The initial set of top-level domains
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Written by Robert on April 13, 2008 – 5:12 am
An initial set of top-level domains was defined, which included:
com
Commercial organizations.
edu
US colleges that had sufficiently distinguished educational programs (i.e. not every US college).
gov
US federal government organizations.
mil
US military.
net
Networking organizations.
org
Non-commercial organizations and special interest groups.
int
International organizations.
arpa
A special ‘domain’ that has a role in the reverse mapping process – when you have an IP address and want to know the appropriate machine name.
SRI-NIC, and later ICANN, controlled the root servers and the name servers for these top-level domains. A commercial organization seeking to be on the Internet would apply for a domain name within the .com domain. If the application was successful, data on its name server (IP address mainly) would be registered with the .com name server(s). This allowed for domains like ibm.com, hp.com and ford.com. Similarly, the .edu domain included stanford.edu, berkeley.edu and rutgers.edu.
The hierarchical grouping extended to an essentially arbitrary depth (the limit is about 100 levels, though even now it is rare to find a sub-domain that is more than about five levels down). Large organizations could define sub-domains; each sub-domain would have an administrator who would run a name server that handled name–IP lookup requests for machines in that sub-domain. For example, NASA (nasa.gov) has research and construction facilities in Texas, Florida, California and other states in the USA; each of these facilities has its own computer networks. Responsibilities for these networks would be delegated. The name server registered under nasa.gov would not hold data on the names and IP addresses for all of NASA’s machines; instead, it would hold the names and IP addresses for the main name servers in sub-domains, such as jpl.nasa.gov, aerospace.nasa.gov, lerc.nasa.gov and ksc.nasa.gov, along with the names and IP addresses of the few machines at NASA headquarters that were in the nasa.gov domain itself rather than a more specific sub-domain. Ultimately, the administrator at nasa.gov is responsible for everything in NASA’s domain; but most of the work is delegated. The nasa.gov administrator is immediately responsible only for the data in the tables used by the nasa.gov name servers. These data will include the names and IP addresses of those headquarters machines in nasa.gov and the names and IP addresses of the name servers that are responsible for the delegated sub-domains, such as jpl.nasa.gov. This subset of data is the nasa.gov ‘zone’ data.
This hierarchical scheme worked, and remains the basis of the current Internet domain naming system. But it did have to be expanded, for it proved too US-centric, and even for this USA it was unsatisfactory. One expansion was to include more than two hundred additional top-level domains – one for each country, along with a few extras for obscure dependencies (e.g. .bv – Bouvet Island, an uninhabited, ice-covered volcanic island nominally administered by Norway). The .us domain was introduced to allow US state and local governments and other organizations to have web presences (not allowed under the original scheme because the .gov domain is for the US Federal government, while the .edu domain is only for a subset of the tertiary level US educational system).
Individual countries handle their national domain names in different ways. Some, like the UK and Australia, have sub-domains similar to the original top-level domains. Consequently, there are domains like .edu.au, .com.au and .gov.au for educational, commercial and government organizations in Australia. Other countries, such as France, have basically a single-level national domain.
There is considerable pressure by organizations to have a second level domain. A domain name like mycompany.com is generally perceived as having a higher status than mycompany.mp.ca.us or mycompany.com.au. This pressure has led to the introduction of additional top-level domains including .biz, and proposed domains such as .mart and .shop.
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