Now let's talk about sites. The formal definition of a site is one or more well-
connected IP subnets. (Well-connected subnets, usually located in the same facility,
building, etc., are defined as connecting at speeds of 10 Mbs or higher.)
When your network is composed of sites, Active Directory can understand the design of
its underlying infrastructure -- where it's segmented and where slow links are. With
this information, AD can decide how to replicate data.
You may be asking yourself, what is the difference between a site and a domain?
Basically, sites constitute your physical network, while domains represent your network
Say your company has multiple locations worldwide. Even though all the offices
manage their own networks locally, they're still part of the same parent company. You
could logically split up the companywide network into multiple domains, each
representing one location.
When your network is composed of sites, AD can both automatically configure its
replication topology (which you can do manually yourself as well) and aid clients in
locating domain controllers (DCs) for logon authentication. (Users' requests are always
directed to the domain controllers within their site.)
One of the major uses of sites is to facilitate AD's control of replication.
Replication is the process of copying data from one source to multiple destinations to
keep the data synchronized. For example, when you change a person's name on one domain
controller, other DCs will see the name's old value until replication has taken place.
Once replication occurs, all DCs will have the new name in place. Replication is a very
technical topic that I will cover in depth in later articles.
In my next article, we will install Active Directory using the DCPROMO