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7-2 CHAPTER 7: VIRTUAL LANS
Benefits of VLANs
Implementing VLANs on your network has three main
advantages:
■ It eases the change and movement of devices on
networks.
■ It helps to control broadcast traffic.
■ It provides extra security.
How VLANs Ease Change and Movement
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 manu-
ally.
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 is in VLAN 1,
and this is something that can be done remotely if
you have 3Com’s Transcend Enterprise Manager for
Windows (v6.0 and above).
How VLANs 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.
How VLANs Provide Extra Security
Devices within each VLAN can only communicate
with devices in the same VLAN. If a device in VLAN 1
needs to communicate with devices in VLAN 2, the
traffic must cross a router. Routers have filtering and
security features to block unauthorized access.
Figure 7-1 shows a network configured with three
VLANs—one for each of the departments that access
the network. The membership of VLAN 1 is restricted
to ports 1, 2, 3, 4 and 5 of Switch A; membership of
VLAN 2 is restricted to ports 4, 5, 6, 7 and 8 of Switch
B while VLAN 3 spans both Switches containing ports
6, 7, 8 of Switch A and 1, 2, 3 of Switch B.
In this simple example, each of these VLANs can be
seen as a ’broadcast domain’—physical LAN seg-
ments that are not constrained by their physical loca-
tion.
Specific configurations using the Switch are shown
later in this chapter.