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…… DNS……

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AGENDA What is DNS ?

Why DNS ?

Working of DNS.

DNS Hierarchy

Features

Intro to IP

Resolving

Message format

ER diagram

DNS DB

Summary…

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What is DNS ?

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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Why DNS ? 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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Domain name 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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IP 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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Why IP(Internet Protocol)?

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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IP types?

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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IPv4

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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IPv6 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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Domain Name System

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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Domain Names 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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DNS HIERARCHY 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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ROOT SERVER

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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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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ICANN’S ROLE 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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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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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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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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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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Recursive resolution

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Iterative resolution

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Iterative and Recursive Queries

www.google.com

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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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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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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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DNS messages

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Query and response messages

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Section Name Description

Header

Contains fields that describe the type of message and provide important information about it. Also contains fields that indicate the number of entries in the other sections of the message.

Question

Carries one or more “questions”, that is, queries for information being sent to a DNS name server.

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Section Name Description

Answer

Carries one or more resource records that answer the question(s) indicated in the Question section above.

Authority

Contains one or more resource records that point to authoritative name servers that can be used to continue the resolution process.

Additional

Conveys one or more resource records that contain additional information related to the query that is not strictly necessary to answer the queries (questions) in the message.

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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.

Business Rules

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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.

Cntd….

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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.

Cntd….

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DNS Database 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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DNS Resource Record Format

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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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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.

Summary

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Thank you…!!!