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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  Name Systems and TCP/IP Name Registration and Name Resolution            9  TCP/IP Name Systems: Host Tables and Domain Name System (DNS)                 9  TCP/IP Domain Name System (DNS)                      9  DNS Name Space, Architecture and Terminology

DNS Name Space, Architecture and Terminology 1 2 3 DNS Structural Elements and Terminology: Domains, Subdomains, and Nodes; Roots, Leaves and Branches; Parents, Children and Siblings

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.

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 structure.

DNS Name Space, Architecture and Terminology 1 2 3 DNS Structural Elements and Terminology: Domains, Subdomains, and Nodes; Roots, Leaves and Branches; Parents, Children and Siblings