🔐 Inter-VLAN Routing Lab (ROAS + Trunking)

📌 Overview

This lab demonstrates Inter-VLAN Routing using Router-on-a-Stick (ROAS) across two switches.

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🖥️ Topology

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🧩 VLAN Design

VLAN	Network
VLAN 10	10.0.0.0/26
VLAN 20	10.0.0.64/26
VLAN 30	10.0.0.128/26

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⚙️ Step 1 – Configure Access Ports

SW1

interface range f0/1-2
switchport mode access
switchport access vlan 10

interface range f0/3-4
switchport mode access
switchport access vlan 30

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SW2

interface range f0/2-3
switchport mode access
switchport access vlan 10

interface f0/1
switchport mode access
switchport access vlan 20

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🔗 Step 2 – Configure Trunks

SW1

interface g0/1
switchport mode trunk
switchport trunk allowed vlan 10,20,30
switchport trunk native vlan 1002

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SW2 (to SW1)

interface g0/1
switchport mode trunk
switchport trunk allowed vlan 10,20,30
switchport trunk native vlan 1002

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SW2 (to Router)

interface g0/2
switchport mode trunk
switchport trunk allowed vlan 10,20,30
switchport trunk native vlan 1002

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🌐 Step 3 – Router-on-a-Stick

interface g0/0
no shutdown

interface g0/0.10
encapsulation dot1q 10
ip address 10.0.0.62 255.255.255.192

interface g0/0.20
encapsulation dot1q 20
ip address 10.0.0.126 255.255.255.192

interface g0/0.30
encapsulation dot1q 30
ip address 10.0.0.190 255.255.255.192

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🧪 Step 4 – Connectivity Test

ping 10.0.0.1
ping 10.0.0.65
ping 10.0.0.129

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🚨 Troubleshooting Lesson

❌ Issue: VLANs could not communicate ✅ Cause: Trunk allowed VLAN mismatch

switchport trunk allowed vlan 10,20,30

💡 Always ensure trunks match on both sides

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🏁 Result

✔ Full inter-VLAN connectivity achieved ✔ ROAS working correctly ✔ Trunking verified

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🔥 Key Takeaways

• Trunks must match on BOTH sides
• ROAS enables routing with one interface
• VLAN design + trunking = foundation of networking

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💬 This lab helped reinforce trunk consistency and real-world troubleshooting skills.