2. A Presentation on
Domain Name System
Group Name :-
G2
Group Members :- Gaurav Kumar
Rohitash kumar
Nitesh Kumar
Rahul Baghla
3. ï Key terms
ï What is internet
ï How do they connect
ï History of the DNS
ï Introduction to the DNS
ï Components of the DNS
ï The namespace
ï The servers
ï The resolvers
ï Conclusion
4. ï 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. ï 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 â an IP
(Internet Protocol) number. E.g. 121.245.078.2
6. ï There was the ARPANETâs HOSTS.TXT file
ï Each computer on the network retrieved a file called HOSTS.TXT
ï HOSTS.TXT mapped every ARPANET hostâs name to its IP address.
ï The HOSTS.TXT file mapped numerical addresses to names.
ï 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.
ï
Systems based on a hosts file have inherent limitations
ï 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. ï Consistency
ï The network changed more quickly than the file was updated
ï Name collisions
ï No two hosts could have the same name
ï âGoodâ names quickly exhausted
ï There was no good method to prevent duplicate names
ï Human intervention was required
ï Traffic and load
ï The traffic generated by downloading the file became
significant
ï Download time sometimes longer than update period
ï The model didn't scale well
8. ï ARPANET powers-that-were launched an investigation into
replacement for HOSTS.TXT
ï Requirements:
ï Decentralized administration
ï With data updated locally, but available globally
ï A hierarchical name space
ï To guarantee unique names
ï Paul V. Mockapetris, American computer scientist and
Internet pioneer, together with Jon Postel, invented the
Internet Domain Name System (DNS).
9. ï The domain name system is usually used to translate a
host name into an IP address and vice versa.
ï Domain names comprise a hierarchy so that names are
unique, yet easy to remember.
ï DNS implements a distributed database to store
domain name and address information for all public
hosts on the Internet.
ï Defines a hierarchical namespace where each level
of the namespace is separated by a â.â
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
11. ï The Name Space
ï The Servers
ï The Resolver
12. ï The name space is the structure of the DNS database
ï An inverted tree with the root node at the top
ï 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. ï A domain name is the sequence of labels from a node to the
root, separated by dots (â . â), read left to right
17. ï One domain is a subdomain of another if its apex
node is a descendant of the otherâs apex node
ï More simply, one domain is a subdomain of
another if its domain name ends in the otherâs
domain name
ï So abc.webs.com is a subdomain of
ï webs.com
ï com
ï webs.com is a subdomain of com
18. ï The Name Space
ï The Servers
ï The Resolver
19. ï Name servers store information about the name
space in units called âzonesâ
ï The name servers that load a complete zone are said to
âhave authority forâ or âbe authoritative forâ the zone
ï Usually, more than one name server are
authoritative for the same zone
ï This ensures redundancy and spreads the load
ï Also, a single name server may be authoritative for
many zones
20. Two main types of servers
ï Local name servers:
ï§
Each ISP, company has local (default) name server
ï§
Host DNS query first goes to local name server
ï Authoritative name server:
ï§
For a host: stores that hostâs IP address, name
ï§
Can perform name/address translation for that hostâs name
21. ï Contacted by local name server that can not resolve name
ï Root name server:
ï§ contacts authoritative name server if name mapping not
known
ï§ Gets mapping & returns mapping to local name server
22. ï The Name Space
ï The Servers
ï The Resolver
23. ï Name resolution is the process by which client and
Local name servers cooperate to find data in the
name space.
ï A Local name server receives a query from a client ,
looks for the answer in its database
ï If the answer isnât in the database and the server isnât
authoritative for the answer, the answer must be
looked up.
24. ï Letâs look at the resolution process step-by-step:
Client Computer
www.google.com
25. ï The client computers asks its Local name server,
for www.google.comâs address
Local Name Server
Whatâs the IP address
of www.google.com?
Client Computer
www.google.com
26. ï The Local name server asks a Root name server , for
www.google.comâs address
Local Name Server
Whatâs the IP address
of www.google.com?
Client Computer
www.google.com
Root Server
27. ï The root server refers Local name server to the .com
name servers.
Local Name Server
Client Computer
www.google.com
Root Server
Hereâs a list of the
.com name servers.
Ask one of them.
28. ï The Local name server asks .com name server,
for www.google.comâs address
Whatâs the IP address
of www.google.com?
Root Server
Local Name Server
.com Server
Client Computer
www.google.com
29. ï The com name server refers Local name server
to the google.com name servers
Hereâs 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. ï The Local name server asks google.com name server,
for www.google.comâs address
Whatâs the IP address
of www.google.com?
Root Server
Local Name Server
Google.com Server
.com Server
Client Computer
www.google.com
31. ï The google.com name server responds with
www.google.comâs address
Root Server
Local Name Server
Hereâs the IP
address for
www.google.com
Google.com Server
.com Server
Client Computer
www.google.com
32. ï The Local name server responds to client
computer with www.google.comâs address
Hereâs the IP
address for
www.google.com
Root Server
Local Name Server
Google.com Server
.com Server
Client Computer
www.google.com
33. ï After the previous query, the Local name server now knows:
ï The names and IP addresses of the com name servers
ï The names and IP addresses of the google.com name servers
ï The IP address of www.google.com
ï Letâs look at the resolution process again
Client Computer
www.google.com
34. ï The client computer asks its Local name server,
for www.google.comâs address
Root Server
Local Name Server
Whatâs the IP address
of google.com?
Google.com Server
.com Server
Client Computer
www.google.com
35. ï The Local name server responds to client computer
with www.google.comâs address
Hereâs the IP
address for
google.com
Root Server
Local Name Server
Google.com Server
.com Server
Client Computer
www.google.com
36. ï DNS is like a phone book for the Internet. If we know a
personâs name but donât know his mobile number, we
can simply look it up in a phone book. DNS provides
this same service to the Internet.
ï When we visit www.google.com in a browser, our
computer uses DNS to retrieve the websiteâs IP address
of 173.194.69.147 .