How do I create a new Active Directory site?

A. Active Directory (AD) has sites, which you can use to group servers into containers that mirror your network’s physical topology. Sites also let you configure replication between domain controllers (DCs). In addition, you can map several TCP/IP subnets to sites so that new servers can automatically join the correct site depending on their IP address and so that clients can easily find the DC closest to them.

When you create the first DC, AD creates the default site Default-First-Site-Name and assigns the DC to this site. Subsequent DCs also add to this site, although you can later move the DCs to other sites. You can rename the default site if you want.

You use the Microsoft Management Console (MMC) Active Directory Sites and Services Manager snap-in to create and administer sites. To create a new site, perform the following steps.

IP

After you create the site, you can assign various IP subnets to the site as follows.

After you have a subnet linked to a site, you can assign multiple subnets to the site.

Determining the bits masked portion of the subnet name can be confusing. This value is the number of bits set in the subnet mask, which ranges from 22 to 32. The subnet mask consists of four sets of 8 bits. You can use the following Figure to convert the subnet mask to bits.

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For example, the subnet mask 255.255.255.0 is 11111111.11111111.11111111.00000000 in binary, which uses 8 + 8 + 8 bits (i.e., 24) to define the subnet mask. The subnet mask 255.255.252.0 is 11111111.11111111.11111100.00000000 in binary, which is 8 + 8 + 6, or 22.

After you define multiple sites, new DCs that you use DCPROMO to create will automatically join the site that matches their IP address. If no site exists for a DC’s IP subnet, the DC will join the site that authorized the DC’s promotion.