DNS Is a Hierarchic, Distributed Database

DNS's hierarchy is the result of two things. The most obvious is the domain names, such as www.amazon.com. This is a hierarchic name that is read from left to right. Rightmost is com, which is one of the many hundreds of top-level domains, or TLDs. Of these TLDs, com, edu, and org are the most well-known, but many, many others exist one for each nation and territory on the planet. The International Standards Organization (ISO) has a standard for two-letter country codes called ISO-3166. The Internet authorities simply adopted these codes as names for these national domains. Under each TLD several more domains exist, such as amazon in our example. In addition, within the amazon domain, you find several more domain names, including the name of a machine (or several machines sharing one name), such as www. Together, the domain names make up www.amazon.com, which is called a fully qualified domain name (FQDN) because no part of the name is left out. Both TLD and FQDN are acronyms often found in technical discussions on the Internet.

However, the hierarchy also comes from one other thing, which is linked with the distribution. Distribution is the way in which the contents of the DNS database are dispensed among servers on the Net. These make a hierarchy, almost in direct relation to the domain name structure. Authorities on the Net, called registrars, have authority over com and the other TLDs. They give, or delegate, authority over subdomains to the people who manage those subdomains. For instance, people employed by Amazon manage the amazon.com part of the database with their own set of DNS servers that have authority over the amazon.com domain. It is even possible for Amazon, or any other entity, to have several subdomains with delegated authority. This delegation of authority from com to amazon is a very important feature because it distributes both the administrative and technical responsibilities of managing DNS throughout the Net. Herein lies the point of DNS and the reason it can keep growing while the hosts.txt file could not. The delegation of authority over subdomains ensures that DNS is scalable; no single part of DNS will be bogged down by the weight of its responsibilities.