Why this step exists
Before touching commands, a real engineer plans IPs first.
If you skip this, everything later feels confusing.
🧠 Rule for this step
- ❌ No CLI config
- ❌ No typing IPs into devices
- ✅ Just understand who gets what network
12.1 Decide the networks (simple & CCNA-clean)
We will use private IP space.
Head Office (City A)
| Purpose | Network |
|---|---|
| HQ Users (SW2) | 10.10.10.0 /24 |
| HQ Servers (SW3) | 10.10.20.0 /24 |
| HQ Wi-Fi | 10.10.30.0 /24 |
Branch Office (City B)
| Purpose | Network |
|---|---|
| Branch Users (SW4) | 10.20.10.0 /24 |
WAN Links
| Link | Network |
|---|---|
| R1 ↔ R2 (WAN) | 10.255.255.0 /30 |
Internet / ISP
| Link | Network |
|---|---|
| R1 ↔ ISP (R0) | 203.0.113.0 /30 (example public) |
CCNA does not care which public block — this is for learning.
12.2 Decide who is the gateway (VERY IMPORTANT)
Rule
The router interface facing the network is always the gateway
Head Office gateways (on HO-R1)
| Network | Gateway IP |
|---|---|
| 10.10.10.0 | 10.10.10.1 |
| 10.10.20.0 | 10.10.20.1 |
| 10.10.30.0 | 10.10.30.1 |
Branch gateway (on BR-R2)
| Network | Gateway IP |
|---|---|
| 10.20.10.0 | 10.20.10.1 |
WAN IPs
| Device | Interface IP |
|---|---|
| HO-R1 | 10.255.255.1 |
| BR-R2 | 10.255.255.2 |
ISP side
| Device | IP |
|---|---|
| ISP-R0 | 203.0.113.1 |
| HO-R1 (WAN) | 203.0.113.2 |
12.3 Where switches fit in
Switches do NOT route.
They:
- Don’t need IPs to forward traffic
- Only get management IPs later (optional)
So for now:
Ignore switch IPs
🧠 Lock-in sentence (remember this)
Routers own networks, switches forward frames, gateways live on routers.
❓ Check your understanding (answer mentally)
- Which device is the gateway for HQ users? → HO-R1
- Which device routes branch traffic? → BR-R2
- Which link is point-to-point? → R1–R2 WAN
If these make sense → you’re ready.
