Virtual Local Area Network (VLAN)
Original instructions
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Introduction
Use VLANs to divide a larger network into smaller virtual groups of devices, and to split a switch into many virtual network switches. VLANs permit the creation of logically separate groups of network devices, without having to physically re-wire those devices.
When a switch receives a message directed to a specific VLAN, it forwards that message only to the switch ports connected to devices that are members of that VLAN. The switch does not send the message to other ports.
A VLAN reduces network traffic, blocks multicast and broadcast traffic from other VLANs, provides separation between VLANs, and improves system performance.
VLAN Types
Depending upon the switch features, there many different ways to define and implement VLANs:
Tagging type
Mapping rule
Description
Explicit (VLAN tag in Ethernet packet)
Tag based
Each VLAN group is assigned a unique VLAN ID, which is included in each Ethernet packet. The switch forwards packets based on VLAN ID.
Implicit (no VLAN tag in Ethernet packet)
Port based
Switch ports are assigned to different VLANs, when the switch is configured (see example, below.)
MAC based
A switch maps VLAN group membership—and forwards Ethernet frames—based on device MAC address.
Protocol based
A switch maps VLAN group membership—and forwards Ethernet frames—based on message protocol.
IP-subnet based
A switch maps VLAN group membership—and forwards Ethernet frames—based on IP subnet portion of the target address.
Example
In the port-based VLAN example, below, switch ports 1, 2, and 3 are assigned to VLAN A, while switch ports 4, 5, and 6 are assigned to VLAN B:
NOTE: A single port can be a member of multiple VLANs.