Dns

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 .