IPv4Overview

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IPv4 Overview


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IP Protocol

This is host to host network layer connection less datagram

protocol with no guarantee of reliability. It is a unreliable protocol

bz it does not provide any error and flow control. It can only

detect the error and discard the corrupted packet.

IP Datagram

Packet in IP layer are called datagram.it is a variable length packet

with two parts Header and Data .The header is 20-60 bytes in

length and contains information required for routing and delivery.

data field is of variable length.


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Structure of IP frame header


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Version (VER). This 4-bit field defines the version of the IP protocol. Currently

the version is 4. However, version 6 may totally replace version 4 in the

future. This field tells the IPv4 software running in the processing machine that the

datagram has the format of version 4. All fields must be interpreted as specified

in the fourth version of the protocol. If the machine is using some other version of

IPv4, the datagram is discarded rather than interpreted incorrectly.

Header length (HLEN). This 4-bit field defines the total length of the datagram

header in 4-byte words. This field is needed because the length of the header

is variable (between 20 and 60 bytes). When there are no options, the header length

is 20 bytes, and the value of this field is 5 (5 x 4 = 20). When the option field is

at its maximum size, the value of this field is 15 (15 x 4 = 60).

Services. This is 8-bit field. This field, previously called service type, is now called

differentiated services.it defines the class of datagram for quality of service purpose.

Total length field defines the total length of the datagram including the header.

Length of data =total length - header length

Since the field length is 16 bits, the total length of the IPv4 datagram is limited to

65,535 (216 - 1) bytes, of which 20 to 60 bytes are the header and the rest is data.


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Identification:--This 16-bit field identifies a datagram originating from the source

host. When a datagram is fragmented, the value in the identification field is copied

to all fragments . The identification number helps the destination in reassembling

the datagram. It knows that all fragments having the same identification value

must be assembled into one datagram.

Flags:- This is a 3-bit field. The first bit is reserved and it should be zero. The

second bit is called the do not fragment bit. If its value is 1, the machine must not

fragment the datagram . If its value is 0, the datagram can be fragmented if

required. The third bit is called the more fragment bit. If its value is 1, it means the

datagram is not the last fragment; there are more fragments after this one. If its

value is 0, it means this is the last or only fragment.

More fragmentation bitDo not fragment bit Reserved bit

Fields Related to Fragmentation


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Fragmentation offset

This 13-bit field shows the relative position of this fragment with respect to the

whole datagram. It is the offset of the data in the original datagram measured in

units of 8 bytes.


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The bytes in the original datagram are numbered 0 to 3999. The first fragment

carries bytes 0 to 1399. The offset for this datagram is 0/8 =O. The second

fragment carries bytes 1400 to 2799; the offset value for this fragment is 1400/8

= 175. Finally, the third fragment carries bytes 2800 to 3999. The offset value

for this fragment is 2800/8 =350. Remember that the value of the offset ismeasured in units of 8 bytes. This forces hosts that fragment datagrams to

choose a fragment size so that the first byte number is divisible by 8.

Time to live. A datagram has a limited lifetime in its travel through an internet.

This field was designed to hold a timestamp, which was decremented by each

visited router. The datagram was discarded when the value became zero. all themachines must have synchronized clocks and must know how long it takes for

a datagram to go from one machine to another. this field is used mostly to

control the maximum number of routers visited by the datagram. When a

source host sends the datagram, it stores a number in this field. This value is 2

times the maximum number of routes between any two hosts. Each router thatprocesses the datagram decrements this number by 1.If this value is zero, the

router discards the datagram .


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This field is needed because routing tables in the Internet can

become corrupted . A datagram may travel between two or more

routers for a long time without ever getting delivered to thedestination host. This field limits the lifetime of a datagram .

this field is also used to intentionally limit the journey of the

packet. if the source wants to confine the packet to the local

network, it can store 1 in this field. When the packet arrives at the

first router, this value is decremented to 0, and the datagram is

discarded


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A no-operation option is a I-byte option used as a filler between options.

An end-of-option option is a I-byte option used for padding at the end of the option

field. It, however, can only be used as the last option.

A record route option is used to record the Internet routers that handle the datagram. Itcan list up to nine router addresses. It can be used for debugging and management

purposes.A strict source route option is used by the source to predetermine a route for the datagram

as it travels through the Internet. The sender can choose a route with a specific type of

service, such as minimum delay or maximum throughput. Alternatively, it may choose a

route that is safer or more reliable for the sender's purposeA loose source route option is similar to the strict source route, but it is less rigid. Each

router in the list must be visited, but the datagram can visit other routers as well.

A timestamp option is used to record the time of datagram processing by a router.

Knowing the time a datagram is processed can help users and managers track the

behavior of the routers in the Internet. We can estimate the time it takes for a datagram

to go from one router to another.


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Checksum

First the value of the checksum field is set to O. Then the entire header is

divided into 16-bit sections and added together. The result (sum) is

complemented and inserted into the

checksum field . The checksum in the IP packet covers only the header, not the

data. There are two good reasons for this.

First, all higher-level protocols that encapsulate data in the IP datagram have

a checksum field that covers the whole packet. Therefore, the checksum forthe IP datagram does not have to check the encapsulated data.

Second, the header of the IP packet changes with each visited router, but the

data do not. So the checksum includes only the part that has changed. If the

data were included, each router must recalculate the checksum for the whole

packet, which means an increase in processing time.


