network layer-05-ip

8/14/2019 Network Layer-05-IP

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Computer NetworksCPS 422

NETWORK LAYERAddressing in the Internet

Faisal Amjad CPS 422

Behrouz A. Forouzan


Internet Address

For communication on the Internet, we need touniquely identify everydevice connected to theInternet.

The identifier used in the network layer of theInternet model to identify each device on theInternet is called the Internet Address, InternetProtocol Address or commonly, the IP Address

An IP address is a 32-bit binary address thatuniquely and universally defines the connection ofa host or a router to the Internet

A host can have multiple IP addresses, but twohosts cannot have the same IP address on theInternet


Internet Address - Notations

There are two notations to represent IPaddresseso Binary notation ando Dotted Decimal notation

Binary Notationo Written as 32 bits usually with a space after every

Octet (8 bits) e.g. 10101010 01110101 10110100 11011101o Can also be called as consisting of 4-bytes

Dotted-Decimal Notationo To make the IP addresses compact and easier to read,

they are written in decimal form with a decimal point(dot) separating the bytes

o Because of 8-bits in a byte, every number in the dotteddecimal notation is between 0 and 255


Internet Address - Notations

Example of the two Notations

10000000 00001011 00000011 00011111

128.11.3.31


IP Address - Classes

Initially IP addressing used the concept of classesof address

This architecture is called Classful Addressing

Due to some problems (to be discussed later) a

new architecture called Classless Addressing wasintroduced

Systems are slowly migrating to Classlessaddressing


IP Classful Addressing

In classful addressing, the address space isdivided into five classes: A,B,C,D and E

The first few bits of an IP address tell the Classof address

Class A

Class B

Class C

Class D

Class E

First Byte Second Byte Third Byte Fourth Byte

0

10

110

1110

1111


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IP Address Finding the Class

1st Bit 2nd Bit 3rd Bit 4th Bit

Class A Class B Class C Class D

Class E

Start

0

1

0

1

0

1

0

1


Class A

Class B

Class C

Class D

Class E

First Byte Second Byte Third Byte Fourth Byte0 to 127

128 to 191

192 to 223

224 to 239

240 to 255

IP Address Finding the Class inDecimal Notation


IP Address NetID & HostID In classful addressing, an IP address is divided into two

partso NetID ando HostID

These parts are of varying lengths, depending upon theclass

Class A

Class B

Class C

Class D

Class E

First Byte Second Byte Third Byte Fourth Byte

0

10

110

1110

1111

Net ID

Net -------------- ID

Net ------------------------- ---------- ID

Host ------------------- ID

Host ------------------------- ------------ ID

Host --- ID

Multicast -------------Address

Reserved for Future Use


IP Address Classes & Blocks

The division of IP addresses into classes revealsthat every class can have a fixed number of blocksof addresses, with a fixed size

For example, class A is divided into 128 blocks (0to 127), with each block having different netIDo All numbers in one byte, from 0 to 127 have the first bit

equal to 0 (Hence these numbers show they belong to aclass A Address)

o Hence, the first block covers addresses from 0.0.0.0 to0.255.255.255 with netID = 0

o The second block covers addresses from 1.0.0.0 to1.255.255.255 with netID = 1

o The last block of class A covers addresses from127.0.0.0 to 127.255.255.255 with netID = 127



Note that for each block of addresses (in a classA address), the first byte (netID) is the same

The other 3-bytes (hostID) (in a class Aaddress)can take any value within the given range

When an organization is given a block ofaddresses, the first address in it is used toidentify the organization on the Internet, hence itis called the Network Address, NOTany individualhost



For Future Use1E

For multicasting1D

2562,097,152C

65,53616,384B

16,777,216128A

HostsBlocksClass Too Many

Too Many

Too Less

Result is a lot of address wastage


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IP Network Address

Network address is an address that defines thenetwork itself

It cannot be assigned to a hostProperties of network address are

o All hostID bytes are 0s

o It defines the network to rest of the Internet, helps inefficient routing of packets

o It is the first address in the block

o Given the network address, we can find the class ofaddress


Subnetting

A portion of IP address indicates the network(netID) and a potortion indicates the hosts on thenetwork (through hostID)

It means that there is a sense of heirarchy in IPaddressing

To reach a host on the Internet, we must firstreach the network by using netID

Then we must reach the host itself by using thehostID

Therefore we can conclude that IP has two levelsof heirarchy


Subnetting

An organization often needs to assemble its hostsinto groups i.e. the network needs to be subdividedinto subnetworks (or subnets)

As the networks have network address to identifyit on the Internet, each subnet has a subnetaddress to identify the subnet within the network(and not outside it)

Subnetting, therefore introduces another level ofhierarchy. Although the subnets in total stillappear as a single network to rest of the Internet


Subnetting Example

Suppose our college is allotted a single class BBlock of IP address 141.14.0.0

Also suppose that there are only four departmentsin our college namely CS, EE, IS and BasicSciences (or BS)

Logically we would like to create separate subnetsfor each of the departments

All departments would also be required to beinter-connected e.g. with routers


Subnetting Example

CS EE

IS BS

To rest of the Internet

141.14.192.2

141.14.192.1

Subnet:141.14.192.0

Network Address:141.14.0.0

Subnet:141.14.128.0

Subnet:141.14.50.0 Subnet:

141.14.115.0

141.14.192.254

141.14.192.3 141.14.128.1 141.14.128.254

141.14.128.2

141.14.128.3

141.

14.5

0.

2

141.

14.1

15.

2

141.14.50.1 141.14.50.254 141.14.115.1 141.14.115.254

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