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 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.
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