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
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
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
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
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 .