virtual LAN

Virtual LAN

(networking)Software defined groups of host on a local area network (LAN) that communicate as if they were on thesame wire, even though they are physically on different LAN segments throughout a site. To define a virtual LAN, thenetwork administrator uses a virtual LAN management utilityto establish membersip rules that determine which hostss arein a specific virtual LAN. Many models may exist but two seemto dominate:

(1) Vitual Segment (or Port-Group) Virtual LAN. These areswitched at the data link layer (OSI layer 2). Virtualsegments turn an arbitrary number of physical segments into asingle virtual segment that funtions as a self-containedtraffic domain.

(2) Virtual Subnet Virtual LAN: These are switched at theNetwork Layer (OSI layer 3). Subnet-oriented virtual LANsare based on subnet addresses used by IP, IPX, and othernetwork layer protocols to normally identify physicalnetworks. Administrators assign one subnet address to anumber of switch ports (which may be on different switchesand over a backbone). Once identified as a virtual subnet,the selected LANs function as a bridge group - traffic isbridged at Layer 2 within the virtual subnet and routed atLayer 3 between virtual subnets.

virtual LAN

Also called a "VLAN," it is a logical subgroup within a local area network that is created via software rather than manually moving cables in the wiring closet. It combines user stations and network devices into a single unit regardless of the physical LAN segment they are attached to and allows traffic to flow more efficiently within populations of mutual interest.

VLANs are implemented in port switching hubs and LAN switches and generally offer proprietary solutions. VLANs reduce the time it takes to implement moves, adds and changes.

VLANs function at layer 2. Since their purpose is to isolate traffic within the VLAN, in order to bridge from one VLAN to another, a router is required. The router works at the higher layer 3 network protocol, which requires that network layer segments are identified and coordinated with the VLANs. This is a complicated job, and VLANs tend to break down as networks expand and more routers are encountered. The industry is working towards "virtual routing" solutions, which allows the network manager to view the entire network as a single routed entity. See 802.1q.

The VLAN
Virtual LANs solve the problem of containing traffic within workgroups that are geographically dispersed. They allow moves, adds and changes to be performed via software at a console rather than manually changing cables in the wiring closet.