Let us consider as a typical example the internet address

which is actually the name of the IP address 128.219.21.147. How did the people who run the Internet come up with that name, and how did we know that www.ustc.org is really a nickname for 128.219.21.147?

The symbolic name of a site is determined by a naming standard known as the Domain Name System or DNS. Each field in a symbolic address corresponds to a single domain. The first field is a host name, which identifies a single computer. The last field is a top level domain. In between are things like department names, organization names, and so on in order of increasing generality.

For example, csep10.phys.utk.edu is a Silicon Graphics computer called csep10 in the Physics Department (phys) of the University of Tennessee at Knoxville (utk), which is an educational institution (edu). On the other hand, the address www.ustc.org is the address for the main server of the U. S. Tech Corps, which explains the ".ustc" in the name, and this is an organization, which explains the ".org" part of the name. Generally, we will term a sequence like 128.169.200.227 an IP address, while we will call the corresponding name csep10.phys.utk.edu the DNS name for the computer with IP address 128.169.200.227.

The six top level domains in the US and some sample addresses are listed in the figure, which is taken from the Networking Chapter of the Computational Science Education Project Electronic Book. Addresses of sites outside the US end with a two-letter country code; some common country codes are also listed in this figure.

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