Virtual Local Area Networks
1-1
1
Virtual Local Area Networks
This chapter introduces the concepts of Virtual Local Area Networks (VLANs) and discusses the
central concepts of IEEE 802.1Q VLANs. This chapter also contains information on how to
contact Enterasys Networks for additional support related to VLANs.
1.1
DEFINING VLANs
A Virtual Local Area Network is a group of devices that function as a single Local Area Network
segment (broadcast domain). The devices that make up a particular VLAN may be widely
separated, both by geography and location in the network.
The creation of VLANs allows users located in separate areas or connected to separate ports to
belong to a single VLAN group. Users that are assigned to such a group will send and receive
broadcast and multicast traffic as though they were all connected to a common network. VLAN
aware switches isolate broadcast, multicast, and unknown traffic received from VLAN groups, so
that traffic from stations in a VLAN are confined to that VLAN.
When stations are assigned to a VLAN, the performance of their network connection is not
changed. Stations connected to switched ports do not sacrifice the performance of the dedicated
switched link to participate in the VLAN. As a VLAN is not a physical location, but a
membership, the network switches determine VLAN membership by associating a VLAN with a
particular port or frame type.
Figure 1-1
shows a simple example of a port based VLAN. Two buildings house the Sales and
Finance departments of a single company, and each building has its own internal network. The
stations in each building connect to a SmartSwitch in the basement. The two SmartSwitches are
connected to one another with a high speed link.
