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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 most important element of a name system's name space is its name architecture, which describes how names are constructed and interpreted. The architecture of the Domain Name System is, unsurprisingly, based on the concept of an abstraction called a domain. This is obviously a good place to start in explaining how DNS works. Unfortunately, it's not the easiest concept to explain from scratch, so as usual, I'll do my best and ask for your patience. J

Dictionary definitions of the word “domain” generally convey the notion of a sphere of influence, or area of control or rulership. An essential concept is that in many different contexts, control or authority can be exerted at many different levels. One sphere of influence may contain smaller ones, which can in turn contain smaller ones still. This means that such domains are naturally arranged in a hierarchy.

An obvious example would be geopolitical domains. We have no centralized “world government” on earth, but we do have the United Nations, which deals with world-wide issues. At the next level down, we have individual countries. Some of these countries have divisions such as states and provinces. Still lower levels have counties, municipalities, neighborhoods and individual residences or businesses. The “domains” are inherently hierarchical in organization.

The Domain Name System uses the word domain in a manner very similar to this, and employs a hierarchical structure that works in much the same way as the geopolitical example. In DNS, a domain is defined as either a single object or a set of objects that have been collected together based on some type of commonality. Usually in DNS that commonality is that they are all administered by the same organization or authority, which makes the name hierarchy tightly linked to the notion of the DNS hierarchical authority 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