Operation Manual – VLANH3C S7500 Series Ethernet Switches Chapter 1 VLAN Overview1-1Chapter 1 VLAN OverviewThis chapter covers the following topics:z VLAN Overviewz Port-Based VLANz Protocol-Based VLAN1.1 VLAN Overview1.1.1 Introduction to VLANThe traditional Ethernet is a flat network, where all hosts are in the same broadcastdomain and connected with each other through hubs or switches. A hub is a physicallayer device without the switching function, so it forwards the received packet to allports. A switch is a link layer device which can forward the packet according to the MACaddress of the packet. However, when the switch receives a broadcast packet or anunknown unicast packet whose MAC address is not included in the MAC address tableof the switch, it will forward the packet to all the ports except the inbound port of thepacket.In the above scenarios, a host in the network receives a lot of packets whosedestination is not the host itself, wasting plenty of bandwidth resources and causingpotential serious security problems as well.The traditional way of isolating broadcast domains is to use routers. However, routersare expensive and provide few ports, so they cannot subnet the network particularly.The Virtual Local Area Network (VLAN) technology is developed for switches to controlbroadcast 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 VLANcommunicate with each other as if they are in a LAN. However, hosts in different VLANscannot communicate with each other directly. Figure 1-1 illustrates a VLANimplementation.
