1. …… DNS……
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2.  What is DNS ?  Resolving
 Why DNS ?  Message format
 Working of DNS.  ER diagram
 DNS Hierarchy  DNS DB
 Features  Summary…
 Intro to IP
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3.  The term DNS stands for “domain name system.”
 DNS created in 1983 by Paul Mockapetris .
 A globally distributed, scalable, reliable, dynamic database
 It translates human-friendly website addresses into computer-friendly IP
addresses and viceversa.
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4.  the Internet is based on IP addresses, not domain names.
 IP Addresses are convinient for computers
(IP address includes information used for routing.)
 IP addresses are tough for humans to remember.
 IP addresses are impossible to guess.
 Domain names comprise a hierarchy so that names are unique, easy to
remember.
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5.  A domain is an arrangement of client and server computers that act together
as one system.
 A domain name is key to doing just about anything on the Internet, from
setting up a web site to sending and receiving email to building an online
store.
 A domain name is the sequence of labels from a node to the root, separated
by dots (“.”s), read left to right
 The name space has a maximum depth of 127 levels
 Domain names are limited to 255 characters in length
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6. Every interface on an internet must have a unique address called IP address.
These addresses are 32 –bit numbers, normally written as four decimal
numbers,one for each byte of the address.
This is called dotted-decimal notation.
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8.  Every machine has a unique identification in network. That will used to
identify the specific system in the network. That unique identifier is called
 The IP address is basically the address that distinguishes where you want
tosend information to, and from where the information comes.
 There simply has to be a way to distinguish with which of the millions of
computers in the world you want to communicate.
 The IP address is represented by the dotted values. Eg 172.16.35.254.
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9.  The IP(internet Protocol) is available in two versions,
 There are,
 IPv4(Internet Protocol version 4)
 IPv6(Internet Protocol version 6)
 IPv4 is wisely using internet protocol. Ipv6 is upgraded version of IPv4.
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10.  The IPv4 addresses are 4 byte(32 bits) in length.
 The IPv4 addresses denoted with the dotted numbers
 The IP address is denoted as “n.n.n.n”. Here „n‟ is a decimal value. The n
value range is 0 to 255.
 IPv4 is wisely using Internet Protocol.
 The IPv4 have the internet number as well as the host number.
 Eg:
 172.16.35.254
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11.  IPv6(Internet Protocol version 6) is a upgraded version of the IPv4.
 IPv6 addressing is denoted with the 8 sets of 4 hexadecimal values, 16 bits
in each sets. Each set is separated with the colon(:).
 IPv6 address is denoted as “xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx” (
‟x‟ would be hexadecimal value).
 The hexadecimal values can be represented in the Upper-case or Lower case
for the number „A-F‟. A leading zero in a set of numbers can be omitted
 ABC:567:0:8888:0:9999:1111:0
 abc:567:8888:0:9999:1111:0
 The IPv6 is not using wisely.
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12.  The DNS(Domain Name Server) is a directory lookup service that provides
a mapping between the name of the host on the internet and its numerical
address.
 Four elements comprise
 Domain Name Space
 DNS database
 Name servers
 Resolvers
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13.  It is 32 bit address provides uniquely identifying device.
 It has two components
 Network number
 Host address
 Domain refers to a group of hosts that are administrative control.
 Domains are organizes hierarchically, so that the domain has sub routines.
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14.  DNS is a hierarchical system.
 DNS organizes all registered names in a tree structure.
 At the base or root of the tree are a group of top-level domains including
familiar names like com, org, and edu.
 Below this level are the second-level registered domains such as about.com
 The tree can have 128 levels: level 0 (root) to level 127.
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17.  The DNS database contains a list of registered domain names.
 The top level of the DNS hierarchy, also called the root level
 It is maintained by a set of 13 servers called root name servers.
 Those servers in turn knows all the TLDs which contain the same vital
information
 They are coordinated by ICANN and are distributed around the world.
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19. ICANN
The Internet Corporation for Assigned
Names and Numbers
The headquarters is in Marina del Rey,
California, United States,
 It was created on September 18, 1998,and
incorporated on September 30, 1998.
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20.  To oversee administer Internet resources including
 Addresses
 Delegating blocks of addresses to the regional registries.
 Protocol identifiers
 Allocating port numbers, etc.
 Names
 Administration of the root zone file.
 Oversight of the operation of the root name servers.
