Qtech QSW-2900-24T-AC [69/209] Introduction to vlan

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Chapter 4 VLAN Configuration

4.1 Introduction to VLAN

4.1.1 VLAN Overview

Ethernet is a network technology based on the Carrier Sense Multiple Access/Collision Detect (CSMA/CD)

mechanism. As the medium is shared in an Ethernet, network performance may degrade as the number of hosts on

the network is increasing. If the number of the hosts in the network reaches a certain level, problems caused by

collisions, broadcasts, and so on emerge, which may cause the network operating improperly. In addition to the

function that suppresses collisions (which can also be achieved by interconnecting LANs), virtual LAN (virtual

LAN) can also isolate broadcast packets. VLAN divides a LAN into multiple logical LANs with each being a

broadcast domain. Hosts in the same VLAN can communicate with each other like in a LAN. However, hosts from

different VLANs cannot communicate directly. In this way, broadcast packets are confined to a single VLAN, as

illustrated in the following figure.

Figure 1 A VLAN diagram

A VLAN is not restricted by physical factors, that is to say, hosts that reside in different network segments

may belong to the same VLAN, users in a VLAN can be connected to the same switch, or span across multiple

switches or routers.

VLAN technology has the following advantages:

1) Broadcast traffic is confined to each VLAN, reducing bandwidth utilization and improving network performance.

2) LAN security is improved. Packets in different VLANs cannot communicate with each other directly. That is,

users in a VLAN cannot interact directly with users in other VLANs, unless routers or Layer 3 switches are used.

3) A more flexible way to establish virtual working groups. With VLAN technology, clients can be allocated to

different working groups, and users from the same group do not have to be within the same physical area, making

network construction and maintenance much easier and more flexible.