Hi Rene,
Firstly, I am enjoying your lessons and tutorials. They are very informative and clearly laid out.
Nonetheless, I have been doing some thinking and trying to understand how an Ethernet Frame is encapsulated then decapsulated through the layers. So I have a question about the method an ethernet frame if transported from say Host A to Host B via a SOHO home router/modem.
Let’s say Host A sends an Ethernet Frame over the Internet to Host B. Host B is on a private LAN network with some other devices. The Ethernet Frame arrives at Host B’s SOHO home router/modem and for argument sake the frame has passed through the modem part and NAT has translated the destination IP address from public address to private address. This is where I am a little confused and have a question: What happens next?
I am assuming it goes to the router part of the SOHO device (layer 3). But the Ethernet Frame is layer 2 and only shows the destination MAC address. So, does the Ethernet Frame get decapsulated at this point to reveal the IP Packet for the router to understand the destination IP address for a split moment to then be encapsulated again when it goes to the switch part of the SOHO router/modem for it to be routed to Host B. Or does the Ethernet Frame decapsulated to layer 3 and the IP packet is sent to the switch where an ARP broadcast request is sent to locate Host B?
I have understood the lessons on ARP and the Ethernet Frame and IP Packet with the simple examples of a direct link. But not sure how it functions when an obstacle like a router is put in between. It seems there are more processes than needed to get a frame from A to B.
I maybe over complicating my thoughts or running ahead of myself here. But it is something I have been pondering about which I can’t get out of my head and need a clearer understanding.
Adrian G