How to create a simple network topology

Building a VLAN Network Topology with Cisco Packet Tracer

🗒️ Introduction

In this tutorial, I’ll show you how to create a network topology with 17 PCs, 3 switches, and 1 router using Cisco Packet Tracer.

We’ll divide the network into four VLANs (VLAN10, VLAN20, VLAN30, VLAN40) and color-code each VLAN to make it visually clear.

Each VLAN has its own IP range, as shown below:

VLAN	IP Range	Subnet Mask	Usable Hosts
VLAN10	10.0.0.1 – 10.0.0.30	255.255.255.224 (/27)	30
VLAN20	10.0.0.33 – 10.0.0.62	255.255.255.224 (/27)	30
VLAN30	10.0.0.65 – 10.0.0.94	255.255.255.224 (/27)	30
VLAN40	10.0.0.97 – 10.0.0.126	255.255.255.224 (/27)	30

We’ll configure each PC with:

1. IP Address
2. Subnet Mask
3. Default Gateway

After configuring the PCs, we’ll move on to the switches and router-on-a-stick setup.

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Step 1: Create the Network Topology

Drag and drop:

• 1 Router
• 3 Switches (SW1, SW2, SW3)
• 17 PCs

Then connect:

• PCs → Switches
• SW1 ↔ SW2 ↔ SW3
• SW1 ↔ Router (R1)

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Step 2: PC Configuration

For each PC:

• Go to Desktop → IP Configuration
• Set:
  • IP Address (based on VLAN range)
  • Subnet Mask: 255.255.255.224
  • Default Gateway (e.g. 10.0.0.30 for VLAN10)

Repeat for all 17 PCs.

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Step 3: Configure the Switches

We’ll start with SW1, then repeat similar steps for SW2 and SW3.

1. Change Hostname:

   Switch> enable
   Switch# configure terminal
   Switch(config)# hostname SW1

2. Create VLANs:

   SW1(config)# vlan 10
   SW1(config-vlan)# name v10
   SW1(config)# vlan 20
   SW1(config-vlan)# name v20
   SW1(config)# vlan 30
   SW1(config-vlan)# name v30
   SW1(config)# vlan 40
   SW1(config-vlan)# name v40

3. Assign Ports to VLANs: Example for VLAN10 and VLAN40:

   SW1(config)# interface range fastEthernet0/1-3
   SW1(config-if-range)# switchport mode access
   SW1(config-if-range)# switchport access vlan 10
   
   SW1(config)# interface range fastEthernet0/4-5
   SW1(config-if-range)# switchport mode access
   SW1(config-if-range)# switchport access vlan 40

4. Configure Trunk Ports (for SW1-SW2 connection):

   SW1(config)# interface g0/1
   SW1(config-if)# switchport mode trunk
   SW1(config-if)# switchport trunk allowed vlan 10,20,30,40
   SW1(config-if)# switchport trunk native vlan 1001

Repeat similar configurations for SW2 and SW3, adjusting port assignments based on connected PCs.

Step 4: Configure Router-on-a-Stick

To enable inter-VLAN routing, configure sub-interfaces on the router.

1. Enable the Main Interface:

   Router(config)# interface g0/0
   Router(config-if)# no shutdown

2. Configure Sub-Interfaces:

   Router> enable
   Router# configure terminal
   Router(config)# interface g0/0.10
   Router(config-subif)# encapsulation dot1Q 10
   Router(config-subif)# ip address 10.0.0.30 255.255.255.224
   
   Router(config)# interface g0/0.20
   Router(config-subif)# encapsulation dot1Q 20
   Router(config-subif)# ip address 10.0.0.62 255.255.255.224
   
   Router(config)# interface g0/0.30
   Router(config-subif)# encapsulation dot1Q 30
   Router(config-subif)# ip address 10.0.0.94 255.255.255.224
   
   Router(config)# interface g0/0.40
   Router(config-subif)# encapsulation dot1Q 40
   Router(config-subif)# ip address 10.0.0.125 255.255.255.224

Step 5: Test Connectivity & Troubleshooting

Intra-VLAN Testing

• Test: Ping from PC1 (VLAN10, 10.0.0.1) to PC4 (VLAN10, 10.0.0.4) on SW1.
  • Issue: If the ping fails, check VLAN assignments on SW1 ports.
• Simulation: Test PC1 to all PCs connected to SW1 to confirm packet forwarding.

Inter-Switch Connectivity

• Test: Ping from PC16 (VLAN10, SW3) to PC4 (VLAN10, SW2).
  • Result: Successful ping confirms inter-switch trunking.
• Test: Ping from PC16 (VLAN10, SW3) to PC100 (VLAN40, SW3).
  • Result: Successful ping confirms inter-VLAN routing via the router.

Troubleshooting SW1

• Issue: VLAN assignments on SW1 ports were lost, causing ping failures.
• Solution:
  1. Reconfigure VLAN assignments on SW1 ports.
  2. Save the configuration:

     SW1# write memory

Final Ping Tests

• Test: PC16 (VLAN10) to PC1 (VLAN10, via SW1).
  • Result: Successful.
• Test: PC16 (VLAN10) to PC65 (VLAN30, via SW1).
  • Result: Successful, confirming inter-VLAN routing.

Key Takeaways

• Verify VLAN Assignments: Ensure switch ports are correctly assigned to VLANs.
• Save Configurations: Always use write memory to persist configurations.
• Test Connectivity: Validate both intra-VLAN and inter-VLAN communication to ensure a robust network.

Your network is now fully functional! ✅