What is a VLAN?
A VLAN (Virtual Local Area Network) is a logical grouping of devices within a network, segmented as if they were on separate physical networks — even though they may share the same switch.
With VLANs, devices can communicate within their group, while traffic to other VLANs is controlled via routers or Layer 3 switches.
Why Use VLANs?
- Network Segmentation-Isolate different departments or functions.
- Enhanced Security-Limit broadcast domains and unauthorized access.
- Improved Performance-Reduce broadcast traffic by containing it within a VLAN.
- Flexibility Easily manage network resources without changing physical layouts.
How Does VLAN Work?
Without VLANs
All devices connected to the same switch are part of a single broadcast domain. Broadcast traffic is sent to every port — causing unnecessary congestion.
With VLANs
Switch ports are assigned to VLANs, limiting broadcast traffic to only those ports in the same VLAN. This logical segmentation keeps networks organized and efficient.
Types of VLANs
| Type | Purpose |
|---|---|
| Default VLAN | Usually VLAN 1 — preconfigured on switches. |
| Data VLAN | Carries user-generated data traffic. |
| Voice VLAN | Dedicated for VoIP traffic to prioritize voice packets. |
| Management VLAN | Used for switch management (remote access). |
| Native VLAN | Used for untagged traffic on a trunk port. |
VLAN Tagging Explained
To allow multiple VLANs over a single link (trunk), VLAN tagging is used.
- IEEE 802.1Q Standard- Inserts a tag into Ethernet frames to identify VLANs.
- Access Port- Carries traffic for one VLAN (untagged).
- Trunk Port- Carries traffic for multiple VLANs (tagged).
Each department's devices are connected to the same switch but segmented via VLANs. Communication between VLANs is only possible through a router — enhancing security and control.
Real-World Example of VLAN Use
Imagine a company with three departments:
- HR (VLAN 10)
- Finance (VLAN 20)
- IT (VLAN 30)
Each department's devices are connected to the same switch but segmented via VLANs. Communication between VLANs is only possible through a router — enhancing security and control.
VLAN vs Subnet — What's the Difference?
| VLAN | Subnet |
|---|---|
| Works at Layer 2 (Data Link) | Works at Layer 3 (Network) |
| Logical grouping of devices | IP-based grouping of devices |
| Controlled by switches | Controlled by routers |
| Can span multiple subnets | Defines IP address range |
VLAN Configuration Basics (Cisco Example)
Subnetting has practical applications across various scenarios:
Switch(config)# vlan 10
Switch(config-vlan)# name HR
Switch(config)# interface fa0/1
Switch(config-if)# switchport mode access
Switch(config-if)# switchport access vlan 10Conclusion
VLANs are essential for modern network design, providing flexibility, control, and improved performance. Whether you're segmenting departments or prioritizing traffic types, understanding how VLANs work is a key skill for any network professional.
Frequently Asked Questions
Can devices on different VLANs communicate?
Only if routing is configured between VLANs (Inter-VLAN Routing).
What is a VLAN trunk?
A trunk allows traffic from multiple VLANs to pass over a single network link.
Is VLAN a security feature?
VLAN improves security by isolating traffic but should be combined with other measures like ACLs and firewalls.