DNS Domain Name System DNS Domain Name System Notes | EduRev

: DNS Domain Name System DNS Domain Name System Notes | EduRev

 Page 1


DNS Domain Name System 
 
 
Page 2


DNS Domain Name System 
 
 
Domain names and IP addresses 
• People prefer to use easy-to-remember names instead of IP 
addresses  
 
• Domain names are alphanumeric names for IP addresses 
e.g., neon.ece.utoronto.ca, www.google.com, ietf.org 
• The domain name system (DNS) is an Internet-wide 
distributed database that translates between domain names 
and  IP addresses 
 
• How important is DNS?  
 Imagine what happens when the local DNS server is down. 
Page 3


DNS Domain Name System 
 
 
Domain names and IP addresses 
• People prefer to use easy-to-remember names instead of IP 
addresses  
 
• Domain names are alphanumeric names for IP addresses 
e.g., neon.ece.utoronto.ca, www.google.com, ietf.org 
• The domain name system (DNS) is an Internet-wide 
distributed database that translates between domain names 
and  IP addresses 
 
• How important is DNS?  
 Imagine what happens when the local DNS server is down. 
Before there was DNS …. 
…. there was the HOSTS.TXT file 
 
• Before DNS (until 1985), the name-to-IP address was done 
by downloading a single file (hosts.txt) from a central server 
with FTP.  
– Names in hosts.txt are not structured. 
– The hosts.txt file still works on most operating systems. It 
can be used to define local names. 
 
 
 
Page 4


DNS Domain Name System 
 
 
Domain names and IP addresses 
• People prefer to use easy-to-remember names instead of IP 
addresses  
 
• Domain names are alphanumeric names for IP addresses 
e.g., neon.ece.utoronto.ca, www.google.com, ietf.org 
• The domain name system (DNS) is an Internet-wide 
distributed database that translates between domain names 
and  IP addresses 
 
• How important is DNS?  
 Imagine what happens when the local DNS server is down. 
Before there was DNS …. 
…. there was the HOSTS.TXT file 
 
• Before DNS (until 1985), the name-to-IP address was done 
by downloading a single file (hosts.txt) from a central server 
with FTP.  
– Names in hosts.txt are not structured. 
– The hosts.txt file still works on most operating systems. It 
can be used to define local names. 
 
 
 
Resolver and name server 
1. An application program on a host 
accesses the domain system 
through a DNS client, called the 
resolver 
2. Resolver contacts DNS server, 
called name server  
3. DNS server returns IP address to 
resolver which passes the IP 
address to application 
 
 
• Reverse lookups are also 
possible, i.e., find the hostname 
given an IP address 
HTTP Resolver
Hostname (neon.tcpip-lab.edu)
IP address (128.143.71.21)
Name 
server
Hostname 
(neon.tcpip-lab.edu)
IP address (128.143.71.21)
Page 5


DNS Domain Name System 
 
 
Domain names and IP addresses 
• People prefer to use easy-to-remember names instead of IP 
addresses  
 
• Domain names are alphanumeric names for IP addresses 
e.g., neon.ece.utoronto.ca, www.google.com, ietf.org 
• The domain name system (DNS) is an Internet-wide 
distributed database that translates between domain names 
and  IP addresses 
 
• How important is DNS?  
 Imagine what happens when the local DNS server is down. 
Before there was DNS …. 
…. there was the HOSTS.TXT file 
 
• Before DNS (until 1985), the name-to-IP address was done 
by downloading a single file (hosts.txt) from a central server 
with FTP.  
– Names in hosts.txt are not structured. 
– The hosts.txt file still works on most operating systems. It 
can be used to define local names. 
 
 
 
Resolver and name server 
1. An application program on a host 
accesses the domain system 
through a DNS client, called the 
resolver 
2. Resolver contacts DNS server, 
called name server  
3. DNS server returns IP address to 
resolver which passes the IP 
address to application 
 
 
• Reverse lookups are also 
possible, i.e., find the hostname 
given an IP address 
HTTP Resolver
Hostname (neon.tcpip-lab.edu)
IP address (128.143.71.21)
Name 
server
Hostname 
(neon.tcpip-lab.edu)
IP address (128.143.71.21)
Design principle of DNS 
• The naming system on which DNS is based is a hierarchical and logical 
tree structure called the domain namespace.  
 
• An organization obtains authority for parts of the name space, and can add 
additional layers of the hierarchy 
 
• Names of hosts can be assigned without regard  of location on a link layer 
network, IP network or autonomous system  
 
• In practice, allocation of the domain names generally follows the allocation 
of IP address, e.g.,  
– All hosts with network prefix 128.143/16 have domain name suffix 
virginia.edu 
– All hosts on network 128.143.136/24 are in the Computer Science 
Department of the University of Virginia 
Read More
Offer running on EduRev: Apply code STAYHOME200 to get INR 200 off on our premium plan EduRev Infinity!