NETWORK LAYER DESIGN ISSUE:

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24 Οκτ 2013 (πριν από 3 χρόνια και 9 μήνες)

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MUDULI

ACADEMY

NETWORK LAYER DESIGN ISSUE:

Network layer is the third layer of OSI
reference model. It

responds to services requests from the
transport layer and issues services requests to the data link layer.

There are
two network layer design issues
. These

are

1.

Service provided to the transport layer

2.

Internal design of subnet

Service provided to the transport layer:

1.

The services should be independent of the subnet technology

2.

The network address which is made available to transport layer must use a uniform
numberi
ng plan.

Internal organization of network layer
:

Basically there are two methods of organizing the subnet as

1.

To use connection service

2.

To use connection less service

In connection oriented service, a connection is called as virtual circuit

In connection le
ss service, the independent packet are called as datagram

LOGICAL ADDRESSING:

The address provided by the network layer is called as logical address. The network layer uses
IPV4 and IPV6 address to identify a particular node.

IPV4 address is represented
by binary and dotted decimal.


IPV6 address is represented by hexadecimal colon.

IPV4 ADDESS
:

An IPV4 address is a 32
-
bit address that uniquely and universally defines the connection of a
device to the internet.

The address is to be unique and universal

As the address is
unique and universal.
Unique

in the
sense

each address defines one and only
one connection to the internet.


Universal

in the sense that the addressing system must be accepted by any host that wants to be
connected to the internet.



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ACADEMY

NOTATION
:

IPV4 address has two types of notation

1.

Binary notation

2.

Dotted decimal notation.

Binary notation:

In this notation, the IPV4 address is displayed as 32 bits. It contains four bytes.

Example:




10010101


01110101


00011101


11101010

Dotted deci
mal notation:

In dotted decimal notation the address are written by using dot(.) with decimal values.

Example:



100000000

00001011


00000011


00011111




128


.


11


. 3


. 31

Classful

addressing
:

In classful
addressing the address space is divided into five classes A, B, C, D and E.

Each class occupies some part of the address space






MUDULI

ACADEMY


NETID AND HOST ID
:

In class full addressing an IP address is in class A, B and C are divided into netid and hosted



Class

A
=
one byte
(

netid
)

and three bytes
(

hosted)
.


Class

B
=

two bytes
(
netid
)

and two bytes
(

hosted)
.


Class

C
=

three bytes
(
netid
)

and one byte
(

hosted)
.

Class D designed for multicast address

Class E is designed for use as reserved address for future purpose.

Example
:

Find the class of each address

1.

00000001 00001011 00001011 11101111

Sol: The first bit is zero so it belongs to class A address

2.

11000001 10000011 00011011 11111111

Sol: Here first 2 bits are 1 and third bit is zero so it belongs to class C add
ress.

3.

252.5.15.111

Sol: The first byte is 252 which lies between 240 and 255 so it belongs to class E address




MUDULI

ACADEMY

CLASS A address:

The network field is 7 bit long and the host field is of 24 bit length. The 0 in the first field
identifies that it is a clas
s
A network address
. Here the first bloc
k covers from o.o.o.o to
255.255.255.2555 and last block covers from 127.0.0.0 to 127.255.255.255.

0

Network

host





7bits 24bits



CLASS B address:

In this
address the host number 0.0 and 255.255 are reserved. The first block covers from
128.0.0.0 to 128.0.255.255 and last block covers from 191.255.0.0 to 191.255.255.255.

10

Network

host



CLASS C address:

In this address the first block covers from 192.0.0.
0 to 192.0.0.255 and last block covers from
223.255.255.0 to 223.255.255.255.

110

Network

host


CLASS D address:

This address allows the multicast in which a datagram is directed to multiple host.

1110

Multicast address


CLASSS E address:

This address is

usually user for future reference.

11110

Reserved for future use









MUDULI

ACADEMY

Question:

For the address 24.46.8
.95 , identify the type of network and find the network address.

Sol:

The first byte is 24. i.e it is between 0 and 127. Hence it is a class
A network

so only the first
byte

defines the netid, we find the
network address by replacing the hosted with 0’s

24

46.8.95







Replaced with hosted by 0s







There the network address is
24. 0. 0.
0


MASK:

Mask is a 32
-
bit number made of contiguous

1’s followed by contiguous 0’s. These masks are
used to find out netid and hostid.

