A domain controller
(DC) can be authoritative for one and only one domain. It is not possible to host multiple domains on a single DC. For example, Distributednetworks has already been allocated a DNS domain name for its company called distributednetworks.com, so it decides that the first Active Directory domain that it is going to build is to be named distributednetworks.com.
However, this is only the first domain in a series that may need to be created, and distributednetworks.com is in fact the root of a domain tree
The distributednetworks.com domain itself is automatically created as the root node of a hierarchical structure
called a domain tree. This is literally a series of domains connected together in a hierarchical fashion, all using a contiguous naming scheme.
If Distributednetworks were to add domains called Europe, Asia, and Americas, then the names would be
- asia.distributednetworks.com, and
Each domain tree is called by the name given to the root of the tree; hence, this domain tree is known as the distributednetworks.com tree.
You can see that in the setup of Distributednetworks we now have a contiguous set of domains
that all fit into a tree. Even if we had only one domain, it would still be a domain tree
with one domain.