DNS Hierarchical Authority Structure and the Distributed Name Database
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I began my description of the DNS name space with a dissertation on the central concept of naming in DNS: that of the domain. Each domain can be considered akin to a sphere of influence or control. A domain spreads its wings over all the objects and subdomains that it contains. Due to this concept of influence, when we consider any DNS name space, we see that it is hierarchical because it reflects a hierarchy of organizations that control domains and the nodes within them. This means that there is in fact a hierarchical authority structure that complements the hierarchical name structure in DNS.
The primary reason why the name space hierarchy leads to an authority hierarchy is the requirement that sibling subdomains be unique within a domain. As soon as we have a need for uniqueness, this means we must have some sort of authority or process that ensures that each subdomain or object picks a different name within that domain. This is in fact what name registration is all about.
This concept of a hierarchical authority structure is a bit abstract, but it's easier to understand if we examine a sample DNS name space and discuss the issues involved in assigning names within it. Naturally, we will want to start at the top of the name hierarchy, with the root domain, null. To start off the name space we must create top-level domains (TLDs) within the root. Now, each of these must be unique, so one authority must manage the creation of all TLDs. This in turn means that the authority that controls the root domain controls the entire name space.
In the case of the Internet, then, this central authority is ultimately responsible for every name in DNS. The central DNS authority for the Internet, which controls the creation of TLDs, was initially called the Network Information Center. It was later the Internet Assigned Numbers Authority (IANA), which is also responsible for protocol numbers, IP addresses and more. These functions are now shared by IANA and the Internet Corporation for Assigned Names and Numbers (ICANN). We'll discuss the specific TLDs of the Internet in the next few topics; IANA/ICANN and related organizations are discussed in the topic on Internet registration authorities.
At the next level down in the authority hierarchy, we create second-level domains within each of the TLDs. Each TLD must itself be managed using a coordinating authority, however, this is not necessarily the organization that runs the root (IANA). IANA delegates authority for some of the TLDs to other organizations. They may delegate control for each TLD to a different authority at this level of the hierarchy. In fact, there can be completely different rules for managing the creation of second-level domains in one TLD than there are in another.
We'll see more of how this works later in the section. We'll also discover that in some TLDs there are in fact multiple authorities that work together on name registration.
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