VLAN Configuration and Port Assignment

Hello! Welcome to our next lesson.

In the previous session, you performed the essential initial setup for a Cisco switch, including configuring a management IP address on interface vlan 1. This gave you a first glimpse into the concept of VLANs. Today, we'll dive deep into what VLANs are, why they are a cornerstone of modern networking, and how you can create your own to segment a network.

This lesson directly addresses the goal of configuring VLANs and assigning switch ports to them. By the end, you'll be able to take a single physical switch and logically divide it into multiple, separate virtual networks, a fundamental skill for improving network performance and security.

1. Understanding the Need for VLANs

Before we jump into configuration, it's crucial to understand the problem that VLANs solve. By default, all ports on a switch are part of the same network, or more specifically, the same broadcast domain. This means a broadcast frame (like an ARP request for an unknown device) sent from one host is forwarded to every other host on the switch. In a large network, this can create significant unnecessary traffic, hurting performance and posing security risks.

VLANs (Virtual Local Area Networks) are the solution. They allow you to logically segment a switch into multiple broadcast domains. Devices in one VLAN cannot directly communicate with devices in another VLAN at Layer 2, as if they were connected to entirely separate physical switches.

Let's watch a video that explains this concept clearly.

2. Configuring VLANs and Access Ports

Now that you understand the "why," let's move on to the "how." The process involves two main steps:

1. Creating the VLAN on the switch.
2. Assigning switch ports to that VLAN.

Ports assigned to a single VLAN are called access ports. These are typically the ports that connect to end devices like PCs, printers, and servers.

Let's look at the following topology. Our goal will be to configure the switch to match this design.

The following reading provides a concise, step-by-step guide to the commands you'll need.

Step-by-Step Configuration

Let's apply these commands to achieve the setup from the diagram above.

Step 1: Create and Name the VLANs

First, we enter global configuration mode and create each VLAN. It's best practice to name them for easy identification.

Switch> enable
Switch# configure terminal
Switch(config)# vlan 10
Switch(config-vlan)# name Marketing
Switch(config-vlan)# exit

Switch(config)# vlan 20
Switch(config-vlan)# name Finance
Switch(config-vlan)# exit

Switch(config)# vlan 30
Switch(config-vlan)# name HR
Switch(config-vlan)# exit

Note: As mentioned in the reading, some switches will automatically create a VLAN if you assign a port to it. However, it's a more reliable practice to create and name it manually first.

Step 2: Assign Ports to VLANs

Now, we'll configure the individual switch interfaces. For efficiency, we can use the interface range command to configure multiple ports at once.

// Assign ports F0/1 and F0/2 to the Marketing VLAN
Switch(config)# interface range fastEthernet 0/1 - 2
Switch(config-if-range)# switchport mode access
Switch(config-if-range)# switchport access vlan 10
Switch(config-if-range)# exit

// Assign ports F0/3 and F0/4 to the Finance VLAN
Switch(config)# interface range fastEthernet 0/3 - 4
Switch(config-if-range)# switchport mode access
Switch(config-if-range)# switchport access vlan 20
Switch(config-if-range)# exit

// Assign ports F0/5 and F0/6 to the HR VLAN
Switch(config)# interface range fastEthernet 0/5 - 6
Switch(config-if-range)# switchport mode access
Switch(config-if-range)# switchport access vlan 30
Switch(config-if-range)# exit

If you prefer a video walkthrough of this exact process, the second half of the Jeremy's IT Lab video demonstrates it.

3. Verifying Your VLAN Configuration

After configuration, you must always verify that the switch is operating as intended. The most useful command for this is show vlan brief.

Running show vlan brief on our switch would produce an output similar to this:

From Privileged EXEC mode (Switch#), you would type:

Switch# show vlan brief

The output would confirm:

• VLANs 10, 20, and 30 are active.
• They have the names we assigned (Marketing, Finance, HR).
• The correct ports (e.g., Fa0/1, Fa0/2) are listed next to their respective VLANs.
• All other unused ports remain in the default VLAN 1.

Conclusion

In this lesson, you moved beyond the default switch configuration to create a segmented Layer 2 network. This is a critical skill for building scalable, secure, and efficient networks. You now understand not just how to configure VLANs, but why they are so fundamental to network design.

Key Takeaways:

• Purpose of VLANs: To divide a single physical switch into multiple logical switches, thereby creating separate broadcast domains. This enhances security and performance.
• Access Ports: A switch port that belongs to a single VLAN and typically connects to an end device.
• Configuration Process:
  1. Create and name the VLAN from global config mode (vlan <id>, name <name>).
  2. Assign an interface as an access port to the VLAN (interface <id>, switchport mode access, switchport access vlan <id>).
• Verification: The show vlan brief command is your primary tool to confirm that VLANs are created and ports are assigned correctly.

In our next lesson, we will address a new challenge: how do you extend these VLANs across multiple switches? If a member of the HR team plugs into a different switch, how can they remain in the HR VLAN? The answer is trunking, and we'll explore how to configure 802.1Q trunk links to carry traffic for multiple VLANs between switches.