DNS Hierarchical Authority Structure and the Distributed Name Database
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Lower-Level Authority Delegation
The process of authority delegation continues as we continue down the name space hierarchy. At each level the name space becomes more specific; if we use an organizational hierarchy, like the .COM top-level domain, we generally delegate authority for each second-level domain to the organization whose name it represents. So IBM.COM is managed by IBM, and so forth. Since IBM is huge, it may itself subdivide the authority structure further, but smaller organizations probably won't.
I want to point out explicitly that the authority hierarchy is complementary to the name hierarchy; they are not exactly the same. It is not necessary that there be a different authority for every level of the hierarchy. In many cases a single authority may manage a section of the name space that spans more than one level of the structure. For example, IANA manages the Internet root domain (null) and also the .INT top-level domain, but other TLDs are managed by other organizations. The name hierarchy is divided into zones of authority that reflect the hierarchy of authorities that manage parts of the name space.
It's also worth remembering that authority over a domain doesn't necessarily imply physical control. A domain can contain subdomains that are managed by organizations on different continents, and a single subdomain can contain named devices that are on different continents as well.
Of course, with authority comes responsibility, and the main responsibility an authority has for a domain is registering names within the domain. When a name is registered, a set of data is created for it, which can then be used by internetwork devices to resolve the name into an address, or perform other functions. The set of all the data describing all DNS domains constitutes the DNS name database. Just as registration authority is distributed and hierarchical, this database too is distributed and hierarchical.
In other words, there is no single place where all DNS name information is stored. Instead, DNS servers carry resource records that describe the domains for which they have authority. As we'll see, the fact that this database is distributed has major implications on how name resolution is carried out.
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