The Network layer is used mainly for the routing purpose in the network. The concept of subnet comes into picture for this layer.

Same with protocols, two different subnet may be operating on different protocols which are not compatible with each other.

Network layer has the responsibility to route the packets from source to destination, mapping different addressing schemes and protocols.

The logical-physical addresses mapping. It provides a logical address to each device on a network such as on the internet where each machine has its own unique IP (Internet Protocol) address.

Fragmentation (divides packets into several fragments when a router’s maximum transmission unit’s (MTU) size is less than a packet size).

Subnet traffic control and usage accounting (to keep track of the packet information that is sent to next node or returned as a result of the router’s buffer).

Function of Network Layer

• Addressing devices and networks.

• Populating routing tables or static routes.

• Queuing incoming and outgoing data and then forwarding them according to quality of service constraints set for those packets.

• Internetworking between two different subnets.

• Delivering packets to destination with best efforts.

• Provides connection oriented and connection less mechanism.

Features of Network Layer

• Quality of service management

• Load balancing and link management

• Security

• Interrelation of different protocols and subnets with different schema.

• Different logical network design over the physical network design.

• L3 VPN and tunnels can be used to provide end to end dedicated connectivity.