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 The Layer 2 mode is considered out of date, and Cisco prefers and recommends Layer 3 mode.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.

Wireless LAN Controllers

The entire design of the Wireless LAN Controllers is for scalability. The communication between a lightweight AP can happen over any type of Layer 2 or Layer 3 infrastructure using LWAPP. There are integrated controller platforms designed for installation in switches. The 3750-G actually comes as an integrated 2RU switch with either a 25 or 50 AP controller, as well as the WiSM and the WLCM. These are both modular controllers that can be installed in 6500 series switches or in Integrated Services Routers (ISR). There are also appliance-based controllers, which include the 44xx series WLC as well as the 2100 series WLC. Which controller you require depends on how many APs you need de- ployed. This can be anywhere from six to 300 access points per controller. This is a fixed value and can’t be upgraded via licensing. If you need to support more APs, you need an- other controller or a controller that supports more APs.


The Cisco 44xx Series WLC

The Cisco 44xx series Wireless LAN Controller, shown in Figure 10-8, is a standalone appliance.


It is designed to take up one rack unit. It has either two or four Gigabit Ethernet uplinks, and they use mini-GBIC FSG slots. It can support 12, 25, 50, or 100 APs, depending on the model. And it can support up to 5000 MAC addresses in its database.

The 4400 series has a 10/100 interface called a service port; it is used for SSH and SSL connections for management purposes. The service port can be used for out-of-band management, but it is not required to manage the device. You can manage the device via the controller’s logical management interface. There is also a console port that you can use to connect via HyperTerminal or Teraterm Pro.

Depending on the country you are in, power requirements vary, but the chassis has two power supply slots.

The controller code version used for the CCNA Wireless exam is version 5.x, and the AP runs the same version. It’s actually a requirement that they run the same version, so when an AP joins with a controller, the controller upgrades or downgrades the AP. The con- troller upgrades four APs at a time. The 4400 series can support up to 100 access points. So, a 4400 would upgrade ten APs at a time until they are all upgraded.


The Cisco WiSM

The Cisco WiSM, shown in Figure 10-10, is a services module that installs in the 6500 se- ries switch or 7600 series router with the Cisco Supervisor Engine 720.


It has the same functionality as the 4400 series standalone controllers; the difference is that it supports up to 300 APs. The WiSM supports 150 access points per controller, with each blade having two controllers. Thus, you can have a total of 300 access points. You can also cluster 12 of them into a mobility domain. This allows up to 7200 lightweight APs in a mobility domain.


The Cisco 2106 WLC

The Cisco 2106 Wireless LAN Controller, shown in Figure 10-11, is also a single-rack unit design with eight 10/100 Ethernet ports.


It can support up to six primary access points. It has an RJ-45 console port and two RJ-45 ports that support PoE. It has nearly all the same features as the 4400 series controllers but has eight built-in switch ports. You can expect to see this controller in a small branch environment.


The Cisco WLCM

The Wireless LAN Controller Module (WLCM), shown in Figure 10-12, is designed for the ISR routers. You would see this controller in a small office.


It has the same functionality as the 2106, but it does not have the directly connected AP and console port. It supports six APs. The WLCM-Enhanced (WLCM-E) supports eight or 12 APs, depending on which module you get.

Of course, some limitations apply. Most of the features are similar to the 4000 series:

• LWAPP

• RF control

• The ability to be a DHCP server

• Layer 2 security

The differences are things such as the following:

• Lack of PoE ports

• The number of APs supported

• The LWAPP modes supported

Wireless LAN Controller Summary

Table 10-3 summarizes the Cisco Wireless LAN Controller models.