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21. SCALABILITY
 No limit to the size of the database
 One server has over 20,000,000 names
Not a particularly good idea
 No limit to the number of queries
 24,000 queries per second handled easily
 Queries distributed among masters, slaves, and caches
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22. RELIABILITY
 Data is replicated
 Data from master is copied to multiple slaves
 Clients can query
 Master server
 Any of the copies at slave servers
 Clients will typically query local caches
 DNS protocols can use either UDP or TCP
 If UDP, DNS protocol handles retransmission, sequencing, etc.
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23. DYNAMICITY
 Database can be updated dynamically
 Add/delete/modify of any record
 Modification of the master database triggers replication
 Only master can be dynamically updated
Creates a single point of failure
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24. RESOLUTION
Mapping a name to an address or an address to a name is called name-
address resolution.
Types of Resolution:-
 Recursive Resolution
 Iterative Resolution
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25. Recursive resolution
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26. Iterative resolution
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27. www.google.com
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28.  In the example a client somewhere on the Internet needs the IP address of
www.google.com The following events take place:
 1.The client contacts NameServer1 with a recursive query for
www.google.com. The server must now return either the answer or an
error message.
 2.NameServer1 checks its cache and zones for the answer, but does
not find it, so it contacts a server authoritative for the Internet (that is, a
root server ) with an iterative query for www.google.com.
 3.The server at the root of the Internet does not know the answer, so
it responds with a referral to a server authoritative for the .com domain.
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29.  4.NameServer1 contacts a server authoritative for the .com domain with an
iterative query for www.google.com.
 5.The server authoritative for the .com domain does not know the exact
answer, so it responds with a referral to a server authoritative for the google.com
domain.
 6.NameServer1 contacts the server authoritative for the google.com
domain with an iterative query for www.google.com.
 7.The server authoritative for the google.com domain does know the
answer. It responds with the requested IP address.
 8.NameServer1 responds to the client query with the IP address for
www.google.com.
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30. DNS MESSAGES
The DNS query message consists of a header and question
records; the DNS response message consists of a header, question records,
answer records, authoritative records, and additional records.
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31. DNS messages
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32. Query and response messages
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33. Section Name Description
Contains fields that describe the
type of message and provide
important information about it.
Header
Also contains fields that indicate
the number of entries in the other
sections of the message.
Carries one or more “questions”,
that is, queries for information
Question
being sent to a DNS name
server.
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34. Section Name Description
Carries one or more resource
records that answer the
Answer
question(s) indicated in the
Question section above.
Contains one or more resource
records that point to
Authority authoritative name servers that
can be used to continue the
resolution process.
Conveys one or more resource
records that contain additional
information related to the
Additional
query that is not strictly
necessary to answer the queries
(questions) in the message.
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35.  The system which is in network request a web page to it‟s local server.
 The local DNS of that server maintain the details of the local clients
connected to it.
 From that server the page request forwarded to the DNS of the web content.
The request or the query for the particular page is in the name of that local
server.
 The query first processed by the resolver, it and then forward to the SLAVE
NAME SERVER. If the domain name is found in that it will return the IP
address to the requested resolver.
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36.  If the domain name is not found in the particular slave domain it and then
forward the detail of the requested resolver and the domain name to the
higher name server.
 The resolver details should be maintained in each level of name server if
that regarding to it‟s own zone.
 The several zones are there under one primary name server. The primary
name server of zones may be slave name server of another primary name
server.
 Each and every zone has it‟s unique salve name server.
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37.  The IP address of the requested page can be directly forwarded from the
current name server level., or the address should be returned through the
backward direction in the path the request came.
 The details of the requested result stored in slave name server. If the IP
address in found then the IP address and the domain name stored. Otherwise
the negative result be stored. This is caching.
 The first thing the slave name server has to do is search the particular
domain name in it‟s cached detail. If it is not found then it forward the
request to the higher level NS.
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39.  It is based on hierarchical database containing Resourses Records(RRs) that
includes IP address and other information about hosts.
 Key features:
 Variable-depth hierarchy for names
 Distributed Database
 Distribution controlled by the database.
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41.  Name Servers:
 These are server programs that hols information about a protion of the
domain name tree structure and the associated RRs.
 Resolver.
 These are programs that extract information from names servers in
response to client request is for an IP address corresponding to a given
domain name.
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42.  The need of DNS is demonstrated here.
 Without DNS we can not imagine the internet itself.
 The achievement done in the internet and web environment are the branch
from the DNS invention.
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