In computer networking, a domain name is a name given to a collection of network devices that belong to a domain which is managed according to some common property of the members or within a common administrative boundary. In particular, the term is used to describe the regions of administrative authority within the Domain name system used for the Internet.
It is a name that identifies one or more IP addresses. For example, the domain name microsoft.com represents about a dozen IP addresses. Domain names are used in URLs to identify particular Web pages. For example, in the URL http://www.pcwebopedia.com/index.html,the domain name is pcwebopedia.com.
Every domain name has a suffix that indicates which Top Level Domain (TLD) it belongs to. There are only a limited number of such domains. For example:
• gov - Government agencies
• edu - Educational institutions
• org - Organizations (nonprofit)
• mil - Military
• com - commercial business
• net - Network organizations
• ca - Canada
• th - Thailand
The Internet is based on IP addresses, not domain names, every Web server requires a Domain Name System (DNS) server to translate domain names into IP addresses.
Uniform Resource Locator (URL)
URL is the global address of documents and other resources on the World Wide Web.
The first part of the address is called a protocol identifier and it indicates what protocol to use and the second part is called a resource name and it specifies the IP address or the domain name where the resource is located. The protocol identifier and the resource name are separated by a colon and two forward slashes.
For example, the two URLs below point to two different files at the domain pcwebopedia.com.The first specifies an executable file that should be fetched using the FTP protocol; the second specifies a Web page that should be fetched using the HTTP protocol:
ftp://www.pcwebopedia.com/stuff.exehttp://www.pcwebopedia.com/index.html
IP Addresses
IP Address is an identifier for a computer or device on a TCP/IP network.
An IP address (Internet Protocol Address) is a logical address of a network adapter.
The IP address is unique and identifies computers on a network.
An IP address can be private, for use on a LAN, or public, for use on the Internet or other
WAN.
IP address can be changed and hidden
Networks using the TCP/IP protocol route messages based on the IP address of the destination. The format of an IP address is a 32-bit numeric address written as four numbers separated by periods. Each number can be zero to 255. For example, 1.160.10.240 could be an IP address.
Within an isolated network, you can assign IP addresses at random as long as each one is unique. However, connecting a private network to the Internet requires using registered IP addresses (called Internet addresses) to avoid duplicates.
The four numbers in an IP address are used in different ways to identify a particular network and a host on that network. Four regional Internet registries -- ARIN, RIPE NCC, LACNIC and APNIC -- assign Internet addresses from the following three classes.
Class A - supports 16 million hosts on each of 126 networks Class B - supports 65,000 hosts on each of 16,000 networks
Class C - supports 254 hosts on each of 2 million networks
The number of unassigned Internet addresses is running out, so a new classless scheme called CIDR is gradually replacing the system based on classes A, B, and C and is tied to adoption of IPv6.
Web Server
A web server is a computer that delivers (serves up) Web pages. Every Web server has an IP address and possibly a domain name. For example, if you enter the URL http://www.pcwebopedia.com/index.htmlin your browser, this sends a request to the server whose domain name is pcwebopedia.com. The server then fetches the page named index.html and sends it to your browser.
Any computer can be turned into a Web server by installing server software and connecting the machine to the Internet. There are many Web server software applications, including public domain software from NCSA and Apache, and commercial packages from Microsoft, Netscape and others.
How Web Servers Work
Have you ever wondered just exactly how a Web page you are reading found its way into your browser and onto your computer screen? The process largely depends on Web servers
Typically, users visit a Web site by either clicking on a hyperlink that brings them to that site or keying the site's URL directly into the address bar of a browser. But how does the same site appear on anyone's computer anywhere in the world and often on many computers at the same time?
Let's use Webopedia as an example. You decide to visit Webopedia by typing its URL -- http://www.webopedia.com -- into your Web browser. Through an Internet connection, your browser initiates a connection to the Web server that is storing the Webopedia files by first converting the domain name into an IP address (through a domain name service) and then locating the server that is storing the information for that IP address (also see Understanding IP Addressing).
The Web server stores all of the files necessary to display Webopedia's pages on your computer -- typically all the individual pages that comprise the entirety of a Web site, any images/graphic files and any scripts that make dynamic elements of the site function.
Once contact has been made, the browser requests the data from the Web server, and using HTTP, the server delivers the data back to your browser. The browser in turn converts, or formats, the computer languages that the files are made up of into what you see displayed in your browser. In the same way the server can send the files to many client computers at the same time, allowing multiple clients to view the same page simultaneously.
Domain Name System (DNS)
The Domain Name System (DNS) is the way that Internet domain names are located and translated into Internet Protocol addresses. A domain name is a meaningful and easy-toremember "handle" for an Internet address.
Maintaining a central list of domain name/IP address correspondences would be impractical, the lists of domain names and IP addresses are distributed throughout the Internet in a hierarchy of authority. There is probably a DNS server within close geographic proximity to your access provider that maps the domain names in your Internet requests or forwards them to other servers in the Internet.
The Domain Name System (DNS) associates various information with domain names; most importantly, it serves as the "phone book" for the Internet by translating human-readable computer hostnames, e.g. www.example.com, into IP addresses, e.g. 208.77.188.166, which networking equipment needs to deliver information. A DNS also stores other information such as the list of mail servers that accept email for a given domain. By providing a worldwide keyword-based redirection service, the Domain Name System is an essential component of contemporary Internet use.
The domain Name Space
The domain name space consists of a tree of domain names. Each node or leaf in the tree has zero or more resource records, which hold information associated with the domain name. The tree sub-divides into zonesbeginning at the root zone. A DNS zone consists of a collection of connected nodes authoritatively served by an authoritative DNS name server. (Note that a single name server can host several zones.)
When a system administrator wants to let another administrator control a part of the domain name space within the first administrator’s zone of authority, control can be delegated to the second administrator. This splits off a part of the old zone into a new zone, which comes under the authority of the second administrator's name servers. The old zone ceases to be authoritative for the new zone.
Parts of a Domain Name
• A domain name usually consists of two or more parts (technically a label), which is conventionally written separated by dots, such as example.com.
• The rightmost label conveys the top-level domain (for example, the address www.example.com has the top-level domain com).
• Each label to the left specifies a subdivision, or sub domain of the domain above it. Note: “sub domain” expresses relative dependence, not absolute dependence. For example: example.comis a sub domain of the comdomain, and www.example.comis a sub domain of the domain example.com. In theory, this subdivision can go down 127 levels. Each label can contain up to 63 octets. The whole domain name may not exceed a total length of 253 octets.
In practice, some domain registries may have shorter limits.
• A hostname refers to a domain name that has one or more associated IP addresses; i.e. the
'www.example.com' and 'example.com' domains are both hostnames, however, the 'com' domain is not.
DNS Servers
The Domain Name System is maintained by a distributed database system, which uses the client-server model. The nodes of this database are the name servers. Each domain or sub domain has one or more authoritative DNS servers that publish information about that domain and the name servers of any domains subordinate to it. The top of the hierarchy is served by the root name servers
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