What is Network Layer(Layer 3)?

Ø  It is responsible for end-to-end transportation of data across multiple networks.

Ø  Logical addressing and path determination( Routing) are described at this layer

Ø  The devices working at network layer are “Router”

Ø  The protocols work at Network layer are

Ø  Routed Protocols:

·     Routed protocols act as data carriers and defines logical addressing

·     IP, IPx, AppleTalk…. Etc

Ø  Routing Protocols:

·     Routing protocol performs path determination(Routing)

·     RIP, IGRP, EIGRP, OSPF…etc

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Ø  The network layer is responsible for the source-to-destination delivery of a packet, possibly

across multiple networks (links).

Ø  It is 3^rd layer of OSI reference model.

Ø  It is more useful to provide WAN connectivity.

Ø  Network layer works completely based on IP address i.e. Identification of particular destination devices at remote location is performed based on IP address.

Ø  Network layer takes the responsibility for routing packets from source to destination within or outside a subnet.

Ø  Network layer, DLL and physical layers come under the category of Hardware layer because there are  specific devices(Router,Layer-2 and Layer-3 switches) that are involved in these layers

Ø  Network layer functions are:

·     Packet Formation

·     Logical addressing

·     Internetworking

·     Routing

·     Error handling and diagnostics

a)    Packet Formation:

Ø  Datagram unit that is available at network layer is known as Packet

Ø  It contains

b)    Logical addressing:

Ø  IP address is logical address given to each and every device in the network

Ø  Recognition of devices in the network is done based on IP address

Ø  It is also called Layer-3 address or Network address

Ø  There are two versions:IPv4 and IPv6

c)    Internetworking:

d)    Routing:

Ø  Routing is the major function of network layer

Ø  Selecting the best shortest path to send packet to final destination with the help of some routing protocols e.g. RIP,IGRP,EIGRP,OSPF etc

e)   Error handling and diagnostics:

Ø  There are some protocols that works at network layer i.e. ICMP which deal with error reporting showing that all the devices are working properly and if error is coming that it will help to find out which type of error is existing