How to create and configure subnets for Active Directory Sites

A subnet is a portion of the IP space of a network. Subnets are described by their IP network address combined with a subnet mask measured in bits. Click the following links and the to learn more about IP V4 addresses, and Class C Subnetting Tutorials.

The subnet objects in Active Directory are the logical representation of the subnets in your physical network environment.

Subnet information is used to find Domain Controller in the same site and Active Directory replication to determine the best routes between domain controllers.

Subnets must be defined in Active Directory to ensure accurate and efficient directory replication and resource usage.

To create a new subnet, right click the subnets folder and select "New Subnet" from the popup menu.

In the New Object - Subnet dialog box shown below, type the subnet address and the subnet mask that may be used in this site's subnet. Choose a site to associate this subnet (In this example, I have selected "Chennai" site), and then click OK. Note that the CIDR notation of the address is also displayed in the dialog box.

To create another subnet object, again right click the subnets folder and select "New Subnet" from the popup menu.

 

In the New Object - Subnet dialog box shown below, type the new subnet address and the subnet mask that may be used in next site's subnet. Choose another site to associate this subnet (In this example, I have selected "Bangalore" site), and then click OK.

Now you can see the two subnets we have created in this excercise and their associated sites displayed in the "Active Directory Sites and Services snap-in"