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 .