Learn about Virtual Local Area Networks (VLANs) and trunking protocols through interactive visualizations. Understand how VLANs segment networks, improve security, and optimize traffic flow.
A Virtual Local Area Network (VLAN) is a logical grouping of network devices that behave as if they are on the same physical network segment, even if they are physically located on different network segments. VLANs allow network administrators to segment a single physical network into multiple logical networks.
VLANs work by tagging network frames with a VLAN identifier (VLAN ID). This tagging allows switches to determine which VLAN a frame belongs to and forward it only to ports that are members of that VLAN. The IEEE 802.1Q standard defines the VLAN tagging mechanism.
VLANs isolate traffic between different departments or user groups, preventing unauthorized access to sensitive data. Devices in one VLAN cannot directly communicate with devices in another VLAN without a router.
VLANs reduce network congestion by limiting broadcast domains. Broadcast traffic is only forwarded within the VLAN, reducing unnecessary traffic on other network segments.
VLANs allow network administrators to logically group devices regardless of their physical location. Users can be moved between VLANs without changing physical connections.
VLANs simplify network administration by allowing centralized management of network policies and security rules. Changes can be made through software configuration rather than physical rewiring.
Trunking is a technique used to carry traffic from multiple VLANs over a single physical link. A trunk port can carry traffic for all configured VLANs, identified by VLAN tags in the frame headers. This allows switches to connect to each other and carry traffic for multiple VLANs efficiently.
When a switch receives a frame from an access port, it associates the frame with the VLAN configured for that port.
The switch adds an 802.1Q tag to the frame header containing the VLAN ID before forwarding it to a trunk port.
The tagged frame is transmitted over the trunk link to another switch, which can identify the VLAN based on the tag.
The receiving switch removes the VLAN tag and forwards the frame only to ports that are members of the specified VLAN.
VLANs are configured on network switches through various methods. The most common approach is to assign switch ports to specific VLANs, creating access ports. Trunk ports are configured to carry traffic for multiple VLANs.
Determine the number of VLANs needed and assign VLAN IDs. Plan which devices will belong to each VLAN based on department, function, or security requirements.
Use switch commands to create VLANs and assign descriptive names. For example:
vlan 10
name Sales
Configure switch ports as access ports and assign them to specific VLANs. For example:
interface fastethernet 0/1
switchport mode access
switchport access vlan 10
Set up trunk ports to carry traffic for multiple VLANs. For example:
interface fastethernet 0/24
switchport mode trunk
switchport trunk allowed vlan 10,20,30