Physical versus Logical Structure
The logical structure of Active Directory design is represented by the domains, their relationships with one another, along with the organizational units (OUs). These relationships are represented in domain and OU topologies, as seen in Figure 10.1
Figure 10.1. A domain tree with parent and child domains.
Sites represent the physical network within Active Directory. DCs communicating within a site behave differently than DCs communicating across sites. Furthermore, because we want clients to communicate with DCs located on the network near them, clients are also site aware.
The network topology and the desired domain topology are the basis for site design, as shown in Figure 10.2. It is important to understand the network, as well as the business, requirements driving your domain topology when constructing your site design. Therefore, understand your current and future network design before designing your site topology.
Figure 10.2. Documented physical network topology.
Properly mapping the physical topology to the logical topology increases the efficiency of client access, increases the efficiency and availability of resources, reduces replication latency, and helps to ensure that Active Directory provides the return on investment promised. See Figure 10.3 for an example domain topology.
Figure 10.3. Domain topology over physical topology.
