domain name system
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TRANSCRIPT
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
Components of the DNS :-
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
Components of the DNS :-
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
What’s the IP address of www.google.com?
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
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 ProcessThe 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 ProcessThe 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 ProcessThe 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 ProcessThe 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
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
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
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