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IEEE 802.1Q Virtual Local Area Network (VLAN) B-1
July 2005
Appendix B
IEEE 802.1Q Virtual Local Area Network (VLAN)
A Local Area Network (LAN) can generally be defined as a broadcast domain. Hubs, bridges or
switches in the same physical segment or segments connect all end node devices. End nodes can
communicate with each other without the need for a router. Routers connect LANs together,
routing the traffic to appropriate port.
A virtual LAN (VLAN) is a local-area network with a definition that maps workstations on some
other basis than geographic location (for example, by department, type of user, or primary
application). To communicate between VLANs, traffic must go through a router, just as if they
were on two separate LANs.
A VLAN is a group of PCs, servers and other network resources that behave as if they were
connected to a single, network segment — even though they may not be. For example, all
marketing personnel may be spread throughout a building. Yet if they are all assigned to a single
VLAN, they can share resources and bandwidth as if they were connected to the same segment.
The resources of other departments can be invisible to the marketing VLAN members, accessible
to all, or accessible only to specified individuals, depending on how the IT manager has set up the
VLANs.
The Advantages of VLANs
Easy to do network segmentation
Users communicate most frequently with each other can be grouped into common VLANs,
regardless of physical location. Each group's traffic is largely contained within the VLAN,
reducing extraneous traffic and improving the efficiency of the whole network.
Easy to manage
The addition of nodes, as well as moves and other changes, can be dealt with quickly and
conveniently from a management interface rather than the wiring closet.
Increased performance
VLANs free up bandwidth by limiting node-to-node and broadcast traffic throughout the network.
Enhanced network security
VLANs create virtual boundaries that can only be crossed through a router. So standard,
router-based security measures can be used to restrict access to each VLAN