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Benefits and Restrictions
12.2.3 Other VLAN Strategies
VLANs may also be created by a variety of addressing schemes, including the recognition of
groups of MAC addresses or types of traffic. One of the best-known VLAN-like schemes is the use
of IP Subnets to divide networks into smaller subnetworks.
12.3 BENEFITS AND RESTRICTIONS
The primary benefit of the 802.1Q VLAN technology is that it provides localization of traffic. This
function also offers improvements in security and performance to stations assigned to a VLAN.
While the localization of traffic to VLANs can improve security and performance, it imposes some
restrictions on network devices that participate in the VLAN. Through the use of Filtering
Database IDs (FIDs) security can be implemented to enable or prevent users from one or more
VLANs from communicating with each other.
One or more VLANs can be assigned to a FID so that all the users that share a common FID can
communicate with each other regardless of their VLAN affiliation. However, for the sake of
security, the members of one FID cannot communicate with the members of another FID.
To set up a VLAN, all the network switch devices that are assigned to the VLAN must support the
IEEE 802.1Q specification for VLANs. Before you attempt to implement a VLAN strategy, ensure
that the switches under consideration support the IEEE 802.1Q specification.
12.4 VLAN TERMS
To fully understand the operation and configuration of port based VLANs, it is essential to
understand the definitions of several key terms.
VLAN ID
A unique number (between 1 and 4094) that identifies a particular VLAN.
VLAN Name
A 32-character alphanumeric name associated with a VLAN ID. The VLAN Name is intended to
make user-defined VLANs easier to identify and remember.
Filtering Database Identifier (FID)
Addressing information that the device learns about a VLAN is stored in the filtering database
assigned to that VLAN. Several VLANs can be assigned to the same FID to allow those VLANs to
share addressing information. This enables the devices in the different VLANs to communicate
with each other when the individual ports have been configured to allow communication to occur.
The configuration is accomplished using the Local Management VLAN Forwarding Configuration
screen. By default a VLAN is assigned to the FID that matches its VLAN ID.
12-4
VLAN Operation and Network Applications
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