Introduction to Domain

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Domain: A domain is an area of control or sphere in knowledge 

 Uniform Resource Identifiers and Domain Names

URIs and URLs

A Uniform Resource Identifier (URI) identifies a resource on the Internet. A Uniform Resource Locator (URL) is a type of URI which represents the network location of a resource such as a web page, a graphic file, or an MP3 fileThe URL consists of the proto- col, the domain name, and the hierarchical location of the file on the web server. The URL http://www.webdevfoundations.net, shown in Figure 1.8, denotes the use of HTTP protocol and the web server named www at the domain name of webdevfoundations.netIn this case, the root file (usually index.html or index.htm) in the directory named chapter1 will be displayed



Domain Names

A domain name locates an organization or other entity on the Internet. The purpose of the domain Name System (DNS) is to divide the Internet into logical groups and understand- able names by identifying the exact address and type of the organization. The DNS asso- ciates the text-based domain names with the unique numeric IP address assigned to a device.

Let's consider the domain name www.google.com. The portion "google.com" is the domain name that is registered to Google. The "com" is the top-level domain name. The "google" is considered a second-level domain name. The "www" is the name of the web sever (sometimes called the host) at the google.com domain.

A subdomain can be configured to house a separate website located at the same domain. For example, Google's Gmail can be accessed by using the subdomain "gmail" in the domain name (gmail.google.com). Google Maps can be accessed at maps.google.com, and Google News Search is available at news.google.com. See http://www.labnol.org/ internet/popular-google-subdomains/5888/ for a list of the top 40 Google subdomains. The combination of a host/subdomain, second-level domain, and top-level domain name (such as www.google.com or mail.google.com) is called a fully qualified domain name (FQDN)

Top-Level Domain Names

A top-level domain (TLD) identifies the rightmost part of the domain name, starting with the final period. A TLD is either a generic top-level domain (gTLD), such as .com for commercial or a country-code top-level domain, such as fr for France. The Internet Assigned Numbers Authority (IANA) website has a complete list of TLDs (http://www.iana.org/domains/root/db).

Generic Top-Level Domain Names (gTLDs)

The Internet Corporation for Assigned Names and Numbers (ICANN) administers gTLDs (http://www.icann.org). Table 1.1 shows several common gTLDs and their intended use

The .com, .org, and .net TLD designations are currently used on the honor system, which means that, for example an individual who owns a shoe store (not related to networking) can register shoes.net. Expect the number and variety of gTLDs to increase. As of 2017 there were over 1,500 TLDs. The new gTLDs include place names (quebec, vegas, and moscow), retail terms (.blackfriday), financial terms (.cash, trade, and loans), technology terms (.systems, technology, and app), and whimsical, fun terms (.ninja, buzz, and cool).

ICANN has set a schedule to periodically launch new gTLDs. Visit http://newgtids.icann .org/en/program-status/delegated-strings for a list of the newest gTLDs.

Country-Code Top-Level Domain Names

Two-character country codes have also been assigned as TLD names. These codes were originally intended to be meaningful by designating the geographical location of the indi- vidual or organization that registered the name. Table 1.2 lists some popular country codes used on the Web.

The IANA website at http://www.iana.org/domains/root/db has a complete list of country-code TLDs. Domain names with country codes are often used for municipalities, schools, and community colleges in the United States. For example, the domain name www.harper.cc.il.us denotes, from right to left, the United States, Illinois, community col- lege, Harper, and the web server named "www" as the site for Harper College in Illinois.

Although country-code TLD names were intended to designate geographical location, it is fairly easy to obtain a domain name with a country-code TLD that is not local to the registrant. Examples of non-geographical use of country-code TLDs include domain names such as mediaqueri.es, webteacher.ws, and bit.ly. Visit http://register.com, http://godaddy.com, and many other domain name registration companies for examples of readily available country-code TLDs.

Domain Name System (DNS)

The DNS associates domain names with IP addresses. The following happens each time a new URL is typed into a web browser:

1. The DNS is accessed.

2. The corresponding IP address is obtained and returned to the web browser

3. The web browser sends an HTTP request to the destination computer with the corresponding IP address.

4. The HTTP request is received by the web server. 5. The necessary files are located and sent by HTTP responses to the web browser,

5. The necessary files are located and sent by HTTP responses to the web browser,

6. The web browser renders and displays the web page and associated files. We all get impatient sometimes when we need to view a web page. The next time you wonder why it is taking so long to display a web page, think about all of the processing that goes on behind the scenes before the browser receives the files needed to display the web page (Figure 1.9).

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