Qtech QSW-3200-28FC [36/136] Chapter 3 vlan configuration

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Chapter 3 VLAN CONFIGURATION

3.1 Brief introduction of VLAN

VLAN (Virtual Local Area Network ) is a technology divided devices in LAN logically not

physically into network interfaces to realize virtual workgroup. IEEE promulgated IEEE 802.1Q

protocol standard draft to realize standardized VLAN.

VLAN technology allows network administrator to divide a physical LAN into different

broadcast domain or VLAN logically. Each VLAN contain a group of computer station with the

same need to possess the same attribute with the LAN formed physically. But it is divided

logically not physically, so each working station of the same VLAN need not be in the same

physical space. Broadcast and unicast flow in a VLAN will not transfer to other VLAN, which is

helpful to control the flow, reduce device cost, predigest network management and improve

network security. Following are VLAN features:

 Flow control helped by VLAN

In traditional network, large number of broadcast data is sent to all network devices to cause

network congestion. VLAN can configure the intercommunicated devices in each VLAN to

reduce broadcast to improve network efficiency.

 provides higher security

Device in one VLAN can only intercommunicate with the device in the same VLAN. For

example, devices in R&D department can intercommunicate with production department only

by the routing device, which greatly improved system security for the two departments cannot

intercommunicate directly.

3.2 VLAN interface type

System supports IEEE 802.1Q which possesses two types of VLAN interfaces. One is tagged,

and the other is untagged.

Tagged interface can ad VLAN ID, priority and other VLAN information to the head of the

packet which is out of the interface. If the packet has included IEEE 802.1Q information when

entering the switch, the mark information will not be changed; if the packet has not includes

IEEE 802.1Q mark information, system will determine the VLAN it belongs to according to the

default VLAN ID of the receiving interface. Network devices supported IEEE 802.1Q will

determine whether or not to transmit this packet by the VLAN information in the mark.

Untagged interface can drop the mark information from all the packets which are out of the

interface. When a frame is out of a untagged interface, it will not contain IEEE 802.1Q mark

information. The function of dropping the mark makes the packet can be transferred from the

network device supported mark to the one which doesn’t support it.

Now, only the switch supported IEEE 802.1Q can be recognize IEEE 802.1Q frame so only a

port linking to a switch supported IEEE 802.1Q can be configured to be Tagged port.

3.3 Default VLAN

There is a default VLAN of production, which possesses following features:

 The name of this VLAN is Default which can be modified.

 It includes all ports which can be added and deleted.

 All the port mode of default VLAN is untagged which can be modified to be tagged.

 VLAN ID of default VLAN is 1 which cannot be deleted.