unit 4 ipv4

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UNIT 4

NETWORK-LAYER IP

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CONTENT

INTRO TO INTERNET PROTOCOL (IP).

Datagram Format. - header de!r"#t"o$.

Fragme$tat"o$. - %a&"m'm Tra$er U$"t (%TU).

- F"ed Reated to Fragme$tat"o$.

O#t"o$.

- *"$ge-+,te O#t"o$. - %'t"#e-+,te O#t"o$.

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INTERNET PROTOCOL (IP)The network layer in version 4 consist of one main protocol

and three auxiliary ones.

1. The main protocol(IPv4) is responsi!le for packeti"in#

forwardin# and delivery of a packet at the network layer.

$. (I%&Pv4) helps IPv4 to handle some errors that may occur

in the network-layer delivery.

'. (I&P) is used to help IPv4 in multicastin#.

4. (*P) is used to #lue the network and data-link layers in

mappin# network-layer addresses to link-layer addresses.

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INTERNET PROTOCOL (IP4) IPv4 is an (unrelia!le + !est-effort) protocol of

data#ram delivery service.

,ecause Packets can !e corrupted !e lost arriveout of order or !e delayed and may create

con#estion for the network.

To make it relia!le IPv4 must !e paired with arelia!le transport-layer protocol such as T%P.

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INTERNET PROTOCOL (IP4) IPv4 is also a connectionless protocol that

uses the data#ram approach.

This means that each data#ram is handledindependently and each data#ram can follow

a different route to the destination.

This implies that data#rams sent !y the same

source to the same destination could arrive

out of order.

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DATARA% FOR%AT data#ram is a varia!le-len#th packet consistin# of two parts

header and payload (data).

The header is $ to / !ytes in len#th and contains information

essential to routin# and delivery.

Payload (data) is the main reason for creatin# a data#ram.

Payload is the packet comin# from other protocols that use the

service of IP.

%omparin# payload is the content of the packa#e the header is

only the information written on

the packa#e.

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DATARA% FOR%AT/ 0EADER

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DATARA% FOR%AT/ 0EADER 0ersion um!er(02*) defines the version of the IPv4

4-!its len#th and has the value of 4.

3eader en#th(32) defines the total len#th of theheader divide !y 4 4-!its len#th used to know when

the header stops and the data 5tart.

3eader len#th 6 4 7 value of (32)

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DATARA% FOR%AT/ 0EADER 5ervice Type defines how the data#ram should

!e handled 8-!its len#th.

Total en#th defines the total len#th ofdata#ram (header plus data) in !ytes 1/-!its

len#th.

This field helps the receivin# device to know when

the packet has completely arrived.

en#th of data 6 Total len#th - 3eader len#th

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DATARA% FOR%AT/ 0EADER Identification helps the destination in reassem!lin#

the data#ram 1/-!its len#th It knows that all

fra#ments havin# the same identification value should

!e assem!led into one data#ram.

9la#s '-!its len#th defines three fla#s

-leftmost !it is reserved (not used)

-The second !it (: !it) if its value 1 means that

packet not fra#ment ;therwise fra#ment.

-The third !it (& !it) if its value 1 means that this

data#ram is not the last fra#ment< there are more fra#ments

after this one.

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DATARA% FOR%AT/ 0EADER 9ra#mentation ;ffset shows the relative

position of this fra#ment with respect to the

whole data#ram1'-!its len#th

;ffset value 6 The first !yte num!er is divisi!le !y 8

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DATARA% FOR%AT/ 0EADER Time-to-live used to control the maximum num!er of

hops(routers) visited !y the data#ram 8-!its len#th<

=hen a source host sends the data#ram it stores a

num!er in this field.

This value is approximately two times the maximum

num!er of routers !etween any two hosts.

2ach router that processes the data#ram decrements

this num!er !y one.

If this value after !ein# decremented is "ero the

router discards the data#ram.