Example:

Consider a class c address 192.15.28.16

Here 192.1.15.28 corresponds to the network port address and 16
correspond

to the host port.

Therefore

the mask is 255.255.
255.0 for this address.

Address


192.15.28.16

Mask


255.255.255.0

It uses a notation called as slash notation/CIDR notation.

Example:

Class



binary




dotted
-
decimal



using slash

A 1111111 0000000 0000000
0 0000000 2
55.0.0.0



/8




24

0.0.0



MUDULI

ACADEMY


SUBNETTING
:

The process dividing a network into several smaller groups and assign each group a smaller
networks called subnet. This process of dividing a large block in smaller groups is called
subnetting

SUPERNETTING:

It is a combination of several class C
address
to form a large range of address called
supernetting.

CLASS LESS addressing
:

Class less address means there is no concept of classes.

IPV6:

An IPV6 address consists of 16 bytes. These 16 bytes divided into 8 s
ections each one is 2 bytes
long .It uses a special notation called as hexadecimal colon notation.

So IPV6 uses hexadecimal format, it contains many zero digit. To abbreviate this address drop
the leading zero not trailing zero.


EXAMPLE:


FDEC: 0074:0000
:0000:0000:B0FF:0000:FFF0



FDEC: 74:0:0:0:B0FF:0:FFF0




FDEC

:

74::B0FF

:

0

:

FFF0

After
dropping

the zero, if the address
contains continuous

zeros then remove the continuous
zero and replace with double semicolon.

Categories of IPV6 address:

Unicast:


A unicast address defines a single computer. A packet sent to a unicast address is delivered to
that specific computer.

Multicast:

Multicast address is used to define a group of hosts.




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ACADEMY

Anycast
:

In anycast address when a packet is send then the p
acket is delivered to nearest one.


INTERNET PROTOCOL (IP):

It is the host
-
to
-
host network layer delivery protocol for the internet. it is an unreliable and
connection less datagram protocol.

Datagram:

Packets in the IP layer are called datagram. A datagra
m is a variable length packet consisting of
two parts i.e header and data.





VER:

It gives the version of IP

HLEN:

It defines the length of the header

DS:


This field is use for quality and services

TOTAL LENGTH:

It gives the total length of the
datagram including header

FLAGS:

3 bit field(first bit reserved+ do not fragment + more fragment bit)




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ACADEMY

FRAGMENT OFFSET:

It gives the relative position of the fragment with respect to whole datagram


PROTOCOL:

It gives which protocol is used for the
services of IP layer.

HEADER CHECKSUM:

This field is used for computation of the checksum.

SOURCE ADDRESS:

It defines the IP address of the source

DESTINATION ADDRESS:

It defines the IP address of the destination

OPTION:

This field is used for testing an
d debugging

IPV6

The fields of IPV6 is as follows




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ACADEMY

VER:

Gives version of the IP.

PRI:

It defines the priority of the packet during the transmission at the time of congestion.

FLOW LEVEL:

This filed is designed for the flow of data.

PAYLOAD LENGTH
:

It
defines the total length of the a IP datagram.

NEXT HEADER:

It defines the header follows the base header in the datagram.

HOPLIMIT:


This fields defines Time to live field of IP

SOURCE ADDRESS:


It identifies the original source of datagram


DESTINATION
ADDRESS:

It defines the final destination of the datagram.

Subnet:

T
he process of dividing a network into several groups and assign each group
smaller networks

called subnet. The process of dividing a large block in smaller groups is called subnetting.








MUDULI

ACADEMY

Subnet mask:

The number of 1’s in the subnet mask is
more than

the number of 1’s in the corresponding
default mask. In subnet mask we change some of the left most 0’s in the default mask to make
a subnet mask.






255.255.0.0

Default mask



Sunet mask











3 extra 1’s

Superneting:

It is a combination of several class c address to form a large range of address called
supernetting.

11111111 1111111
1

00000000 00000000

11111111 11111111

11100000 00000000