A structured lesson workspace with readable content, hands-on examples, and a clean path to completion.
Stop memorizing layers. Learn jobs: switch connects devices in the same room/building. Router connects different networks together. AP connects wireless devices to the cable network. Firewall says no when policy says no. Name the problem, you name the box.
| Box | Job | Looks at | If it fails |
|---|---|---|---|
| Switch | Connect devices in same network | MAC address | One port dead, rest work |
| Router | Connect different networks / to ISP | IP address | Whole site loses internet |
| Access Point | Turn cable into WiFi | Radio + SSID | WiFi dead, wired PCs fine |
| Firewall | Block/allow by rule | IP + ports + state | App blocked, ping works |
Switch floods unknown addresses inside its network to learn. Router never floods — if it has no route and no default, it drops and sends ICMP Destination Unreachable. That's the exam trap: flooding = switch, dropping = router.
ip neigh shows the MAC your switch learned for the router. Your PC ARPs 'who has 10.10.20.1?' and remembers the answer. No manual config — switches and ARP learn by watching.
Office has 60 APs, each configured by hand. New SSID password means visiting 60 web pages. Wired PCs are fine, WiFi is inconsistent. What fixes it?
Select the safest next action.
You can now pick the right box for any ticket. Next: the OSI map — but as a troubleshooting tool, not memorization.
Finish the lesson once you have worked through the material. This awards ★ 35 XP.