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DATARA% FOR%AT/ 0EADER Protocol 8-!it =hen the payload is encapsulated in

a data#ram at the source IP the correspondin#

protocol num!er is inserted in this field<

when the data#ram arrives at the destination the

value of this field helps to define to which protocol

the payload should !e delivered.

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DATARA% FOR%AT/ 0EADER 3eader checksum 1/-!its field header checksum

field to check the header ,ecause 2rrors in the IP

header can !e a disaster.

If the destination IP address is corrupted the packet

can !e delivered to the wron# host.

If the protocol field is corrupted the payload may !e

delivered to the wron# protocol.

If the fields related to the fra#mentation are

corrupted the data#ram cannot !e reassem!led

correctly at the destination and so on.

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DATARA% FOR%AT/ 0EADER 5ource ddresses '$-!its define the address of

the source.

:estination ddresses '$-!its define the

address of the destination.

ote that the value of these fields must remain

unchan#ed durin# the time data#ram travels

from the source host to the destination host.

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DATARA% FOR%AT/ 0EADER E1A%PLE

3eader len#th 6 4 7 value of (32)

3eader len#th 6 4 7 > 6 $.

en#th of data 6 Total len#th - 3eader len#th

en#th of data 6 4 - $ 6$

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EXAMPLE OF CHECKSUM

CALCULATION IN IPV4

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ONE %AY A*K W0Y WE NEEDT0I* 0EADER ?

=hen a machine (router or host) receives a

frame it drops the header and the trailer

leavin# the data#ram.

in many cases we really do not need thevalue in this field.

3owever there are occasions in which the

data#ram is not the only thin# encapsulated

in a frame< it may !e that paddin# has !een added.

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FRA%ENTATION 2ach router decapsulates the IP data#ram from the frame it

receives processes it and then encapsulates it in another

frame.

The format and si"e of the received frame depend on the

protocol used !y the physical network throu#h which theframe has ?ust traveled.

The format and si"e of the sent frame depend on the protocol

used !y the physical network throu#h which the frame is #oin#

to travel.

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FRA%ENTATION/ (%TU) 2ach link-layer protocol has its own frame format. ;ne of the

features of each format is the maximum si"e of the payload

that can !e encapsulated.

The total si"e of the data#ram must !e less than this

maximum si"e. maximum len#th of the IP data#ram e@ual to />>'> !ytes.

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FRA%ENTATION data#ram can !e fra#mented !y the source host or any router

in the path.

=hen a data#ram is fra#mented each fra#ment has its own

header with most of the fields repeated !ut some have !een

chan#ed. The reassem!ly of the data#ram however is done only !y the

destination host !ecause each fra#ment !ecomes an

independent data#ram.

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OPTION* data#ram header can have up to 4 !ytes of options.

;ptions can !e used for network testin# and

de!u##in#.

lthou#h options are not a re@uired part of the IP

header option processin# is re@uired of the IPsoftware.

This means that all implementations must !e a!le to

handle options if they are present in the header.

some options can !e chan#ed !y routers which forces

each router to recalculate the header checksum.

There are one-!yte and multi-!yte options.

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OPTION* The header of the IPv4 data#ram is made of two

parts

The fixed part is $ !ytes lon#

The varia!le part comprises the options that can

!e a maximum of 4 !ytes to preserve the

!oundary of the header.

;ptions are divided into two !road cate#ories

sin#le-!yte options and multiple-!yte options.

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OPTION*/ SINGLE-BYTE OPTIONS

There are two sin#le-!yte options

o ;peration is a 1-!yte option used as a

filler !etween options.

2nd of ;ption is a 1-!yte option used for

paddin# at the end of the option field.

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OPTION* / %ULTLIPLE-+YTE *ecord *oute is used to record the Internet

routers that handle the data#ram. It can list up

to nine router addresses. It can !e used for

de!u##in# and mana#ement purposes.

5trict 5ource *oute is used !y the source to

predetermine a route for the data#ram The

sender can choose a route with a specific type of

service such as minimum delay or maximumthrou#hput.

