Specifications

Optimizing Performance
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EIO0000000051 6/2010
Virtual Local Area Network (VLAN)
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
unintended VLANs, provides security 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.