Network Layer

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

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

Packet tracer broadcast domain

Security

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)IP Addressing (IPv4)

Internet Address

Class full Addressing

An IP address is a 32-bit address.

NoteNote::

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 deliveryHere, 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.

The IP addresses are unique and universal.

NoteNote::

Dotted-decimal notation

Example 1Example 1

Change the following IP addresses from binary notation to dotted-decimal notation.

a. 10000001 00001011 00001011 11101111

b. 11111001 10011011 11111011 00001111

Example 2Example 2

Change the following IP addresses from dotted-decimal notation to binary notation.

a. 111.56.45.78

b. 75.45.34.78

In classful addressing, the address space is divided into five classes: A, B,

C, D, and E.

NoteNote::

Finding the class in binary notation

Finding the address class

Example 3Example 3

Find the class of each address:

a. 000000001 00001011 00001011 11101111

b. 111111110011 10011011 11111011 00001111

Finding the class in decimal notation

Example 4Example 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

Millions of class A addresses are wasted.

NoteNote::

Blocks in class B

Many class B addresses are wasted.

NoteNote::

The number of addresses in class C is smaller than the needs of most

organizations.

NoteNote::

Blocks in class C

Network address

In class full addressing, the network address is the one that is assigned to

the organization.

NoteNote::

Example 5Example 5

Given the address 23.56.7.91, find the network address.

Ans. 23.0.0.0 (kelas A)

Example 6Example 6

Given the address 132.6.17.85, find the network address.

Ans. 132.6.0.0 (kelas B)

Example 7Example 7

Given the network address 17.0.0.0, find the class.

A network address is different from a netid. A network address has both

netid and hostid, with 0s for the hostid.

NoteNote::

Sample internet (classful)

Gateway

IP Private

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

Private addresses (others are called Public IP or Global address) :