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OPTION* / %ULTLIPLE-+YTE oose 5ource *oute is similar to the strict source

route !ut it is less ri#id. 2ach router in the list

must !e visited !ut the data#ram can visit other

routers as well.

T"metam#/ is used to record the time of data#ram

processin# !y a router =e can estimate the time it

takes for a data#ram to #o from one router to

another.

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IP ADDRE**IN

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CONTENT

IP4 ADDRE**E*

-Addre *#a!e.

-0"erar!h, "$ addre"$g

-Ca' Addre"$g.

-Cae Addre"$g.

-D,$am"! 0ot Co$"g'rat"o$ Proto!o(D0CP).

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IP4 ADDRE**E* The Internet address (IP address) the identifier used to

identify the connection of each device to the Internet.

The IP address may !e chan#ed if the device is moved

to another network.

The IPv4 address is a '$-!it address that uni@uely and

universally defines the connection of a host to the

Internet.

IPv4 addresses uni@uely 2ach address defines only one

connection to the Internet. IPv4 addresses universally the addressin# system must

!e accepted !y any host that wants to !e connected to

the Internet.

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ADDRE** *PACE n address space is the total num!er of addresses used

!y the protocol.

If a protocol uses ! !its to define an address the

address space is $A!.

In !inary notation an IPv4 address is displayed as '$

!its.

In hexadecimal notation an IPv4 address is displayed

as 8 hexadecimal di#its.

2ach octet is often referred to as a !yte.

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0IERARC0Y IN ADDRE**IN '$-!it IPv4 address is hierarchical divided

into two parts.

The first part of the address called the

prefix defines the network. the second part of the address called the

suffix defines the node.

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CLA**FUL ADDRE**IN IPv4 address was desi#ned with a fixed len#th

prefix.

To accommodate !oth small and lar#e networks

three fixed-len#th prefixes were desi#nedinstead of one (n = 8, n = 16, and n = 24).

The whole address space was divided into five

classes (class , % : and 2).

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CLA**FUL ADDRE**IN class network len#th is 8 !its first !it defines the

class seven !its as the network identifier. there are only

1$8 networks in the world that can have a class address.

class , network len#th is 1/ !its first two !its 1 definethe class14 !its as the network identifier. there are only

1/'84 networks in the world that can have a class ,

address.

In class % network len#th is $4 !its three !its 11 definethe class $1 !its as the network identifier. there are

$BC1>$ networks in the world that can have a class %

address.

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CLA**FUL ADDRE**IN

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ADDRE** DEPLETION %lass can !e assi#ned to only 1$8 or#ani"ations in the world

!ut each or#ani"ation needs to have a sin#le network with

1/CCC$1/ nodes.

5ince there may !e only a few or#ani"ations that are this

lar#e most of the addresses in this class were wasted(unused).

%lass , addresses were desi#ned for midsi"e or#ani"ations !ut

many of the addresses in this class also remained unused.

%lass % addresses have a completely different flaw in desi#n

The num!er of addresses that can !e used in each network($>/ nodes) was so small that most companies were not

comforta!le usin# a !lock in this address

%lass 2 addresses were almost never used wastin# the whole

class.

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IP ADDRE**E*The values and -1 (all 1s) have special meanin#s. The value

means this network or this host. The value of -1 is used as a

!roadcast address to mean all hosts on the indicated network.

'/

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IP ADDRE**E*

All the hosts in a network must have the same network number. This property of IP addressing can cause problems as networks grow. For

example……

The problem is the rule that a single class A ! or " address refers to

one network not to a collection of #A$s.

The solution is to allow a network to be split into several parts for

internal use but still act like a single network to the outside world.

'C

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IP ADDRE**E*

To implement subnetting the main router needs a subnet mask thatindicates the split between network % subnet number and host.

For example if the university has a ! address&'().*).).)+ and (*departments it could use a ,-bit subnet number and a ')-bit hostnumber allowing for up to , /thernets each with a maximum of

')00 hosts.

The su!net mask can !e written as $>>.$>>.$>$.. nalternative notation is +$$ to indicate that the su!net maskis $$ !its lon#.

