A virtual local area network (VLAN) is a group of logical devices and users that are not limited by their physical location， but can be organized according to functional， departments and applications, and communicate with each other as if they were in the same network segment.VLAN is a relatively new technology that works in layer 2 and layer 3 of the OSI reference model. A VLAN is a broadcast domain, and communication between VLAN is accomplished through layer 3 routers.Compared with the traditional LAN technology, VLAN technology is more flexible, it has the following advantages: network equipment to move, add and modify the management overhead reduced, can control broadcast activities, can improve network security.