11 - IPaddresses & Subnetting

8/14/2019 11 - IPaddresses & Subnetting

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IP addressing

For communication between twosystems, each should be able toaddress another.

All components of the networkshould have unique addresses.

Layer 3 follows a particular type ofaddressing scheme .

It is a logical addressing scheme.


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IP addressing


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IP addressingThese addresses are not actual

network addresses.

They represent and show theconcept of address grouping.

This uses the A or B to identify the

network and the number sequenceto identify the individual host .


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IP addressing A computer may be connected to more

than one network. In this situation, the system must be

given more than one address. Each address will identify the

connection of the computer to adifferent network.

A device is not said to have an address,but that each of the connection points,or interfaces, on that device has anaddress to a network .


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IP addressing


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IP addressing Each computer in a TCP/IP network must

be given a unique identifier, or IP

address.This address, operating at Layer 3, allows

one computer to locate another computeron a network .

IP address is different from MAC or Layer2 address.


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IP addressing An IP address is a 32-bit sequence of 1s and

0s.

To make the IP address easier to use, theaddress is usually written as four decimalnumbers separated by periods.

This way of writing the address is called thedotted decimal format.

In this notation, each IP address is writtenas four parts separated by periods, or dots.


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IP addressing IP address in bit representation and

dotted decimal notation are

11000000101010000000000100001000 192.168.1.8

Each part of the address is called anoctet because it is made up of eightbinary digits


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IP addressing The dotted decimal notation is an easier

method to understand than the binary

ones and zeros method. This dotted decimal notation also

prevents a large number oftransposition errors that would result if

only the binary numbers were used . Using dotted decimal allows number

patterns to be more easily understood .


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IP addressing IP addressing is a hierarchical

addressing scheme.

Every IP address has two parts One part identifies the network where

the system is connected.

and a second part identifies thatparticular system on the network.


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IP addressing IP addresses are divided into classes

to define the large, medium, and

small networks Class A addresses are assigned to

larger networks

Class B addresses are used formedium-sized networks

Class C for small networks


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The stability of the Internet dependsdirectly on the uniqueness of

publicly used network addresses. Duplicate network IP addresses

prevent the router from performingits job of best path selection.

Unique addresses are required foreach device on a network.


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IP addressing

A procedure was needed to make sure thataddresses were in fact unique.

Originally, an organization known as theInternet Network Information Center(InterNIC) handled this procedure.

InterNIC no longer exists and has beensucceeded by the Internet Assigned

Numbers Authority (IANA).


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IP addressing

IANA carefully manages the remainingsupply of IP addresses to ensure that

duplication of publicly used addressesdoes not occur.

Duplication would cause instability in theInternet and compromise its ability to

deliver datagrams to networks.


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IP addressing

Public IP addresses are unique. No two machines that connect to a

public network can have the same IPaddress because public IP addresses areglobal and standardized.

All machines connected to the Internetagree to conform to the system.

Public IP addresses must be obtainedfrom an Internet service provider (ISP)or a registry at some expense.


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IP addressing

With the rapid growth of theInternet, public IP addresses were

beginning to run out. New addressing schemes, such as

classless interdomain routing

(CIDR) and IPv6 were developed tohelp solve the problem.


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IP addressing

Private IP addresses are another solution tothe problem of the impending exhaustion ofpublic IP addresses.

As mentioned, public networks require hoststo have unique IP addresses.

However, private networks that are not

connected to the Internet may use any hostaddresses, as long as each host within theprivate network is unique.


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IP addressing

Many private networks exist alongsidepublic networks.

However, a private network using justany address is strongly discouragedbecause that network might eventuallybe connected to the Internet.

RFC 1918 sets aside three blocks of IPaddresses for private, internal use.


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IP addressing

These three blocks consist of one Class A, arange of Class B addresses, and a range ofClass C addresses.

