VLAN Configuration Essentials: Segmenting Your Network

Virtual Local Area Networks (VLANs) are a fundamental technology for network segmentation. They allow you to logically divide a physical network into multiple broadcast domains, improving security, performance, and management. In this guide, we'll explore how to configure VLANs on Cisco switches.

A VLAN is a logical grouping of devices within the same broadcast domain, regardless of their physical location. Key benefits include:

• Improved security through network segmentation
• Better performance by reducing broadcast traffic
• Simplified network management and troubleshooting
• Flexibility in network design and device placement

Step 1: Create a VLAN

To create a VLAN, enter global configuration mode and use the vlan command:

Switch(config)# vlan 10
Switch(config-vlan)# name SALES
Switch(config-vlan)# exit

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

Step 2: Assign ports to VLANs

After creating VLANs, assign switch ports to them:

Switch(config)# interface range fastethernet 0/1 - 10
Switch(config-if-range)# switchport mode access
Switch(config-if-range)# switchport access vlan 10
Switch(config-if-range)# exit

Switch(config)# interface range fastethernet 0/11 - 20
Switch(config-if-range)# switchport mode access
Switch(config-if-range)# switchport access vlan 20
Switch(config-if-range)# exit

Trunk ports carry traffic for multiple VLANs between switches. Configure a trunk port with the following commands:

Switch(config)# interface gigabitethernet 0/1
Switch(config-if)# switchport mode trunk
Switch(config-if)# switchport trunk allowed vlan 10,20
Switch(config-if)# exit

Use these commands to verify your VLAN configuration:

Switch# show vlan brief
Switch# show interfaces trunk
Switch# show interfaces fastethernet 0/1 switchport

• Always change the native VLAN from VLAN 1 for security
• Use descriptive VLAN names for easier management
• Document your VLAN assignments and IP schemes
• Disable unused ports and assign them to an unused VLAN
• Implement Voice VLANs for IP phones to separate voice and data traffic

VLANs are a powerful tool for network segmentation and management. By properly configuring VLANs and trunk ports, you can create a more secure, efficient, and manageable network infrastructure. In the next article, we'll explore inter-VLAN routing techniques.