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Seven Layers

Lesson 2 of 32 in Coddy's The OSI Model course.

The OSI model names seven layers. From the top (closest to you) to the bottom (closest to the wire):

  • 7. Application: the protocols programs speak (HTTP, DNS)
  • 6. Presentation: formats and encryption
  • 5. Session: opening and closing conversations
  • 4. Transport: ports, reliability (TCP, UDP)
  • 3. Network: IP addresses and routing
  • 2. Data Link: MAC addresses, one hop at a time
  • 1. Physical: actual bits on copper, fiber or radio

Learn the order cold. Every conversation about networking assumes it.

challenge icon

Challenge

Beginner

Print the seven layer names, top of the stack first (layer 7 down to layer 1), one per line, capitalized exactly as in the theory.

Expected output:

Application
Presentation
Session
Transport
Network
Data Link
Physical

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