Understanding Vlans - Cisco Aironet 1100 Series Installation And Configuration Manual

Understanding VLANs

Understanding VLANs
A VLAN is a switched network that is logically segmented, by functions, project teams, or applications
rather than on a physical or geographical basis. For example, all workstations and servers used by a
particular workgroup team can be connected to the same VLAN, regardless of their physical connections
to the network or the fact that they might be intermingled with other teams. You use VLANs to
reconfigure the network through software rather than physically unplugging and moving devices or
wires.
A VLAN can be thought of as a broadcast domain that exists within a defined set of switches. A VLAN
consists of a number of end systems, either hosts or network equipment (such as bridges and routers),
connected by a single bridging domain. The bridging domain is supported on various pieces of network
equipment such as LAN switches that operate bridging protocols between them with a separate group
for each VLAN.
VLANs provide the segmentation services traditionally provided by routers in LAN configurations.
VLANs address scalability, security, and network management. You should consider several key issues
when designing and building switched LAN networks:
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You extend VLANs into a wireless LAN by adding IEEE 802.11Q tag awareness to the access point.
Frames destined for different VLANs are transmitted by the access point wirelessly on different SSIDs
with different WEP keys. Only the clients associated with that VLAN receive those packets. Conversely,
packets coming from a client associated with a certain VLAN are 802.11Q tagged before they are
forwarded onto the wired network.
Figure 12-1
segmentation with wireless devices connected.
Cisco Aironet 1100 Series Access Point Installation and Configuration Guide
12-2
LAN segmentation
Security
Broadcast control
Performance
Network management
Communication between VLANs
shows the difference between traditional physical LAN segmentation and logical VLAN
Chapter 12 Configuring VLANs
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