Wireless Network Management

In very large networks, a single wireless controller isn’t enough to manage all your APs. This type of scenario might call for the Cisco Wireless Control System (WCS). The WCS is a single point of management for up to 3000 lightweight APs and 1250 autonomous APs. The WCS runs on a Windows or Red Hat Linux server. To scale beyond 3000 APs, you would need the WCS Navigator. The WCS Navigator enables you to navigate between different wireless control systems. It is a manager of managers, so to speak. You can use the WCS Navigator to navigate between different WCS servers. You can then scale it up to 30,000 APs in a single deployment and support up to 20 WCS deployments, all within the WCS Navigator. There is also an additional appliance you can use, called the Cisco Wireless Location Appliance, as shown in Figure 10-13.


This is designed to do location tracking for Wi-Fi devices and RFID tags. It helps track thousands of devices.


Controller Discovery and Association

When a lightweight AP boots up, it cannot function without a controller. In this chapter, you will learn about the Lightweight Access Point Protocol (LWAPP) and the modes in which it can operate. You will also learn about how an AP finds controllers on the net- work, chooses one to join with, and then retrieves its configuration. In addition, you will look at the ways to provide redundancy for your AP in the event that a controller goes down. Finally, when an AP is joined with a controller, it can operate in certain modes that can be used for different reasons. You will learn these operational modes and when they are used.


Understanding the Different LWAPP Modes

LWAPP can operate in either Layer 2 LWAPP mode or Layer 3 LWAPP mode. The Layer 2 mode is considered out of date, and Cisco prefers and recommends Layer 3 mode. Layer 3 mode is the default LWAPP mode on most Cisco devices.

At a high level, and after the AP has an IP address, the phases of LWAPP operation include these:

Step 1. An AP sends an LWAPP discovery request message. This is a broadcast that is sent at Layer 2.

Step 2. Assuming that a controller is operating in Layer 2 LWAPP mode, the wireless LAN controller (WLC) receives the LWAPP discovery request and responds with an LWAPP discovery response message.

Step 3. The AP chooses a controller based on the response received and sends a join request.

Step 4. The WLC receiving the LWAPP join request responds to the AP join request with an LWAPP join response. This process is going to include a mutual au- thentication. An encryption key is created to secure the rest of the join process and any future LWAPP control messages.

Step 5. After the AP has joined the WLC, LWAPP messages are exchanged, and the AP initiates a firmware download from the WLC (if the AP and WLC have a version mismatch). If the onboard firmware of the AP is not the same as that of the WLC, the AP downloads firmware to stay in sync with the WLC. The firmware download mechanism utilizes LWAPP.

Step 6. After the WLC and AP match firmware revisions, the WLC provisions the AP with the appropriate settings. These settings might include service set identi- fiers (SSID), security parameters, 802.11 parameters such as data rates and sup- ported PHY types, radio channels, and power levels.

Step 7. After the provisioning phase is completed, the AP and WLC enter the LWAPP runtime state and begin servicing data traffic.

Step 8. During runtime operations, the WLC might issue various commands to the AP through LWAPP control messages. These commands might be provisioning commands or requests for statistical information that the AP collects and maintains.

Step 9. During runtime operations, LWAPP keepalive messages are exchanged be- tween the AP and WLC to preserve the LWAPP communication channel. When an AP misses a sufficient number of keepalive message exchanges, it at- tempts to discover a new WLC.