Services tool or the MMC found within the Administrative Tools folder. Using this administrative component, you can graphically create and manage sites in much the same way you create and manage OUs.

Exercise 1 walks you through the process of creating Active Directory sites. In order for you to complete this exercise, the local machine must be a domain controller. Also, this exercise assumes that you have not yet changed the default domain site configuration.