Why this exists

This exists as revision material

Full Picture Projects— screenshots of results for the matching exercise.

Initial command

Create A diagram: browser → TCP → IP → Ethernet → switch

Network stack: browser → switch

How a request travels down the stack. Each layer wraps the data from the layer above and adds its own header before passing it on — that wrapping is encapsulation.

flowchart TD
    A["Browser (application)<br/><small>Creates the HTTP request data</small>"]
    B["TCP (transport)<br/><small>Adds ports, sequencing, reliability</small>"]
    C["IP (network)<br/><small>Adds source + destination IP address</small>"]
    D["Ethernet (link)<br/><small>Adds MAC addresses, frames the bits</small>"]
    E["Switch<br/><small>Reads MAC, forwards to the right port</small>"]
    A --> B --> C --> D --> E

What each layer adds

Layer	Adds	Purpose
Browser (application)	The HTTP request itself	The actual data you want to send
TCP (transport)	Source + destination ports, sequence numbers	Reliable, ordered delivery to the right program
IP (network)	Source + destination IP address	Routing across networks — the door out
Ethernet (link)	Source + destination MAC address, framing	Delivery on the local wire
Switch	— (reads, doesn’t add)	Forwards the frame out the correct port

Encapsulation

Each step down wraps the previous one:

Your HTTP data gets a TCP header →
that whole thing gets an IP header →
that gets an Ethernet header.

By the time it hits the wire it’s a frame with three nested envelopes.

What the switch does

The switch only cares about the outermost envelope — the Ethernet/MAC header. It reads the destination MAC and forwards the frame out the correct port, without ever opening the IP or TCP layers inside. Those get unwrapped later, layer by layer, at the receiving machine.

Rule of thumb: switches work at the MAC layer (Layer 2), routers at the IP layer (Layer 3).