Objectives
| # | Objective |
|---|
| 1 | Configure a routed topology (PC1 — SW1 — R1 — SW2 — PC2) and achieve end-to-end connectivity |
| 2 | Map each CLI command and its output to the OSI layer it operates at |
| 3 | Observe Layer 1 (physical), Layer 2 (switch/MAC), and Layer 3 (IP/routing) symptoms in real output |
| 4 | Understand which OSI layers a ping traverses and why a switch only uses layers 1–2 |
| 5 | Use the OSI Layer Mapper to interactively explore all 7 layers with CLI evidence |
| 6 | Diagnose a fault by identifying which OSI layer it belongs to |
Key Concepts
| Layer | Name | What lives here |
|---|
| 7 | Application | HTTP, DNS, FTP — what the user touches |
| 6 | Presentation | Encoding, encryption, compression |
| 5 | Session | Establishing and managing sessions between apps |
| 4 | Transport | TCP/UDP — port numbers, reliability, segmentation |
| 3 | Network | IP addresses, routing — end-to-end delivery |
| 2 | Data Link | MAC addresses, Ethernet frames — hop-to-hop |
| 1 | Physical | Cables, signals, bits — the wire itself |
Commands in This Lab
| Command | Device | OSI Layer |
|---|
| show interfaces status | SW1 | Layer 1 + 2 — physical link state and port status |
| show mac address-table | SW1 | Layer 2 — MAC learning |
| show ip interface brief | R1 | Layer 3 — IP address and interface state |
| show ip route | R1 | Layer 3 — routing decisions |
| ping | PC1/PC2 | Layer 3 (ICMP) — tests end-to-end IP reachability |
| show arp | PC1/PC2 | Layer 2/3 boundary — resolves IP to MAC |
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The 🧱 OSI Layer Mapper unlocks after you run a successful ping. It maps every observable behaviour in this lab to the correct OSI layer with real CLI evidence.