VLAN, QoS, and Proxy Mobile IP
VLAN features

LANs are increasingly being divided into workgroups connected through common backbones to form virtual LAN (VLAN) topologies. VLANs enable efficient traffic separation, provide better bandwidth utilization, and alleviate scaling issues by logically segmenting the physical local-area network (LAN) infrastructure into different subnets so that packets are switched only between ports within the same VLAN. When combined with central configuration management support, VLANs facilitate workgroups and client/server additions and changes. Some common reasons why a company might have VLANs:

  • Security – Separating systems that have sensitive data from the rest of the network decreases the chances that people will gain access to information they are not authorized to see.
  • Departments/Specific job types – Companies may want VLANs set up for departments that are heavy network users (such as multimedia or engineering), or a VLAN across departments that is dedicated to specific types of employees (such as managers or sales people).
  • Broadcasts/Traffic flow – Since a principle element of a VLAN is the fact that it does not pass broadcast traffic to nodes that are not part of the VLAN, it automatically reduces broadcasts. Access lists (ACL) provide the network administrator with a way to control who sees what network traffic.

The Cisco Aironet APs only support the 802.1Q Trunking protocol standard. Cisco switches and routers can support both the pre-standard Inter-Switch Link (ISL) protocol and 802.1Q, depending on the model and IOS image. Switches will not allow different VLANs to talk to one another. A router will be needed to allow different VLANs to communicate to each other. The Cisco Aironet APs can be configured with 16 different VLANs for system design flexibility.

WLANs can now fit nicely into the larger network because VLANs have been enabled on the APs. This allows WLAN users to roam from access point to access point maintaining connectivity to the proper VLAN. Figure shows a sample topology using the VLAN features.