4
C
HAPTER
1: I
NTRODUCTION
Figure 4
Bidirectional Load Balancing Failover
VLANs
A VLAN is a group of location-independent and topology-independent devices
that communicate as if they were on the same physical LAN. Network devices on
different LAN segments and of different media types can be members of the same
VLAN. Membership in a VLAN is determined by a VLAN tag that is transmitted
with the Ethernet frame for use by a switch.
With VLANs, you can define a network according to:
■
Organizational groups—For example, you can have one VLAN for the
Marketing department and one for the Finance department.
■
Application groups—For example, you can have one VLAN for e-mail users and
one for multimedia users.
Implementing VLANs on a network has these advantages:
■
It eases the change and movement of devices on IP networks.
With traditional IP networks, if users move to a different IP subnet, the IP
addresses of each workstation must be updated manually. With VLANs
installed, if an end station on VLAN 1 is moved to a port elsewhere on the
network, you need only to specify that the new port is on VLAN 1.
■
It helps to control traffic.
With traditional networks, congestion can be caused by broadcast traffic that is
directed to all network devices whether they require it or not. Each VLAN can
be set up to contain only those devices that need to communicate with each
other, increasing network efficiency.
■
It provides extra security.
Devices within each VLAN can communicate only with member 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.
The Dynamic
Access
technology multiple VLAN capability supports IEEE 802.1Q
VLAN tagging and works with any switch that is compliant with IEEE 802.1Q
specifications. See your Ethernet switch documentation for more information on
IEEE 802.1Q VLANs.
Server
Bidirectional
load balancing
Primary failure
Secondary failure
Clients
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¨
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Primary Secondaries
Primary Secondaries
Primary Secondaries
Switch
