509
B
B. Configuration Examples
This appendix contains information about how to configure the following features:
•Virtual Local Area Networks (VLANs) on page 509
•Access Control Lists (ACLs) on page 511
•Differentiated Services (DiffServ) on page 514
•802.1X on page 518
•MSTP on page 521

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.