Download Network Layer

Network Layer
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The Network layer, or OSI Layer 3, provides
services to exchange the individual pieces of
data over the network between identified end
devices.
To accomplish this end-to-end transport, Layer 3
uses four basic processes:
 Addressing
 Encapsulation
 Routing
 Decapsulation
Routing
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The source and destination hosts are not always
connected to the same network. In fact, the
packet might have to travel through many
different networks. Along the way, each packet
must be guided through the network to reach its
final destination.
Intermediary devices that connect the networks
are called routers. The role of the router is to
select paths for and direct packets toward their
destination. This process is known as routing.
Each route that a packet takes to reach the next
device is called a hop.
Protocols in Network Layer

The Internet Protocol (IPv4 and IPv6) is
the most widely-used Layer 3 data
carrying protocol
Why separate hosts into network ?

Performance
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Packet tracer broadcast domain
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Security
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Address Management
Network layer in an internetwork
Network layer at the source
Network layer at a router
Network layer at the destination
IP Addressing (IPv4)
Internet Address
Class full Addressing
Note:
An IP address is a 32-bit address.
The Internet Protocol was designed as a protocol with low overhead. It
provides only the functions that are necessary to deliver a packet from a
source to a destination over an interconnected system of networks. The
protocol was not designed to track and manage the flow of packets. These
functions are performed by other protocols in other layers.
IPv4 basic characteristics:
•Connectionless - No connection is established before sending data packets.
•Best Effort (unreliable) - No overhead is used to guarantee packet delivery
Here, Unreliable means simply that IP does not have the capability to
manage, and recover from, undelivered or corrupt packets.
•Media Independent - Operates independently of the medium carrying the
data.
Note:
The IP addresses are unique
and universal.
Dotted-decimal notation
Example 1
Change the following IP addresses from binary notation to dotteddecimal notation.
a.
10000001 00001011 00001011 11101111
b.
11111001 10011011 11111011 00001111
Example 2
Change the following IP addresses from dotted-decimal notation to
binary notation.
a.
111.56.45.78
b.
75.45.34.78
Note:
In classful addressing, the address
space is divided into five classes: A, B,
C, D, and E.
Finding the class in binary notation
Finding the address class
Example 3
Find the class of each address:
a.
00000001 00001011 00001011 11101111
b.
11110011 10011011 11111011 00001111
Finding the class in decimal notation
Example 4
Find the class of each address:
a.
227.12.14.87
b.
252.5.15.111
c.
134.11.78.56
Netid and hostid
Blocks in class A
Note:
Millions of class A addresses are
wasted.
Blocks in class B
Note:
Many class B addresses are wasted.
Note:
The number of addresses in class C is
smaller than the needs of most
organizations.
Blocks in class C
Network address
Note:
In class full addressing, the network
address is the one that is assigned to
the organization.
Example 5
Given the address 23.56.7.91, find the network address.
Ans. 23.0.0.0 (kelas A)
Example 6
Given the address 132.6.17.85, find the network address.
Ans. 132.6.0.0 (kelas B)
Example 7
Given the network address 17.0.0.0, find the class.
Note:
A network address is different from a
netid. A network address has both
netid and hostid,
with 0s for the hostid.
Sample internet (classful)
Gateway
IP Private
Private addresses (others are called Public IP or Global address) :
Range
Total
10.0.0.0
to
10.255.255.255
224
172.16.0.0
to
172.31.255.255
220
192.168.0.0
to
192.168.255.255
216