2. A Presentation on
Domain Name System
Group Name :-
G2
Group Members :- Gaurav Kumar
Sahil Sardana
3. Contents :
Key terms
What is internet
How do they connect
History of the DNS
Introduction to the DNS
Components of the DNS
The servers
The namespace
The resolvers
Conclusion
4. What is the internet?
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. How do they Connect?
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. In the Beginning...
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
7. The Problems with
HOSTS.TXT
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
8. Solving the Problem
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
9. Domain Name System ?
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. Continued…
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. Domain Names
A domain name is the sequence of labels from a node
to the root, separated by dots (“ . ”), read left to right
15. Subdomains
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
16.
17. Components of the DNS :
The Name Space
The Servers
The Resolver
18. The Name Space
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
19. Name Servers
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. Types of Name Servers :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. Root Name Server
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. Name Resolution
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. The Resolution Process
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
25. The Resolution Process
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
26. The Resolution Process
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.
27. The Resolution Process
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
28. The Resolution Process
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
29. The Resolution Process
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
30. The Resolution Process
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
31. The Resolution Process
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
32. Resolution Process (Caching)
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
servers
The
google.com
IP address of www.google.com
Let’s look at the resolution process again
Client Computer
www.google.com
name
33. Resolution Process (Caching)
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
34. Resolution Process (Caching)
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
35. Conclusion
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 .