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Services provided by IP

Addressing32 bit address used by intermediate router to select a path

through the network for the packet. FragmentationIP packet may be split in to smaller packets. This permit a

large packet to travel through a n/w that can handle the smaller packets.

Packet time outtime to live

Address Space. IP uses 32-bit addresses . An address space is the total number of addresses

used by the protocol. IP uses 32-bit addresses, which means that the address

space is 232 or 4,294,967,296 (more than 4 billion).


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Protocol

This 8-bit field defines the higher-level protocol that uses the services of

the IP layer. An IP datagram can encapsulate data from several higher-levelprotocols such as TCP, UDP, ICMP, and IGMP. This field specifies the final

destination protocol to which the IP datagram is delivered. since the IP protocol

carries data from different other protocols, the value of this field helps the receiving

network layer know to which protocol the data belong


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Source address. This 32-bit field defines the IP address of the source. This fieldmust remain unchanged during the time the IP datagram travels from the source

host to the destination host.

Destination address. This 32-bit field defines the IP address of the destination .This field must remain unchanged during the time the IP datagram travels from the

source host to the destination host.

OptionsOptions, as the name implies, are not required for every datagram. They can be

used for network testing and debugging.


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IP Address


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IP Addresses:

Classful Addressing


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An IP address is a

32-bitaddress.


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The IP addressesare

unique.


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RULE:

addr15addr1

addr2

addr41addr31

addr226

....

....

..

....

If a protocol usesNbits to

define an address,the address space is 2N

because each bit can have two

different values (0 and 1)andNbits can have 2Nvalues.


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The address space of IPv4 is

232

or4,294,967,296.

An address space is the total number of addresses used by the

protocol.


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01110101 10010101 00011101 11101010

Binary Notation


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Dotted-decimal notation


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Every router and host on internet has a unique IP address .all IP address are of

32 bit and they use source and destination field of the IP header. The first part

of address is called network ID which identify the network on the internet and

second called the host ID used to identify the individual host on that network.

Classes of IP address :-


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Netid and hostid


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In classful addressing,

the address space is

divided into five classes:A,B, C,D, andE.


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Class Ranges of Internet Addresses


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Class A address

The n/w field is of 7 bit and the host field is of 24 bits . One bit is used for the class

type. So the n/w field can have numbers b/w 0 to 127. but the host number ranges from

0.0.0.0 to 127.255.255.255. hence in class A there can be 127 types of n/ws. bit 0 in fist

field indicates that it is class A n/w address.

27 26 25 24 23 22 21 20

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 1

.0 1 1 1 1 1 1 1

Samewaytotal number of host will be ranges from 0. 0.0.0 to 127. 255.255.255

0 7 bit / network ID 24 bit host ID

0

127

32 bit


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Millions of class A addressesare wasted.


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Class B address

The first field defines the class type and second field defines the

networks. And last field defines the hosts. The n/w field values lies

b/w 128 to 191.the first block covers the address from

128.0.0.0 to 128.255.255.255 and last block covers from 191.0.0.0 to

191.255.255.255.

10 14 bit / network id 16 bit / host id

10 (6 bit) 000000 8 bit( 00000000) Host id (8 + 8 )

Range from 0 to 255

Ranges from 128 to 191

32 bit

Range from 0 to 255

Range from 0 to 255

14 bits (6 + 8)


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Many class B addressesare wasted.


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Class C address32 bit

110 Network ID ( 21 bit) Host ID (8 bit)

110 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Host ID(8 bit)

21 bits(5+8+8)

110 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 HostID(8 bit)

272625 24 23 22 21 20 27 26 25 24 23 22 21 20 27 26 25 24 23 22 21 20

00192

110 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 HostID(8 bit)

223

255255

0

255

192.0.0.0

223.255.255.255


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Class C address32 bit

110 Network ID ( 21 bit) Host ID (8 bit)

110 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Host ID(8 bit)

21 bits(5+8+8)

110 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 HostID(8 bit)

272625 24 23 22 21 20 27 26 25 24 23 22 21 20 27 26 25 24 23 22 21 20

00192

110 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 HostID(8 bit)

223

255255

0

255

192.0.0.0

223.255.255.255


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Class D address

1110 Multicast ID

32 bit

1 1 1 0 4 bit 8 bit 8 bit 8 bit

1 1 1 0 0 0 0 0 00000000 0000000 0000000

27 26 25 24 23 22 21 20

00

0224

224.0.0.0

1 1 1 0 1 1 1 1 11111111 11111111 1111111127 26 25 24 23 22 21 20

239

255255 255

239.255.255.255


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Class D addresses

are used for multicasting;

there is only

one block in this class.

Cl E dd


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Class E address

1111 Reserved for future use

32 bit

1 1 1 1 4 bit 8 bit 8 bit 8 bit

1 1 1 1 0 0 0 0 00000000 0000000 0000000

27 26 25 24 23 22 21 20

00

0240

240.0.0.0

1 1 1 1 1 1 1 1 11111111 11111111 1111111127 26 25 24 23 22 21 20

255

255255 255

255.255.255.255


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Class E addresses are reserved

for special purposes;most of the block is wasted.

Fi di th dd l


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Finding the address class


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Finding the class in decimal notation

Date post:	06-Apr-2018
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IPv4Overview

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