Every Active Directory Forest includes at least one site.
You should create additional sites when you have the following scenarios a slow link separates part
of the network or a part or a part of the network has enough users to warrant host and domain controllers
or other services in that location.
Or you want to control service location and localization or you want to control replication between
domain controllers.
Let's review each of these scenarios a slow link separates part of the network.
As previously mentioned a site is characterized by a location with fast reliable inexpensive connectivity
if two locations are connected by a slow link you should configure reach location as a separate edit
inside a slow link typically is one that has a connection of less than 512 killer bits per second.
The next scenario is a part of network has enough users to warrant host and domain controllers or other
services in that location.
Concentrations of users also can influence your assigned design.
If a network location has a sufficient number of users for whom the inability to authenticate would
be problematic place a domain controller in the location to support authentication within the location.
After you place a domain controller or other distributed service and allocation that will support those
users you might want to manage a tedious application to the location or localized service by configuring
an active directory site to represent their location.
The next scenario is that you want to control service localization by establish an entity as sites you
can ensure that clients use domain controllers that are nearest to them for authentication which reduces
authentication lent latency and traffic on when connections.
In most scenarios each site will contain a domain controller.
However you might configure sites to a localized services other than authentication such as DFS windows
branch cache and exchange server services.
In this case some sites might be configured without a domain controller and the less Samarra is when
you want to control replication between domain controllers scenarios might exist in which to well-connected
domain controllers are allowed to communicate only at certain times of the day.
Great insights allow you to control how and when replication takes place between domain controllers.