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DNS Domains and the DNS Hierarchical Name Architecture
(Page 2 of 3)
The DNS Hierarchical Tree Structure of Names
One could construct a tree diagram
with the United Nations on top with lines pointing to each of the countries
on earth. Then, within the United States, for example, we could draw
lines to each of the states; within each state, lines to each county
and so on. The result would be something that looks like an upside-down
tree, as we can see in Figure 235.
This is called a tree structure.
Figure 235: Example of a Global Hierarchical Domain Architecture
This diagram shows an example of hierarchical architecture, based on political divisions. The United Nations is an umbrella organization representing (to one extent or another) all of the worlds nations. It is the root of the tree; underneath it we find individual nations. Each nation then is further subdivided in a manner it chooses; for example, Canada has provinces and territories, and the USA individual states. These can in turn be further subdivided in any number of ways.
Trees are used all over
computing and networking; for example, trees are a type of LAN topology.
For our purposes in explaining DNS, the best example of a tree structure
is the directory tree used to store files on a computer's hard disk
or other storage devices. The root directory is at the top of the structure
and may contain named files and/or named directories. Each directory
can itself contain individual files or subdirectories, which can in
turn contain their own subdirectories, and so on.
The domain name structure in DNS
is conceptually arranged in exactly the same way, only instead of dealing
with files, DNS deals with named objects, usually devices like IP hosts.
The highest level is still the root of the tree. It contains
a number of domains, each of which can contain individual objects (names)
and/or lower-level domains. Lower-level domains can in turn have still
lower-level domains, allowing the tree as a whole to take on an arbitrary
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Version 3.0 - Version Date: September 20, 2005
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