Virtual LANs (VLANs) and Trunking

Lesson Objectives

By the end of this lesson, you will:

1. Understand the purpose and functionality of Virtual LANs (VLANs).
2. Learn how VLANs improve network segmentation and security.
3. Explore trunking and its role in connecting multiple VLANs.
4. Gain practical experience with VLAN and trunking configurations.

Introduction: Optimizing Network Segmentation

Imagine a large office building with multiple departments (e.g., HR, Finance, IT). While everyone is connected to the same physical network, isolating traffic for each department improves security and performance. This is where VLANs come into play.

Virtual LANs (VLANs) allow logical segmentation of a physical network into smaller, isolated networks, and trunking enables communication between these VLANs across network devices.

Configuring VLANs and Trunking

VLAN Configuration (on a Cisco switch):

1. Create VLANs:

    configure terminal vlan 10 name HR vlan 20 name Finance vlan 30 name IT 

2. Assign VLANs to Ports:

    interface FastEthernet0/1 switchport mode access switchport access vlan 10 interface FastEthernet0/2 switchport mode access switchport access vlan 20 

Trunking Configuration:

1. Set a Trunk Port:

    interface GigabitEthernet0/1 switchport mode trunk switchport trunk allowed vlan 10,20,30 

Hands-On Exercises

Exercise 1: Plan a VLAN Setup

Scenario:

• An office has 50 employees across three departments: Sales, IT, and Support.

Task:

1. Assign VLAN IDs:
   • Sales: VLAN 100
   • IT: VLAN 200
   • Support: VLAN 300
2. Map switch ports to each VLAN.

Exercise 2: Simulate VLANs and Trunking

1. Use a network simulator (e.g., Cisco Packet Tracer).
2. Create three VLANs and connect two switches using a trunk link.
3. Verify VLAN traffic isolation by pinging devices within the same VLAN.

Exercise 3: Troubleshoot VLAN Connectivity

Scenario: Devices in VLAN 20 cannot communicate across switches.

Steps:

1. Verify VLAN configuration on both switches:

    show vlan brief 

2. Check trunking status:

    show interfaces trunk 

3. Ensure VLAN 20 is allowed on the trunk port.

Key Takeaways

1. VLANs: Enable logical segmentation of networks to improve security and performance.
2. Trunking: Facilitates communication between VLANs across network devices.
3. 802.1Q Standard: Ensures VLAN tagging and identification on Ethernet frames.

What’s Next?

In the next chapter, we’ll explore Network Address Translation (NAT) and its role in enabling devices with private IPs to communicate on the Internet.

Your understanding of VLANs and trunking is growing—let’s keep building! 🚀