I have read that encapsulation takes place down the layers while decapsulation takes place up the layers. In essence, the encapsulation starts at Application layer all the way upto Physical layer. Assume we have a sender A and receiver B.Sender A wants to http to a server B. So for the encapsulation down the layers on A side we would have,
Application(http)-Presentation-Session-Transport(TCP port 80)-Network(IP address of A)-Data link(Mac)-Physical(Bits 0 and 1).
From above, we can say that PDU(Protocol data unit) of upper layer(say Network Layer) becomes the data of the lower layer(say Data link layer).
Essentially,(Data+control Info )of Network layer =( Data ) of data link layer
Now coming to the receiver side B(decapsulation process) Step 1: The Physical layer header is stripped off
Step 2: The data link layer header is stripped off
Step 3: The network layer header is stripped off and so on
Q1: is the above understanding correct?
Q2: I am getting confused as to why data link layer info is stripped off first? I mean, when we do ARP, we first look at IP address(layer 3) and request for mac address(layer 2 info).
I understand that there is a value called Ethertype, that tells what upper layer protocol is being used(e.g mpls or IPv4 or IPv6) ?