Dns Essay Research Paper Domain Name SystemIntroduction

Dns Essay, Research Paper

Domain Name System

Introduction

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 inURL’s to

identify particular Web pages. For example, in the URL http://www.hotmail.com/ the

domain name is hotmail.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

Because the Internet is based on IP addresses, not domain names, every Web Server

requires a Domain Name System server to translate domain names into IP addresses.

The Internet Protocol addresss is a 32- bit integer. If somebody wants to send a

message it is necessary to include the destination address, but people prefer to assign

machines pronounceable, easily remembered names (host names). For this reason the

Domain Name System is used. These logical names also allow independence from

knowing the physical location of a host. A host may be moved to a different network,

while the users continue to use the same logical name. The Domain Name System (DNS)

is a distributed database used by TCP/IP applications to map between hostnames and IP

addresses, and to provide electronic mail routing information. Each site (university

department, campus,company, or department within a company, for example) maintains

its own database of information and runs a server program that other systems across the

Internet can query. The DNS provides the protocol which allows clients and servers to

communicate with each other.

The system accesses the DNS through a resolver. The resolver gets the hostname

and returns the IP address or gets an IP address and looks up a hostname. The resolver

returns the IP address before asking the TCP to open a connection or sending a datagram

using UDP.

DNS Organization

The domain name system uses a hierarchical naming scheme known as domain

names,which is similar to the Unix filesystem tree. The root of the DNS tree is a special

node with a null label. The name of each node (except root) has to be up to 63

characters.The domain name of any node in the tree is the list of labels, starting at that

node, working up to the root, using a period (”dot”) to separate the labels (individual

sections of a name might represent sites or a group, but the domain system simply calls

each section a label ). The difference between the Unix filesystem and the tree of the

DNS is that in the DNS we start on the ground and “go up” till the root. Writing them in

this order makes it possible to compress messages that contain multiple domain names.

Thus, the domain name “tau.ac.il” contains three labels: “tau”, “ac”, and “il”. Any suffix

of a label in a domain name is also called a domain. In the above example the lowest

level domain is “tau.ac.il” (the domain name for the Tel-Aviv University Academic

organization in Israel), the second level domain is “ac.il” (the domain name for Academic

organizations of Israel), and the top level domain (for this name) is “il” (the domain name

for Israel). The node il is the second level node (after root).

Every node in the tree must have a unique domain name, but the same label can be

used at different points in the tree. The top-level domains are divided into three areas:

1. arpa is a special domain used for address-to-name mapping.

2. The seven 3-character domain names ( generic (organizational) domains).

3. The 2-character domains are based on the country codes. These are called the country

(the geographical) domains.

The seven generic domains are as listed above.

The Internet scheme can accomodate a wide variety of organizations, and allows

each group to choose between geographical or organizational naming hierarchies. Most

sites follow the Internet scheme so they can attach their TCP/IP installations to the

connected Internet without changing names. The zone is a subtree of the DNS that is

administered separately. A common zone is a second-level domain, “ac.il” for example.

Thus a lot of second-level domains divide their zone into smaller zones.

Whenever a new system is installed in a zone, the DNS administrator for the zone

allocates a name and an IP address for the new system and enters these into the name

server’s database. A name server is said to have authority forone zone or multiple zones.

Often, server software executes on a dedicated processor, and this computing machine is

called the name Server.

The person responsible for a zone must provide a primary name server for that

zone and one or more second

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