Tp-Link TL-SG108PE — преимущества и особенности виртуальных локальных сетей (VLAN) [33/48]

Chapter 7 VLAN

The traditional Ethernet is a data network communication technology based 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 Lay3 switch, etc.

The following figure illustrates a VLAN implementation.

Figure 7-1 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 do not need to change its network configuration.