Addresses that fall within these ranges arenot routed on the Internet backbone. Internet routers immediately discard private

addresses. If addressing a nonpublic intranet, a test

lab, or a home network, these privateaddresses can be used instead of globallyunique addresses.


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Connecting a network using privateaddresses to the Internet requires

translation of the private addressesto public addresses.This translation process is referred

to as Network Address Translation

(NAT). A router usually is the device that

performs NAT.


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IP addressing

Subnetting is another method of managingIP addresses.

This method of dividing full network addressclasses into smaller pieces has preventedcomplete IP address exhaustion.

It is not always necessary to subnet a small

network. However, for large or extremelylarge networks, subnetting is required.


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Subnetting a network means touse the subnet mask to divide the

network and break a large networkup into smaller, more efficient andmanageable segments, or subnets.


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The system administrator must resolvethese issues when adding and expandingthe network.

It is important to know how many subnets ornetworks are needed and how many hostswill be needed on each network.

With subnetting, the network is not limited

to the default Class A, B, or C networkmasks and there is more flexibility in thenetwork design.


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IP addressing

Subnet addresses include the network portion,plus a subnet field and a host field.

The subnet field and the host field are created

from the original host portion for the entirenetwork.

The ability to decide how to divide the originalhost portion into the new subnet and host fields

provides addressing flexibility for the networkadministrator.


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IP addressing

To create a subnet address, anetwork administrator borrows bitsfrom the host field and designatesthem as the subnet field.

The minimum number of bits thatcan be borrowed is two.

When creating a subnet, where onlyone bit was borrowed the networknumber would be the .0 network.


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IP addressing

The broadcast number would then bethe .255 network.

The maximum number of bits that canbe borrowed can be any number thatleaves at least two bits remaining, forthe host number.


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What is Subnetting? Borrowing 2 or more bits from the

HOST portion of the IP address toextend the NETWORK portion.

Divides your allotted IP addressesinto separate, discrete networks.

Final host part of the IP addressmust contain at least 2 bits.


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Benefits of Subnetting

Limits the extent of Broadcast Domains Instead of going to all IP addresses on the

network, broadcasts are forwarded only to

those machines on the same subnet.

Better organization of IP addresseswithin the enterprise.

Different media might be used fordifferent LAN segments.


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Subnet Mask

Indicates what portion of the IPaddress represents the network

10001100.10110011.11110000.1100100011111111.11111111.00000000.00000000

10001100.10110011.00000000.00000000

140 . 179 . 240 . 200

Class B address

Class B Net Mask

Network Part

140 . 179


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Default Subnet Masks

Class A Subnet Mask 255 . 0 . 0 . 0

Class B Subnet Mask 255 . 255 . 0 . 0

Class C Subnet Mask 255 . 255 . 255 . 0

B i H Bi


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Borrowing Host Bitsto Subdivide theNetwork Space

At least 2 bits must be borrowedfrom the host part of the IPaddress

At least 2 bits must be left for theHost part of the IP address


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Mask

11111111.11111111.11100000.00000000

255 . 255 . 224 . 0

Network Part Host Part

11111111.11111111.00000000.00000000

255 . 255 . 0 . 0

Network Part Host Part

Three bits borrowed from

Host Part to extend the

Network Part of the address


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Example Class B Subnet

000

001010

011

100

101

110

111

Network Address Cant be Used

001 Useable Subnet Address010 Useable Subnet Address

011 Useable Subnet Address



Broadcast Address Cant be Used

000

001010

011

100

101

110

111

Network Address Cant be Used





Broadcast Address Cant be Used

PossibleNetworks


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Host Addresses on the 011Subnet

01100000.00000000

01100000.00000001

01100000.00000010.

.

.01111111.11111101

01111111.11111110

01111111.11111111

Network Address

Useable Address

Useable Address.

.

.Useable Address

Useable Address

Broadcast Address

(32 x 256)-2 = 8190 Total Useable

Hosts on the 011 Subnet

Subnet Host

11 - IPaddresses & Subnetting

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