Menu
Coddy logo textTech
START LEARNING
flag En iconEnglishdown icon

A Click Happens

Lesson 29 of 32 in Coddy's The OSI Model course.

Final chapter: follow one browser click through everything you have learned.

You type coddy.tech and press Enter. Before a single byte of the page can move, three things must happen in strict order:

  1. DNS: the name becomes an IP address, because packets travel to numbers, not names.
  2. TCP: the three-way handshake opens a connection to that IP on port 443.
  3. HTTP: only now does the actual request for the page go out.

Each step lives at a different layer, and each can fail independently, which is exactly how engineers narrow problems down.

challenge icon

Challenge

Beginner

Print the three protocols in the order they act when you click, one per line, uppercase.

Expected output:

DNS
TCP
HTTP

Try it yourself

Terminal

All lessons in The OSI Model

1Why Layers

The Layering IdeaSeven LayersNumbers and NamesRecap - The Stack

4The Network Layer

IP and TTLPing and ICMPRouting TablesRecap - Layer Three

7Encapsulation

Wrapping DataHeaders EverywhereReading a CaptureRecap - Follow the Wrap

2The Physical Layer

Bits on a WireHow Long Will It TakeDuplex and Collisions

5Transport: TCP and UDP

PortsThe TCP HandshakeTCP vs UDPSockets in ActionRecap - Layer Four

8The Journey of a Packet

A Click HappensCrossing the NetworksArriving and ClimbingRecap - End to End

3Data Link and MACs

Frames and MACsReading a MACARPRecap - Layer Two

6The Upper Layers

Session and PresentationThe Application LayerWatching the LayersRecap - Top of the Stack

Practice on your own: Terminal playground