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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 Organizational (Generic) Top Level Domains and Authorities 1 2 3 4 DNS Second-Level and Lower Domains, Delegation of Registration Authority and Public Registration

Country Code TLD Authorities

Each country has the authority to set up its TLD with whatever internal substructure it chooses; again, this is the power of a hierarchical structure. Some countries enforce a further geographical substructure at the lower levels. For example, the .US domain for the United States was originally set up so that all second-level domains were two-letter state abbreviations (this was later changed). Other countries may actually use organizational subdomains within their country code; Great Britain for example has .CO.UK for companies in their country (like .COM but for the UK only; they left off the “M”), and .COM.AU is for corporations in Australia. Other countries may not have any particular substructure at all, especially if they are small.

Interestingly, some very small countries with recognizable codes, especially to English speakers, have used their codes for very creative purposes, including selling or renting the name space to enterprising companies. A good example is the .TV domain, which technically belongs to the island nation of Tuvalu. Of course, to most people, “TV” means something quite different. Some folks thought that domain names ending in “TV” might be popular in the English-speaking world, so they formed a company called “The .TV Corporation” and negotiated with the government of Tuvalu to use the .TV domain. Today, the authority for this TLD is in fact this corporation, headquartered in California! Similar arrangements can be found with the .CC, .NU, .TO and other TLDs.

This serves as a good reminder that the name space is logical and not physical. Obviously, the many computers with “.TV” names are not actually located on a remote island in the South Pacific. Similarly, if a Web site ends with “.CA”, for example, it probably represents a Canadian organization, but that doesn't necessarily mean the Web site itself is actually hosted in Canada.

DNS Organizational (Generic) Top Level Domains and Authorities 1 2 3 4 DNS Second-Level and Lower Domains, Delegation of Registration Authority and Public Registration