Data Communication &networks: Domain Name System

Data communication &Networks
Lab
DNS(Domain Name System )
Hassan Bashir
Today’s Agenda/Topic:
-Internet Names and Addresses

-Domain name
-Structure of domain name
-Working of DNS
-Examples of DNS
-DNS TOOL
-DNS configuration using Packet Tracer
-Lab Task
Internet Names and Addresses
• If you want to…
• Call someone, you need to ask for their phone number
• Mail someone, you need to get their address first
• What about the Internet?
• If you need to reach Google, you need their IP
• Does anyone know Google’s IP?
• Problem:
• People can’t remember IP addresses
• Need human readable names that map to IPs
3
Internet Names and Addresses
• Addresses, e.g. 129.10.117.100
• Computer usable labels for machines
• Conform to structure of the network
• Names, e.g. www.usa.edu
• Human usable labels for machines
• Conform to organizational structure
• How do you map from one to the other?
• Domain Name System (DNS)
4
 Ad dr es ses a r e used to locate objects
 Names a r e easier to rememb er than numbers
 You would like to get to the a d d r e s s or other

objects using a name
 DNS provides a mapping from names to

r e s o u r c e s of several types
 Domain name is a way to identify and locate computers connected to internet
 No two organizations can have same domain name
 A domain name always consists of two or more components separated by

periods called dots (.)
EXAMPLE: www.yahoo.co.pk, www.facebook.com etc.
 Hostname . s eco n d - l ev el domain. t op- level domain
Top level domains a r e classified into 3 categories:
 Organizational or generic domains
 Geographical or country domains
 Rev ers e domains

 It consists of t h r e e character code which indicates the primary
function of the organization or their generic behavior
 Most commonly used top level domains are:
 .com for commercial organization eg www.y

 .net for networking organizations ahoo.com e g
 .gov for government organizations ewww.zedge.net
g
 .edu for educational organizations www.newjersey.gov
 .org for non-commercial organizations e g www.uducause.edu
eg www.eklavya.org
 .mil for military organizations e g www.dod.mil
 .int for international organizations e g www.itu.int
 It consists of two c h a ra c ter s which r e p r e s e n t s different
countries/regions all around the world
 T h e s e c o d e s have b e en standardized by International Standard
Organizational (ISO)
EXAMPLE:
 .pk Pakistan
 .jp japan
 .us United S tates
 .fr france
 .it Italy
 .cn China
 .au Australia
 Itis a special domain name in-addr.apra that is used
translate the IP a d d r es s to fully qualified domain name
EXAMPLE:
1.4.220.134 in-addr.apra will return sunc.scit.wlv. Her e
1.4.220.134 is the IP ad d r e s s that is mapped to its
name sunc.scit.wlv.at.uk with the help of in-addr.apra
domain.
 Each domain name has a corresponding IP a d d r es s
 When the u s e r t ypes the domain name in the a d d r es s bar,

the corresponding IP a d d r es s is supplied. Such a translation
is possible with the help of s y s t em called DNS (DOMAIN
NAME SYSTEM)
 DEFINITION:
“DOMAIN NAME SYSTEM is a collection of the d at ab ases

that contain information about domain names and their
corresponding IP address.”
 When an application program n e e d s to communicate with
other computer, it n e e d s to translate the name and the
other computer into its IP address. T h e applications
program that r eq u e s t s the service then b eco mes the client
of DNS.
 It then s e n d s the r equ es t to DNS ser v er. T h e s e r v e r looks

up the name and then returns cor rect IP address.
 A large number of DNS s e r v e r s may b e involved to get the

right IP address. After receiving the correct IP address, the
communication bet ween two computers starts.
root DNS
server
1. When you type name www.yahoo.com into your

browser it asks local DNS server (at ISP’s end) 2
3 com DNS
for its IP address.
server
4
2. When local DNS server does not find the IP
address of given name, it forwards request to
root DNS server and again enquire about IP
address of it. local DNS server
At ISP End
3. The root DNS server replies “ I do not know 1

the IP address of www.yahoo.com but know the
IP address of the com DNS server”.
Yahoo.com DNS server
4. The local DNS then asks the com DNS server
for IP address DNS client requesting for
www.yahoo.com
14
root DNS
server
5. The com DNS server replies with same

answer it does not know the IP address of 2
3 com DNS
www.yahoo.com but know the IP address of
server
yahoo.com DNS server which is then return to 4
local DNS server.
5
6. The local DNS server then ask the yahoo.com
local DNS server
DNS server for IP address At ISP End
6
7
7. It then replies with IP address corresponding 1 8
to www.yahoo.com which it has
8. The local DNS server then sends this IP Yahoo.com DNS server
address back to the client computer that send
the request DNS client requesting for
www.yahoo.com
DNS TOOLS
• There are several tools for monitoring DNS
information:
– whois –https://whois.domaintools.com tells you the
owner and primary DNS servers associated with a
domain (e.g. whois yahoo.com). Also available
via web browser at www.networksolutions.com
DNS TOOLS
• -nslookup and host (on UNIX machines) tell you IP address
information for a particular hostname on the internet (e.g.
-nslookup www.gmail.com or host www.nic.edu)
DNS TASKS
• What are IP addresses of the DNS
servers that contain information about
usa.edu.pk -
• What are the IP address of:
– www.google.com
– sandy.admin.tcs.com
– www.linux.org
DNS configuration using Packet Tracer

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Data communication &Networks

DNS(Domain Name System )

-Internet Names and Addresses

 Names a r e easier to rememb er than numbers

 You would like to get to the a d d r e s s or other

 DNS provides a mapping from names to

 No two organizations can have same domain name

 A domain name always consists of two or more components separated by

 Organizational or generic domains

 Geographical or country domains

 Rev ers e domains

 .com for commercial organization eg www.y

 When the u s e r t ypes the domain name in the a d d r es s bar,

“DOMAIN NAME SYSTEM is a collection of the d at ab ases

 It then s e n d s the r equ es t to DNS ser v er. T h e s e r v e r looks

 A large number of DNS s e r v e r s may b e involved to get the

1. When you type name www.yahoo.com into your

3. The root DNS server replies “ I do not know 1

5. The com DNS server replies with same

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