1. Presented By:
Diwaker pant
ME (ECE) Regular

2.  DNS- Definition
 Name Space
◦ Flat Name Space
◦ Hierarchical Name Space
 Domain Name Space
◦ FULLY QUALIFIED DOMAIN NAME(FQDN)
◦ PARTIALLY QUALIFIED DOMAIN NAME(PQDN)
 Distribution of Name Space
◦ Hierarchy of Name servers
◦ Zone and Domains
◦ Root, Primary and Secondary Servers
 DNS in Internet
◦ Generic , Country and Inverse Domain
 Resolution
 DNS messages
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3.  To identify an entity, TCP/IP uses IP addresses which
uniquely identifies connection of host to internet.
 We prefer to use names instead of numeric addresses .
 So we need a system that can map a name to a numeric
address and vice versa. This is called DOMAIN NAME
SYSTEM
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4.  When internet was small, mapping was done using
HOST FILE which was stored on every host.
 Host file had only two columns: name and address.
 But now a days whole information is divided into
smaller parts and each part is stored in different
computer. This is called DNS.
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5.  The process of mapping a unique name with the unique
IP address.
 FLAT NAME SPACE –
 A name is assigned to an address and name is a
sequence of characters without structure.
 It can not be used in large system such as Internet.
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6.  HIERARCHICAL NAME SPACE-
 Each name is made of several parts.
 The first part can define the nature of organization.
 Second part can define the name and third can define
the departments in organization.
 For example
o Smart.pu.edu
o Smart.nitttr.edu
o smart.unix.com
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7.  To have a hierarchical name space, a DOMAIN NAME
SPACE was designed.
 In this design the names are defined in an inverted tree
structure with the root at top.
 The tree can have only 128 levels i.e. level 0(root) to
level 127.
 Tree consists of nodes and each node has a LABEL.
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8.  Label is a string with a max. of 63 characters.
 The root label is a null string.
 Siblings have different labels to maintain uniqueness.
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9.  Each node in the tree has a domain name.
 Full domain name is sequence of labels separated by
dots(.)
 Domain name is read from node up to root.
 Always ends in a null label i.e. last character is a dot.
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10. DNS By Diwaker Pant October 9, 2012 10

11.  FULLY QUALIFIED DOMAIN NAME(FQDN)
 It contains the full name of host.
 A label is terminated by a null string.
 PARTIALLY QUALIFIED DOMAIN NAME(PQDN)
 It starts from a node but doesn’t reaches root.
 A label is not terminated by null string.
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12.  Domain is a sub
tree of domain
name space.
 Each domain can
be divided into
sub domains.
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13. DNS By Diwaker Pant October 9, 2012 13

14.  Region over which server
has the responsibility and
authority.
 Zone is a part of entire
tree.
 Server can divide domain
into smaller domains.
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15.  ROOT SERVER-It is a server whose zone consist of
whole tree. These servers are distributed all around the
world.
 PRIMARY SERVER- A primary server loads all
information from the local disk file.
 SECONDARY SERVER- It transfer the complete
information from the primary server and it is called
Zone transfer.
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16.  DNS is a protocol can be used in different platforms.
 In the internet, DNS tree is divided into three different sections
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17.  It contains registered hosts according to generic behaviors.
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18. Label Description
com Commercial organizations
edu Educational institutions
gov Government institutions
int International organizations
mil Military groups
net Network support centers
org Nonprofit organizations
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19. Label Description
aero Airlines and aerospace companies
biz Businesses or firms (similar to com)
coop Cooperative business organizations
info Information service providers
museum Museums and other nonprofit organizations
name Personal names (individuals)
pro Professional individual organizations
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20. Two characters country abbreviations.
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21.  Use to map an address to a
name.
 When a server received a
request from a client to do a
task.
 Inverse or pointer (PTR)
query.
 121.45.34.132.in-addr.arpa
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22.  Mapping a name to an address or an address to a name is
called name –address resolution.
 RESOLVER-It access the closest DNS server with a
mapping request. If the server has the information, it
satisfies the resolver ; otherwise refers the resolver to
other servers or asks the other servers to provide the
information.
 MAPPING NAMES TO ADDRESSES-
Resolver gives domain name to the server and ask for
address. It uses country and generic domain to find the
mapping.
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23.  MAPPING ADDRESS TO NAMES.
 Resolver sends IP address to the server to be mapped
to domain name.
 This is called PTR or Inverse query.
 Server uses inverse domain.
IP address -121.45.34.132
Domain name-132.34.45.121.in-addr.arpa.
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24. RECURSIVE RESOLUTION
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25.  ITERATIVE RESOLUTION
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26.  CACHING
 When a server asks for mapping from another server and
receive the response, it stores the information an its cache
memory before sending it to the clients.
 If the same or other client ask for the same mapping, it can
check its cache memory and resolve the problem.
 But this type of response is always marked as
unauthoritative.
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27.  Query and response
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28. DNS By Diwaker Pant October 9, 2012 28

29.  In DNS , when there is a change , such as adding a new
host, removing a host or changing an IP address,
change must be made to the DNS master file.
 Manual updating is not possible due to size of Internet.
 It is use to update DNS master file automatically.
 Information in both primary and secondary servers is
changed.
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30.  DNS can use either UDP or TCP.
 PORT NO. 53 is used by servers.
 If size of response message is more than 512 bytes,
TCP connection is used, otherwise UDP is used.
 How are the new domains added to the server.
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31.  This is done through a registrar, a commercial entity
accredited by ICANN (Internet corporation for
assigned name and numbers).
 Name is added to the DNS database after verification
by Registrar for uniqueness of the name.
 A fee is charged.
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32.  The domain name system is a client /server application
that identifies each host on the internet with a unique
friendly name.
 Its structure is an inverted hierarchical tree structure.
 Each node in the tree has a domain name.
 Generic domain , Country domain, Inverse domain.
 DDNS automatically updates the DNS master.
 DNS use the service UDP for message of less than 512
bytes .otherwise, TCP is used.
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33.  Behrouz A. Forouzan - Data Communication and
Networking (3rd ,4th edition)
 Andrew S. Tanenbaum - Computer Networks (4th
edition)
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34. DNS By Diwaker Pant October 9, 2012 34

35. The client (resolver) can ask for the answer from a name server,
generally closet DN server.
If the server is the authority for the domain name it will responds
back with the full answer after checking its database, but if the closet
server is not the authority then it will pass query to next closet server
generally parent.
Then this server will again check its database and responds back with
answer if it is authority, otherwise it will pass the query to next
server…
This process will repeats until the authoritative server gives final
answer.
When the query is finally resolved. The response travels back to
requesting client.
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36. If the clients does not ask for the recursive answer, the mapping can
be done iteratively.
If the server is an authority for the name, it sends the answer.
If it is not then it returns (to the clients) the IP add of the server that it
thinks can resolve the problem.
The client is responsible for repeating the query to new server.
If this new server can resolve the query then it will responds back
with the Final IP address as an answer otherwise it returns the IP
address of the new server.
This process is called Iterative because The client repeats the query to
multiple servers.
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