Virtual Local Area Networks (VLANs) B-1
v1.0, December 2007
Appendix B Virtual Local Area Networks (VLANs)
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 the appropriate port.
A virtual LAN (VLAN) is a local area network with a definition that maps workstations on some
basis other than geographic location (for example, by department, type of user, or primary
application). To enable traffic to flow between VLANs, traffic must go through a router, just as if
the VLANs 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 might not be. For example, all
marketing personnel might 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.
VLANs have a number of advantages:
• It is easy to do network segmentation. Users that communicate most frequently with each
other can be grouped into common VLANs, regardless of physical location. Each group’s
traffic is contained largely within the VLAN, reducing extraneous traffic and improving the
efficiency of the whole network.
• They are 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 from the wiring
closet.
• They provide increased performance. VLANs free up bandwidth by limiting node-to-node and
broadcast traffic throughout the network.
• They ensure enhanced ne twork security.VLANs create virtual boundaries that can be crossed
only through a router. So standard, router-based security measures can be used to restrict
access to each VLAN.