Operation Manual – VLAN
H3C S3100 Series Ethernet Switches Chapter 1 VLAN Overview
1-2
communicate with each other directly but need the help of network layer devices, such
as routers and Layer 3 switches.
Figure 1-1 illustrates a VLAN implementation.
Figure 1-1 A VLAN implementation
1.1.2 Advantages of VLANs
Compared with traditional Ethernet technology, VLAN technology delivers the following
benefits:
z Confining broadcast traffic within individual VLANs. This saves bandwidth and
improves network performance.
z Improving LAN security. By assigning user groups to different VLANs, you can
isolate them at Layer 2. To enable communication between VLANs, routers or
Layer 3 switches are required.
z Flexible virtual workgroup creation. As users from the same workgroup can be
assigned to the same VLAN regardless of their physical locations, network
construction and maintenance is much easier and more flexible.
1.1.3 VLAN Fundamentals
I. VLAN tag
To enable a Layer-2 switch 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 issued by IEEE in 1999.
In the header of a traditional Ethernet data frame, the field after the destination MAC
address and the source MAC address (DA&SA) is the Type field indicating the upper
layer protocol type, as shown in
Figure 1-2.
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