Stage 1 · Lesson 1 of 8
The OSI and TCP/IP models
Networking is split into layers so each problem can be solved on its own. The has seven: physical (signals on a cable), data link (frames between neighbours, using ), network ( between networks, using ), transport (TCP or UDP between programs), and three upper layers for the application.
The TCP/IP model folds these into four or five. As data goes down the layers, each adds its own header, which is called encapsulation; the receiver strips them in reverse. Engineers use the layer numbers as shorthand every day: "a Layer 2 issue" means and VLANs, "Layer 3" means routing.
Common trapmemorising the layer names without knowing which device, address and header belongs to each one, which is what troubleshooting actually needs.
A question to check yourself, an AI practice session and 1 cheat sheet entry come with the full roadmap. Unlock
Resources for this stage
Start with· follow one of these
- PlatformFreeCisco Networking Academy
Cisco · Beginner
Start with the free, self-paced Networking Basics course; it uses Packet Tracer from the first modules
- VideoFreeComputer Networking: A Top-Down Approach (Video Lectures)
Jim Kurose and Keith Ross · Intermediate
Free university-level lectures from the authors of the classic textbook, for the why behind every layer
Practise
Keep handy
Also worth your time
A clear comparison of the two transport protocols and when each one fits
- Beej's Guide to Network ProgrammingGo deeper
If you code, write a tiny TCP and UDP client and server to see the transport layer from the inside