User`s guide

Chapter 2: Virtual Local Area Networks
2-4 Port Based VLAN User’s Guide
2.3 BENEFITS AND RESTRICTIONS
The primary benefit of the port based VLAN technology is the
localization of traffic that it provides. This function can offer
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. If a switch is operating in the “secure mode,” a
group of users assigned to a single VLAN can communicate with one
another freely, but cannot communicate with users on other VLANs
without the services of a Network Layer (OSI Layer 3) routing device to
make the connection between the VLANs. In the “open” mode, this
restriction does not apply.
In order to set up a VLAN, all the network switch devices that are
assigned to the VLAN must support the prestandard IEEE 802.1Q
specification for port based VLANs. Before you attempt to implement a
VLAN strategy, ensure that the switches under consideration support the
802.1Q specification.
2.4 VLAN TERMS
To fully understand the operation and configuration of port based VLANs,
it is essential to understand the meanings of several key terms.
VLAN ID
A unique number (between 1 and 4095) 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.
Tag Header (VLAN Tag)
A field within a frame that identifies the VLAN the frame has been
classified into. The Tag Header is inserted into the frame directly after the
Source MAC address field. Twelve bits of the Tag Header are the VLAN
ID. The remaining bits are other control information.