1

I just saw level 1-2-3-4 (from Physical to Transport)
We have the following : 7 Layers of OSI - Communication

The thing is: We know that at layer 3 there is the IP protocol that uses DNS Server to get the IP Address of the destination (for example a website).
Then we know that with the IP, our system call ARP to know what the MAC Address of the destination is (because Internet is based on Ethernet and Ethernet works with MAC right?).

Then we know the route to follow to communicate with the other client.

So imagine we went to send a mail : we go in gmail, we enter our data in the mail and then we hit enter, does the following happen ? :

  • With DNS and ARP we get the MAC Address of the destination and the route to follow (not sure about this)
  • We know that at layer 4 there is the three-way handshake where systems communicates and determine how they will send and receive our data.
  • But how can they communicate ?
  • Does our router know the route of the DNS initially ?
  • How can we communicate if the route is not etablished between our 2 points ?
  • How can they communicate at layer 4 without passing through Network, Data and Physical ?

I bet they MUST communicate by this way but how can you communicate and send data if you don't have establish the communication initially ?

My main problem is to know HOW system communicates at layers above 1 and how they do if they pass through other layers ?

Maybe this post is a little confusing but I'm a bit lost, thanks !
If you have any video or gif or anything that show everything that happend when we send a message or anything to another pc through all layers it would be fantastic

5
  • It's exactly what I was looking for ! Thanks a lot – Rom Jun 20 '17 at 21:14
  • The first answer explains everything really well but it doesn't explain how the PC/Server will de-encapsulate from layer 1 to layer 7.. any clue ? – Rom Jun 20 '17 at 21:29
  • It's just the reverse of the encapsulation. What part are you confused about? – Ron Trunk Jun 20 '17 at 22:03
  • This may help. – Eddie Jun 20 '17 at 23:11