Scenario
A company has just moved into a 3-floor office building. Each floor has 30 devices — 90 total — all connected to floor access switches (SW-F1, SW-F2, SW-F3). These uplink to a central distribution switch (SW-DIST), which connects to R1 and the internet. The initial design is a flat network: one subnet, no VLANs. Your job is to build it, verify it works, then discover exactly why it will fail as the company grows — and understand why VLANs are the answer.
Objectives
| # | Objective |
|---|
| 1 | Review the building topology and understand the flat network design |
| 2 | Configure R1 as the gateway — one interface, one subnet for all three floors |
| 3 | Configure a representative PC on each floor (PC-F1, PC-F2, PC-F3) |
| 4 | Verify inter-floor connectivity — confirm a flat LAN works across all three floors |
| 5 | Inspect the broadcast domain — show that all 90 devices share one enormous domain |
| 6 | Simulate a broadcast storm — observe the flat network's critical limitation, then preview the VLAN solution |
| 7 | Knowledge check — flat vs segmented networks, VLAN rationale, broadcast domain sizing |
Addressing Plan — 10.0.0.0/16 (flat — all floors)
| Device | IP Address | Subnet | Gateway |
|---|
| R1 Gi0/0 | 10.0.0.1 | 10.0.0.0/16 | — |
| PC-F1 (Floor 1) | 10.0.1.10 | 10.0.0.0/16 | 10.0.0.1 |
| PC-F2 (Floor 2) | 10.0.2.10 | 10.0.0.0/16 | 10.0.0.1 |
| PC-F3 (Floor 3) | 10.0.3.10 | 10.0.0.0/16 | 10.0.0.1 |
A /16 gives 65,534 usable hosts — enough for the whole building. Any valid host in 10.0.0.0/16 is accepted.
Supported Commands
| Device | Command | Purpose |
|---|
| All PCs | ip <addr> <mask> <gw> | Configure IP, mask and gateway |
| All PCs | show ip / show arp / ping | Standard host verification |
| R1 | show topology | Display the 3-floor building plan |
| R1 | show ip interface brief / show ip route | Verify R1 configuration |
| R1 | show broadcast-domain | Inspect the flat-network broadcast domain |
| R1 | show broadcast-storm | Simulate what happens when the flat LAN breaks — unlocks Broadcast Analyser |
| R1 | show vlan-preview | Preview the VLAN segmentation solution |
| R1 | configure terminal / interface / ip address / no shutdown | Standard IOS configuration |
| SW-DIST | enable / show mac address-table / show interfaces status | Distribution switch verification |
📊 After running show broadcast-storm, the Broadcast Analyser button appears — step through the heatmap, scalability calculator, and VLAN preview to understand exactly why this flat design fails.
This is the final lab of Block 1. It deliberately builds a design that works but has fundamental limitations — setting up Block 2 (Cisco Switching), where you'll fix it with VLANs.