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 Registration, Public Administration, Zones and Authorities

DNS Hierarchical Authority Structure and the Distributed Name Database 1 2 3 4 DNS Geopolitical (Country Code) Top Level Domains and Authorities

Original Generic TLDs

The initial deployment of DNS featured a set of seven top-level domains that are in the standard called generic TLDs. The idea was that each company or organization could choose a name within one of these TLDs; they were “generic” enough that every organization would find a place that suited them. I prefer to call them organizational, because they divide the generic portion of the name space by organization type. The initial TLDs and their original intended organization types were:

• .ARPA: A temporary domain used many years ago for transition to DNS. Its name refers to the ARPAnet, the precursor of the modern Internet (in turn named for the United States Defense Advanced Research Projects Agency, ARPA). Today this domain is used for reverse name resolution.
  
  
• .COM: Corporations and businesses.
  
  
• .EDU: Universities and other educational organizations.
  
  
• .GOV: Government agencies.
  
  
• .MIL: Military organizations.
  
  
• .NET: Organizations that implement, deal with or manage networking technologies and/or the Internet.
  
  
• .ORG: Other organizations that don't fit into any of the classifications above.

At first glance this seems like a reasonable way to cover the organizations of the world. However, since the .ARPA domain is “temporary”, this left only six categories for all other organizations. Also, the TLDs weren't all used as was originally foreseen; for example, the .GOV and .MIL domains were not used for all types of government and military organizations, but primarily for the United States federal government and military. .EDU ended up being used only for universities, again in the United States.

This left only three common top-level domains—.COM, .NET and .ORG—for almost all other groups and companies that wanted to use the organizational hierarchy. Since there were only three such TLDs, they quickly became very “crowded”, especially the .COM domain. A new fourth domain, .INT for international organizations, was added fairly soon to the original seven, but it too was only for a small number of organizations, such as international standards bodies. Despite the handful of organizational TLDs, there is no doubt that they have been much more popular than the geopolitical ones. I explain some of the reasons for this in the next topic.

DNS Hierarchical Authority Structure and the Distributed Name Database 1 2 3 4 DNS Geopolitical (Country Code) Top Level Domains and Authorities