Domain name system

BALGLInstitute of Information Technology

A Presentation on Domain Name System

Gaurav KumarRohitash kumarNitesh KumarRahul Baghla

Group Members :-

Group Name :- G2

Key terms What is internet How do they connect

History of the DNS Introduction to the DNSComponents of the DNS

The namespace The servers The resolvers

Conclusion

Contents :-

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 .

What is the internet?

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

How do they Connect?

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.TXTConsistency

The network changed more quickly than the file was updated

Name collisionsNo two hosts could have the same name

“Good” names quickly exhaustedThere was no good method to prevent duplicate

namesHuman intervention was required

Traffic and loadThe traffic generated by downloading the file

became significantDownload time sometimes longer than update period

The model didn't scale well

Solving the ProblemARPANET powers-that-were launched an

investigation into replacement for HOSTS.TXT

Requirements:Decentralized administration

With data updated locally, but available globallyA 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).

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 “.”

Domain Name System ?

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

Continued…

Components of the DNS :-

The Name Space

The Servers

The Resolver

The Name SpaceThe 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""

Domain NamesA domain name is the sequence of labels from a

node to the root, separated by dots (“ . ”), read left to right

in

SubdomainsOne 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 nameSo abc.webs.com is a subdomain of

webs.comcom

webs.com is a subdomain of com


The Name Space

The Servers

The Resolver

Name ServersName 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 zoneThis 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

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

Root Name Server


The Name Space

The Servers

The Resolver

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 ProcessThe client computers asks its Local name

server, for www.google.com’s address

www.google.com

Local Name Server

Client Computer

The Resolution ProcessThe Local name server asks a Root name

server , for www.google.com’s address

www.google.com

Root ServerLocal Name Server


Client Computer

The Resolution ProcessThe 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 ProcessThe Local name server asks .com name


www.google.com



.com Server

Client Computer

The Resolution ProcessThe com name server refers Local name

server to the google.com name servers

www.google.com

.com Server


Here’s a list of the google.com name servers. Ask one

of them.

Client Computer

The Resolution ProcessThe Local name server asks google.com name


www.google.com

.com Server


Google.com Server


Client Computer

The Resolution ProcessThe google.com name server responds

with www.google.com’s address

www.google.com

.com 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 ProcessThe Local name server responds to

client computer with www.google.com’s address

www.google.com

.com 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

serversThe names and IP addresses of the google.com

name serversThe 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


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


Google.com Server

Client Computer

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 .

Conclusion

Education

Domain name system