- This is also known as IP layer or inter network layer.
- This layer is responsible for host to host(source-to-destination) delivery of the packet and also routing the packet through router or switches that is helps in routing mechanism.
- Also responsible for reassembling the fragmented packet and then passing to Transport layer
- It adds logical address called IP address for source and destination to the segment coming from upper layer, which aids in host to host delivery of packet.
- In this layer data are referred as packet.
Below Diagram depicts how the packets are processed at Network Layer for source, destination and router.
Network Layer at switch or router:
The network layer at the switch or router is responsible for routing the packet. When a packet arrives, the router or switch consults its routing table and finds the interface from which the packet must be sent. The packet, after some changes in the header, with the routing information is passed to the data link layer again.
Some of the fields which never changes at the router are: IP address, Protocol, version where as TTL, checksum and checksum( in case of fragmentation) and flag related to fragments can be changed.
Network Layer at destination:
The network layer at the destination is responsible for address verification; it makes sure that the destination address on the packet is the same as the address of the host. If the packet is a fragment, the network layer waits until all fragments have arrived, and then reassembles them and delivers the reassembled packet to the transport layer.
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