The document provides an overview of the Domain Name System (DNS). It discusses how DNS works to translate domain names to IP addresses by using a distributed database across multiple server types. DNS implements a hierarchical namespace and resolves domain names through cooperation between local name servers and authoritative name servers. It allows internet resources to be accessed through easy to remember domain names instead of hard to remember IP addresses.

1. GL
BAL
Institute of Information Technology

2. A Presentation on
Domain Name System
Group Name :-
G2
Group Members :- Gaurav Kumar
Rohitash kumar
Nitesh Kumar
Rahul Baghla

3.  Key terms
 What is internet
 How do they connect
 History of the DNS
 Introduction to the DNS
 Components of the DNS
 The namespace
 The servers
 The resolvers
 Conclusion

4.  The internet is a global system of interconnected
computer networks . It is a network of networks that
consists of millions of private and public , academic ,
business and government networks of local to global
space that are linked by transmission media such as
copper wires , fiber optic cables , wireless connections
and other technologies .

5.  A network of computers connected to each other
is called internet and these computers needed to
know which computer they were connecting to, so
each computer was given a unique number – an IP
(Internet Protocol) number. E.g. 121.245.078.2

6.  There was the ARPANET’s HOSTS.TXT file
 Each computer on the network retrieved a file called HOSTS.TXT
 HOSTS.TXT mapped every ARPANET host’s name to its IP address.
 The HOSTS.TXT file mapped numerical addresses to names.
 Allows users to specify an IP address (e.g. 192.0.34.166) to use for a
host name (e.g. www.google.com) without checking DNS.

Systems based on a hosts file have inherent limitations
 The obvious requirement that every time a given computer's address
changed, every computer that seeks to communicate with it would
need an update to its hosts file.

7.  Consistency
 The network changed more quickly than the file was updated
 Name collisions
 No two hosts could have the same name
 “Good” names quickly exhausted
 There was no good method to prevent duplicate names
 Human intervention was required
 Traffic and load
 The traffic generated by downloading the file became
significant
 Download time sometimes longer than update period
 The model didn't scale well

8.  ARPANET powers-that-were launched an investigation into
replacement for HOSTS.TXT
 Requirements:
 Decentralized administration
 With data updated locally, but available globally
 A hierarchical name space
 To guarantee unique names
 Paul V. Mockapetris, American computer scientist and
Internet pioneer, together with Jon Postel, invented the
Internet Domain Name System (DNS).

9.  The domain name system is usually used to translate a
host name into an IP address and vice versa.
 Domain names comprise a hierarchy so that names are
unique, yet easy to remember.
 DNS implements a distributed database to store
domain name and address information for all public
hosts on the Internet.
 Defines a hierarchical namespace where each level
of the namespace is separated by a “.”

10. A fully qualified domain name is processed from right
to left for its translation into the corresponding IP address. A
fully qualified domain name can be made up of a top level
domain (TLD), second level domain (SLD) and sub domains

11.  The Name Space
 The Servers
 The Resolver

12.  The name space is the structure of the DNS database
 An inverted tree with the root node at the top
 Each node has a label
The root node
""
top-level node
second-level node
third-level node
top-level node
second-level node
second-level node
third-level node
top-level node
second-level node
third-level node
second-level node

13.  A domain name is the sequence of labels from a node to the
root, separated by dots (“ . ”), read left to right

15. in

17.  One domain is a subdomain of another if its apex
node is a descendant of the other’s apex node
 More simply, one domain is a subdomain of
another if its domain name ends in the other’s
domain name
 So abc.webs.com is a subdomain of
 webs.com
 com
 webs.com is a subdomain of com

18.  The Name Space
 The Servers
 The Resolver

19.  Name servers store information about the name
space in units called “zones”
 The name servers that load a complete zone are said to
“have authority for” or “be authoritative for” the zone
 Usually, more than one name server are
authoritative for the same zone
 This ensures redundancy and spreads the load
 Also, a single name server may be authoritative for
many zones

20. Two main types of servers
 Local name servers:

Each ISP, company has local (default) name server

Host DNS query first goes to local name server
 Authoritative name server:

For a host: stores that host’s IP address, name

Can perform name/address translation for that host’s name

21.  Contacted by local name server that can not resolve name
 Root name server:
 contacts authoritative name server if name mapping not
known
 Gets mapping & returns mapping to local name server

22.  The Name Space
 The Servers
 The Resolver

23.  Name resolution is the process by which client and
Local name servers cooperate to find data in the
name space.
 A Local name server receives a query from a client ,
looks for the answer in its database
 If the answer isn’t in the database and the server isn’t
authoritative for the answer, the answer must be
looked up.

24.  Let’s look at the resolution process step-by-step:
Client Computer
www.google.com

25.  The client computers asks its Local name server,
for www.google.com’s address
Local Name Server
What’s the IP address
of www.google.com?
Client Computer
www.google.com

26.  The Local name server asks a Root name server , for
www.google.com’s address
Local Name Server
What’s the IP address
of www.google.com?
Client Computer
www.google.com
Root Server

27.  The root server refers Local name server to the .com
name servers.
Local Name Server
Client Computer
www.google.com
Root Server
Here’s a list of the
.com name servers.
Ask one of them.

28.  The Local name server asks .com name server,
for www.google.com’s address
What’s the IP address
of www.google.com?
Root Server
Local Name Server
.com Server
Client Computer
www.google.com

29.  The com name server refers Local name server
to the google.com name servers
Here’s a list of the
google.com name
servers. Ask one
of them.
Root Server
Local Name Server
.com Server
Client Computer
www.google.com

30.  The Local name server asks google.com name server,
for www.google.com’s address
What’s the IP address
of www.google.com?
Root Server
Local Name Server
Google.com Server
.com Server
Client Computer
www.google.com

31.  The google.com name server responds with
www.google.com’s address
Root Server
Local Name Server
Here’s the IP
address for
www.google.com
Google.com Server
.com Server
Client Computer
www.google.com

32.  The Local name server responds to client
computer with www.google.com’s address
Here’s the IP
address for
www.google.com
Root Server
Local Name Server
Google.com Server
.com Server
Client Computer
www.google.com

33.  After the previous query, the Local name server now knows:
 The names and IP addresses of the com name servers
 The names and IP addresses of the google.com name servers
 The IP address of www.google.com
 Let’s look at the resolution process again
Client Computer
www.google.com

34.  The client computer asks its Local name server,
for www.google.com’s address
Root Server
Local Name Server
What’s the IP address
of google.com?
Google.com Server
.com Server
Client Computer
www.google.com

35.  The Local name server responds to client computer
with www.google.com’s address
Here’s the IP
address for
google.com
Root Server
Local Name Server
Google.com Server
.com Server
Client Computer
www.google.com

36.  DNS is like a phone book for the Internet. If we know a
person’s name but don’t know his mobile number, we
can simply look it up in a phone book. DNS provides
this same service to the Internet.
 When we visit www.google.com in a browser, our
computer uses DNS to retrieve the website’s IP address
of 173.194.69.147 .