eth0 & ecapsulation explanation

What is eth0 ?

In Linux systems, eth0 is the first network device (ethernet card) plugged into a slot.

Additional ethernet cards plugged will become eth1, eth2 , eth3 ….. etc


What is encapsulation ?

The transmission of one network protocol within another.

As data moves down the protocol stack from the application layer to the data link layer, each protocol encapsulates the higher level by adding its own header to the block of data passed to it.

Encapsulation is process that moving Data from layer 3 to layer 2 by adding header to the layer 2 .

The data with IP protocol ( layer 3 ) can be moved to Data Link Protocol (layer 2) , the data is tunneling through difference protocol . This process is called “encapsulation” .

Encapsulation involve adding new header to its lower layer .

Encapsulation also involve "tunneling" through difference protocol.

Example : adding Mac Addr as a new header to the packer , and later become Frame .

Frame = Mac Address ( new header ) + Packet + tail ------ happen on layer 2

Packet = IP Address ( header ) + TCP header + Data + tail ------ happen on layer 3

Packet = TCP header + data ------ happen on layer 4
Above process , that involve adding header is called encapsulation.