Tp-Link T2500-28TC V2 [81/342] Chapter 6 vlan

Chapter 6 VLAN

The traditional Ethernet is a data network communication technology basing on CSMA/CD

(Carrier Sense Multiple Access/Collision Detect) via shared communication medium. Through

the traditional Ethernet, the overfull hosts in LAN will result in serious collision, flooding

broadcasts, poor performance or even breakdown of the Internet. Though connecting the

LANs through switches can avoid the serious collision, the flooding broadcasts cannot be

prevented, which will occupy plenty of bandwidth resources, causing potential serious security

problems.

A Virtual Local Area Network (VLAN) is a network topology configured according to a logical

scheme rather than the physical layout. The VLAN technology is developed for switches to

control broadcast in LANs. By creating VLANs in a physical LAN, you can divide the LAN into

multiple logical LANs, each of which has a broadcast domain of its own. Hosts in the same

VLAN communicate with one another as if they are in a LAN. However, hosts in different VLANs

cannot communicate with one another directly. Therefore, broadcast packets are limited in a

VLAN. Hosts in the same VLAN communicate with one another via Ethernet whereas hosts in

different VLANs communicate with one another through the Internet devices such as Router,

the Layer3 switch, etc. The following figure illustrates a VLAN implementation.

Figure 6-1 VLAN implementation

Compared with the traditional Ethernet, VLAN enjoys the following advantages.

1. Broadcasts are confined to VLANs. This decreases bandwidth utilization and improves

network performance.

2. Network security is improved. VLANs cannot communicate with one another directly. That

is, a host in a VLAN cannot access resources in another VLAN directly, unless routers or

Layer 3 switches are used.

3. Network configuration workload for the host is reduced. VLAN can be used to group

specific hosts. When the physical position of a host changes within the range of the VLAN,

you need not to change its network configuration.

A VLAN can span across multiple switches, or even routers. This enables hosts in a VLAN to be

dispersed in a looser way. That is, hosts in a VLAN can belong to different physical network