You need to create all the subnets in your organization and assign them to the appropriate sites. You can resynchronize subnets when necessary and delete any subnets that no longer exist.

Subnets can be determined from basic inventory data, imported from Active Directory, or added manually. You can run a subnet import rule to automatically collect the subnet information from Active Directory.

Subnets are always suffixed with the number of bits that are set in the network mask, for example, 192.168.0.0/24. The subnets are always displayed in a hierarchical tree. Resource scoping applies, so you can see only the subnets that contain resources to which you have access.

You need to assign each subnet to the appropriate site. By default, any encompassed subnets (a subnet whose IP range is wholly contained within another subnet) are automatically assigned to the same site. However, you can manually override subnet encompassment by explicitly assigning an encompassed subnet to a different site. By default, encompassed subnets are displayed under their parent subnets in the left pane. However, when an encompassed subnet is manually assigned to a different site from its parent, it is displayed under the site to which it is assigned.

Any site servers on a subnet are automatically assigned to the same site as the subnet. This assignment is not broken if you manually assign a site server to a different site. A site server can be manually assigned to any number of sites, in addition to the site that it serves through its subnet assignment.