Operation Manual – VLANH3C S3100 Series Ethernet Switches Chapter 1 VLAN Overview1-2communicate with each other directly but need the help of network layer devices, suchas routers and Layer 3 switches. Figure 1-1 illustrates a VLAN implementation.Figure 1-1 A VLAN implementation1.1.2 Advantages of VLANsCompared with traditional Ethernet technology, VLAN technology delivers the followingbenefits:z Confining broadcast traffic within individual VLANs. This saves bandwidth andimproves network performance.z Improving LAN security. By assigning user groups to different VLANs, you canisolate them at Layer 2. To enable communication between VLANs, routers orLayer 3 switches are required.z Flexible virtual workgroup creation. As users from the same workgroup can beassigned to the same VLAN regardless of their physical locations, networkconstruction and maintenance is much easier and more flexible.1.1.3 VLAN FundamentalsI. VLAN tagTo enable a Layer-2 switch to identify frames of different VLANs, a VLAN tag field isinserted 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 MACaddress and the source MAC address (DA&SA) is the Type field indicating the upperlayer protocol type, as shown in Figure 1-2.
