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presentation on DNS
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BALGLInstitute of Information Technology
A Presentation on Domain Name System
Gaurav KumarSahil Sardana
Group Members :-
Group Name :- G2
Contents :-
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
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 .
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
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 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.
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 namesHuman intervention was
required Traffic and load
The traffic generated by downloading the file became significantDownload time sometimes
longer than update period The model didn't scale well
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 spaceTo guarantee unique names
Paul V. Mockapetris, American computer scientist and Internet pioneer, together with Jon Postel, invented the Internet Domain Name System (DNS).
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 “.”
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
Domain Names A domain name is the sequence of labels from a
node to the root, separated by dots (“ . ”), read left to right
in
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
ofwebs.comcom
webs.com is a subdomain of com
Components of the DNS :-
The Name Space
The Servers
The Resolver
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
th ird -le ve l n o de
se co n d-le ve l no de se co n d-le ve l no de
to p -le ve l no de
th ird -le ve l n o de th ird -le ve l n o de
se co n d-le ve l no de
to p -le ve l no de
se co n d-le ve l no de se co n d-le ve l no de
to p -le ve l no de
T h e roo t no de""
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
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
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
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.
www.google.com
The Resolution Process
Let’s look at the resolution process step-by-step:
Client Computer
What’s the IP address of www.google.com?
The Resolution Process
The client computers asks its Local name server, for www.google.com’s address
www.google.com
Local Name Server
Client Computer
The Resolution Process
The Local name server asks a Root name server , for www.google.com’s address
www.google.com
Root ServerLocal Name Server
What’s the IP address of www.google.com?
Client Computer
The Resolution Process
The root server refers Local name server to the .com name servers.
www.google.com
Root ServerLocal Name ServerHere’s a list of the .com name
servers. Ask one of them.
Client Computer
The Resolution Process
The Local name server asks .com name server, for www.google.com’s address
www.google.com
Root ServerLocal Name Server
What’s the IP address of www.google.com?
.com Server
Client Computer
The Resolution Process
The com name server refers Local name server to the google.com name servers
www.google.com
.com Server
Root ServerLocal Name Server
Here’s a list of the google.com name servers. Ask one
of them.
Client Computer
The Resolution Process
The Local name server asks google.com name server, for www.google.com’s address
www.google.com
.com Server
Root ServerLocal Name Server
Google.com Server
What’s the IP address of www.google.com?
Client Computer
The Resolution Process
The google.com name server responds with www.google.com’s address
www.google.com
.com Server
Root ServerLocal Name Server
Google.com ServerHere’s the IP address for
www.google.com
Client Computer
Here’s the IP address for
www.google.com
The Resolution Process
The Local name server responds to client computer with www.google.com’s address
www.google.com
.com Server
Root ServerLocal Name Server
Google.com Server
Client Computer
www.google.com
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 google.com
name servers The IP address of www.google.com
Let’s look at the resolution process again
Client Computer
www.google.com
What’s the IP address of google.com?
Resolution Process (Caching)
The client computer asks its Local name server, for www.google.com’s address
.com Server
Root ServerLocal Name Server
Google.com Server
Client Computer
www.google.com
Here’s the IP address for google.com
Resolution Process (Caching)
The Local name server responds to client computer with www.google.com’s address
.com Server
Root ServerLocal Name Server
Google.com Server
Client Computer
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 .