3Com SuperStack II, Manual

Page: 164 / 248

164 C
HAPTER
6: V
IRTUAL
LAN
S
(VLAN
S
)
What are VLANs?
A VLAN is a flexible group of devices that can be located anywhere in a
network, but they communicate as if they are on the same physical
segment. With VLANs, you can segment your network without being
restricted by physical connections — a drawback of traditional network
design. As an example, with VLANs you can segment your network
according to:
■
Departmental groups — For example, you can have one VLAN for
the Marketing department, another for the Finance department, and
another for the Development department.
■
Hierarchical groups — For example, you can have one VLAN for
directors, another for managers, and another for general staff.
■
Usage groups — For example, you can have one VLAN for users of
e-mail, and another for users of multimedia.
Benefits of VLANs
The main benefit of VLANs is that they provide a network segmentation
system that is far more flexible than any traditional network. Using VLANs
also provides you with three other benefits:
■
It eases the change and movement of devices on IP networks
With traditional IP networks, network administrators spend much of
their time dealing with moves and changes. If users move to a
different IP subnet, the IP addresses of each endstation must be
updated manually.
With a VLAN setup, if an endstation in VLAN 1 is moved to a port in
another part of the network, you only need to specify that the new
port forwards VLAN 1 traffic.
■
It provides extra security
Devices within each VLAN can only communicate directly with devices
in the same VLAN. If a device in VLAN 1 needs to communicate with
devices in VLAN 2, the traffic needs to pass through a routing device
or Layer 3 switch.
■
It helps to control broadcast traffic
With traditional networks, congestion can be caused by broadcast
traffic that is directed to all network devices whether they require it or
not. VLANs increase the efficiency of your network because each
VLAN can be set up to contain only those devices that need to
communicate with each other.