'8

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*U+NETTIN AND*UPERNETTIN

In 5u!nettin# a class or class , !lock is

divided into several su!nets.

2ach su!net has a lar#er prefix len#th than the

ori#inal network.

5upernettin# was devised to com!ine several

class % !locks into a lar#er !lock to !e

attractive to or#ani"ations that need more thanthe $>/ addresses availa!le in a class % !lock.

This idea did not work either !ecause it makes

the routin# of packets more difficult.

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ADANTAE OF CLA**FUL ADDRE**IN

It had one advanta#e

iven an address we can easily find the

class of the address and since the prefix

len#th for each class is fixed we can find theprefix len#th immediately.

In other words the prefix len#th in classful

addressin# is inherent in the address< noextra information is needed to extract the

prefix and the suffix.

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CLA**LE** ADDRE**IN In classless addressin# varia!le-len#th !locks are

used that !elon# to no classes.

=e can have a !lock of 1 address $ addresses 4

addresses 1$8 addresses and so on. the whole address space is divided into varia!le

len#th !locks.

The prefix defines the !lock (network)<

The suffix defines the node(device).

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PREFI1 LENT0/ *LA*0NOTATION

the prefix len#th n is added to the address

separated !y a slash.

The notation is informally referred to as slash

notation and formally as classless interdomainroutin# (%I:*).

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ADDRE** INFOR%ATION 1.The num!er of addresses in the !lock is

found as 6 $A('$Dn)<n is prefix.

$.To find the first address we keep the nleftmost !its and set the ('$ D n) ri#htmost

!its all to s.

'.To find the last address we keep the nleftmost !its and set the ('$ D n) ri#htmost

!its all to 1s.

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ADDRE** %A*K

The address mask is a '$-!it num!er in which

The prefix !its are set to 1s.

The rest of the !its are set to s.

1.The num!er of addresses in the !lock

6 ;T (mask) E 1.

$.The first address in the !lock 6(ny address in the!lock) : (mask).

'.The last address in the !lock 6(ny address in the

!lock) ;* F(;T (mask)G.

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NETWORK ADDRE** 2 +LOCK ALLOCATION

etwork address is particularly important

!ecause it is used in routin# a packet to its

destination network.

,lock llocation I% does not normally

allocate addresses to individual Internet users. It

assi#ns a lar#e !lock of addresses to an I5P.

The num!er of re@uested addresses needs to

!e a power of $.

The re@uested !lock needs to !e allocated where

there is an ade@uate num!er of conti#uous

addresses availa!le in the address space.

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*U+NETTIN

num!er of addresses is

the prefix len#th is n

the assi#ned num!er of addresses to each

su!network is su! the prefix len#th for each su!network is nsu!

The num!er of addresses in each su!network

should !e a power of $.

The prefix len#th for each su!network should !efound usin# the followin# formula

The startin# address in each su!network should !e

divisi!le !y the num!er of addresses in that

su!network

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ADDRE** AREATION

=hen !locks of addresses are com!ined to create

a lar#er !lock routin# can !e done !ased on the

prefix of the lar#er !lock.

I% assi#ns a lar#e !lock of addresses to an

I5P. 2ach I5P in turn divides its assi#ned !lock

into smaller su!!locks and #rants the su!!locks

to its customers.

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*PECIAL ADDRE**E* ...+'$ is called the host address.

$>>.$>>.$>>.$>>+'$ is called the limited-

!roadcast address.

1$C...+8 is called the loop!ack address.

private addresses 1...+8 1C$.1/..+1$1B$.1/8..+1/and 1/B.$>4..+1/.

$$4...+4 is reserved for multicast addresses.

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NETWORK ADDRE** TRAN*LATION (NAT)

The technolo#y allows a site to use a set of private addresses

for internal communication and a set of #lo!al Internet

addresses (at least one) for communication with the rest of

the world.

The site must have only one connection to the #lo!al Internet

throu#h a T-capa!le router that runs T software.

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NAT ADDRE** TRAN*LATION

unit 4 ipv4

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