Cisco WLAN Controllers

Earlier, we discussed the lines of the Cisco Lightweight APs. The APs and wireless control system are two legs of a three-legged stool; WLAN controllers comprise the other.

WLAN controllers are the hub of systemwide WLAN operation. They are the devices on which information is stored and disseminated to thin APs. In return, environmental data is sent back to the WLAN controller for analysis and action. The information stored on the WLAN controllers includes:

• Voice and data service
• Security policies
• Intrusion prevention
• RF management
• QoS
• Mobility
• Thin AP configuration

WLAN controllers communicate with the thin APs over Layer 2 or Layer 3 infrastructure using the Lightweight Access Point Protocol (LWAPP). This protocol ensures that communication between WLAN controllers and thin APs is secure.

Cisco offers three series of WLAN controllers: the 2000 Series, the 4100 Series, and the 4400 Series.

The Cisco 2000 Series WLAN controller is targeted at small- to medium-sized enterprise applications. Its 2006 model is capable of controlling up to 6 thin APs. The 2000 is shown in Figure 1-10.


The Cisco 4100 Series WLAN controller is targeted at medium- to large-sized enterprise applications. Its three modelsthe 4112, 4124, and 4136offer support to 12, 24, or 26 thin APs, respectively. This series features dual Gigabit Ethernet uplinks for LAN connectivity. The 4100 Series is shown in Figure 1-11.


These WLAN controllers can detect and adapt to changes in the RF environment. This level of management affords the following functionality:

• Channels are dynamically assigned to optimize network coverage and lessen interference.
• The system detects interference and makes changes to the network to remedy the interference.
• Load balancing prevents a large number of users from overburdening a specific thin AP.
• The power outpoint of the thin APs is adjusted to detect and correct coverage holes.
• Power is automatically adjusted across the network to specific APs, based on changing network conditions.

WLAN controllers use up-to-date security features that include WPA2, WPA, WEP, multiple EAP types, and a VPN termination module for IPSec and Layer 2 Tunneling Protocol.

Other security features include:

• The capability to detect and avoid unwanted RF propagation.
• Intrusion prevention and location to ensure that rogue APs are not only found, but located.
• Network admission control that manages client access based on policies.

Because the WLAN controller operates at both Layer 2 and 3 levels, users can roam among APs, switches, and routed subnets without interruption in service. In addition, security and QoS information follows them, so the operation environment is consistent.