Configuring Vlans; Overview; Vlan Fundamentals - HP 830 Series Configuration Manual

Configuring VLANs

Overview

Ethernet is a network technology based on the Carrier Sense Multiple Access/Collision Detect
(CSMA/CD) mechanism. The medium is shared, so collisions and excessive broadcasts are common on
an Ethernet. To address this issue, virtual LAN (VLAN) was introduced to break a LAN down into
separate VLANs. VLANs are isolated from each other at Layer 2. A VLAN is a bridging domain, and all
broadcast traffic is contained within it, as shown in
Figure 118 A VLAN diagram
A VLAN is logically divided on an organizational basis rather than on a physical basis. For example, all
workstations and servers used by a particular workgroup can be assigned to the same VLAN, regardless
of their physical locations.
VLAN technology delivers the following benefits:
Confining broadcast traffic within individual VLANs. This reduces bandwidth waste and improves
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network performance.
Improving LAN security. By assigning user groups to different VLANs, you can isolate them at Layer
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2. To enable communication between VLANs, routers or Layer 3 switches are required.
Flexible virtual workgroup creation. As users from the same workgroup can be assigned to the same
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VLAN regardless of their physical locations, network construction and maintenance is much easier
and more flexible.

VLAN fundamentals

To enable a network device to identify frames of different VLANs, a VLAN tag field is inserted into the
data link layer encapsulation. The format of VLAN-tagged frames is defined in IEEE 802.1Q- 1 999.
In the header of a traditional Ethernet data frame, the field after the destination MAC address and the
source MAC address is the Type field indicating the upper layer protocol type, as shown in
Figure 1 18.
119
Figure 1 19.