Operation Manual – VLANH3C S5100-SI/EI Series Ethernet Switches Chapter 1 VLAN Overview1-1Chapter 1 VLAN OverviewThis chapter covers these topics:z VLAN Overviewz Port-Based VLANz Protocol-Based VLAN1.1 VLAN Overview1.1.1 Introduction to VLANThe traditional Ethernet is a broadcast network, where all hosts are in the samebroadcast domain and connected with each other through hubs or switches. Hubs andswitches, which are the basic network connection devices, have limited forwardingfunctions.z A hub is a physical layer device without the switching function, so it forwards thereceived packet to all ports except the inbound port of the packet.z A switch is a link layer device which can forward a packet according to the MACaddress of the packet. However, when the switch receives a broadcast packet oran unknown unicast packet whose MAC address is not included in the MACaddress table of the switch, it will forward the packet to all the ports except theinbound port of the packet.The above scenarios could result in the following network problems.z Large quantity of broadcast packets or unknown unicast packets may exist in anetwork, wasting network resources.z A host in the network receives a lot of packets whose destination is not the hostitself, causing potential serious security problems.Isolating broadcast domains is the solution for the above problems. The traditional wayis to use routers, which forward packets according to the destination IP address anddoes not forward broadcast packets in the link layer. However, routers are expensiveand provide few ports, so they cannot split the network efficiently. Therefore, usingrouters to isolate broadcast domains has many limitations.The Virtual Local Area Network (VLAN) technology is developed for switches to controlbroadcasts in LANs.A VLAN can span multiple physical spaces. This enables hosts in a VLAN to be locatedin different physical locations.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 in the traditional Ethernet way. However, hosts in different VLANs cannot
