08-02-2010, 11:50 AM
virtual LAN, commonly known as a VLAN, is a group of hosts with a common set of requirements that communicate as if they were attached to the same broadcast domain, regardless of their physical location. A VLAN has the same attributes as a physical LAN, but it allows for end stations to be grouped together even if they are not located on the same network switch. Network reconfiguration can be done through software instead of physically relocating devicesVLANs are created to provide the segmentation services traditionally provided by routers in LAN configurations. VLANs address issues such as scalability, security, and network management. Routers in VLAN topologies provide broadcast filtering, security, address summarization, and traffic flow management. By definition, switches may not bridge IP traffic between VLANs as it would violate the integrity of the VLAN broadcast domain.The shift toward LAN switching as a replacement for local/departmental routers†and now even shared media devices (hubs) will only accelerate in the future. With the rapid decrease in Ethernet and Token Ring switch prices on a per-port basis, many more ambitious organizations are moving quickly toward networks featuring private port (single user/port) LAN switching architectures. Such a desktop switching architecture is ideally suited to VLAN implementation. To understand why private port LAN switching is so well suited to VLAN implementation, it is useful to review the evolution of segmentation and broadcast containment in the network over the past several years.
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http://www.3comnsc/200374.html
http://en.wikipediawiki/Virtual_LAN
http://www.micrel_PDF/Ethernet/White%20P...s%20wp.pdf