Domain Name Server (DNS) System

As you learned earlier, the Internet runs on the Client-Server model of computing. Two of the primary questions in this model are exactly how a client knows which server to query and how to actually get to that server (what route to take). To address the question, the creators of the Internet devised what is now known as the Domain Name Server system to organize and coordinate the interactions between clients and servers on the Internet.

An excellent explanation of how the system works may be found at HowStuffWorks.com -- http://computer.howstuffworks.com/dns.htm. However, a brief summary follows.

Each computer connected to the Internet, regardless of whether it is a client machine or a server (host), has a unique identification number associated with it known as an IP address. The IP address is related to the physical geographic location of the computer.

An IP address is comprised of 4 Octets, with each octet separated by a dot(.) and representing a number between 0 and 255.

An example of an IP address == 137.48.70.2

The first octet is 137; the second octet is 48; and so on...

While computers really only work with information encoded into number systems (binary), humans have a hard time remembering IP addresses. In order to make things easier for us, a name system was devised so that humans need only know the name (and not the IP address) of a host machine in order to access it. This is the Domain Name Server System.

In the Domain Name Server (DNS) System, human-readable names are "mapped" to their IP addresses so that you can type into a client application either the name or the IP address and still be able to reach the right system. When a client requests information from a server, it first contacts a DNS server to get the correct IP address and route.

To ensure that IP addresses are mapped correctly, the ICANN organization maintains a registry of names currently in use. These names (and IP addresses) are categorized by Domain types.

You are probably already familiar with the categorization used in the DNS system. The domain naming conventions are based upon the purpose of the host (domain) server as well as the geographic location of the host (domain) server.

• .EDU == Educational organization, primarily higher education institutions
• .COM == Commercial enterprise
• .ORG == Organizational host/related
• .GOV == Federal Government host/related
• .UK == United Kingdom host
• .CA == Canadian host

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With this background on the Domain Name Server System, we can begin to see how a URL is constructed. In the next section, we'll take a more detailed look at URLs and how they are constructed.

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