Appendix C: Name Resolution Services

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C.3.1 DNS’ Hierarchy

A tree-oriented structure was developed that allows for varying levels of name resolution. All end-nodes are treated like "leaves" on a tree. The domain an end-node is in is like a "branch" of the tree. The container the domains are in is like a bigger branch. The "root" is the bottom of the tree, and is represented by a single "." at the end.

For example, the hostname "WWW.UNOVERICA.COM" consists of three levels. The host portion of the hostname is "WWW" while the domain name is "UNOVERICA" and is subordinate to the "COM" domain.

The "COM" domain is one of the few aggregate container domains on the Internet, and has been set aside by the Internet authorities as the container domain for all commercial organizations. Another example of a container domain is "EDU" which serves as an aggregate domain for educational institutions. Other examples are "GOV", "ORG" and "NET".

There are geographical containers for country-specific resources. For example, the "US" domain is an aggregate container for the United States, and the "UK" domain is responsible for domains specific to the United Kingdom. The two-letter codes are based on the two-letter country codes used by the ISO in Geneva Switzerland.

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