Domain Name System Architecture

Domain Name System Architecture:

Ø  The Domain name system comprises of Domain Names, Domain Name Space, Name Server that have been described below:

a)    Domain Names:

 

Ø  Domain Name is a symbolic string associated with an IP address.

Ø  Each node in the tree has a domain name.

Ø  A full domain name is a sequence of labels separated by dots (.).

Ø  The domain names are always read from the node up to the root.

Ø  The last label is the label of the root (null). This means that a full domain name always ends in a null label, which means the last character is a dot because the null string is nothing. 

Fully Qualified Domain Name

Ø  If a label is terminated by a null string [null means nothing, the label ends with a dot (.) ] , it is called a fully qualified domain name.(FQDN).

Ø  An FQDN is a domain name that contains the full name of a host.

Ø  It contains all labels, from the most specific to the most general, that uniquely define the name of the host. For example, the domain name

challenger.ate.tbda.edu.

Partially Qualified Domain Name

Ø  If a label is not terminated by a null string, it is called a partially qualified domain name (PQDN).

Ø  A PQDN starts from a node, but it does not reach the root.

Ø  It is used when the name to be resolved belongs to the same site as the client.

Ø  There are several domain names available; some of them are generic such as .com, .edu, .gov, .net etc, while some country level domain names such as .au, .in, .za , .us etc.

Ø  The following table shows the Generic Top-Level Domain names:

Domain Name	Meaning
Com	Commercial business
Edu	Education
Gov	U.S. government agency
Int	International entity
Mil	U.S. military
Net	Networking organization
Org	Non profit organization

Ø  The following table shows the Country top-level domain names:

Domain Name	Meaning
au	Australia
in	India
cl	Chile
fr	France
us	United States
za	South Africa
uk	United Kingdom
jp	Japan
es	Spain
de	Germany
ca	Canada
ee	Estonia
hk	Hong Kong

b)   Domain Name Space

Ø  The domain name space refers a hierarchy in the internet naming structure.

Ø  This hierarchy has multiple levels (from 0 to 127), with a root at the top.

Ø  The following diagram shows the domain name space hierarchy:

Ø  In the above diagram each sub-tree represents a domain. Each domain can be partitioned into sub domains and these can be further partitioned and so on.

c)   Name Server

Ø  Name server contains the DNS database.

Ø  This database comprises of various names and their corresponding IP addresses.

Ø  Since it is not possible for a single server to maintain entire DNS database,

Ø  Therefore, the information is distributed among many DNS servers.

Ø  Hierarchy of server is same as hierarchy of names.

Ø  The entire name space is divided into the zones

            i.  Zones

Ø  Zone is collection of nodes (sub domains) under the main domain.

Ø  If the domain is not further divided into sub domains then domain and zone refers to the same thing.

Ø  The server maintains a database called zone file for every zone.

Ø  If the domain is further divided into sub domains then domain and zone refers to the different thing.

Ø  The information about the nodes in the sub domain is stored in the servers at the lower levels however; the original server keeps reference to these lower levels of servers.

Ø  Of course the original server does not free itself from responsibility totally: It still has a zone, but the detailed information is kept by the lower-level servers

TYPES OF NAME SERVERS:

Ø  Following are the three categories of Name Servers that manages the entire Domain Name System:

·   Root Server

·   Primary Server

·   Secondary Server

ROOT SERVER

Ø  Root Server is the top level server which consists of the entire DNS tree.

Ø  It does not contain the information about domains but delegates the authority to the other server

 PRIMARY SERVERS

Ø  Primary Server stores a file about its zone. It has authority to create, maintain, and update the zone file.

  SECONDARY SERVER

Ø  Secondary Server transfers complete information about a zone from another server which may be primary or secondary server.

Ø  The secondary server does not have authority to create or update a zone file.