CCNA Wireless 200-355 Official Cert Guide (2016)

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1. Which two of the following things are bound together when a new WLAN is created?

a. VLAN

b. AP

c. Controller interface

d. SSID

2. What is the maximum number of WLANs you can configure on a Cisco wireless controller?

a. 8

b. 16

c. 512

d. 1024

3. What is the maximum number of WLANs that can be enabled on a Cisco lightweight AP?

a. 8

b. 16

c. 512

d. 1024

4. Which one of the following is a limiting factor when multiple WLANs are offered on an AP and its radio channel?

a. The speed of the controller interface

b. The airtime used for each WLAN’s beacons

c. Co-channel interference between WLANs on the AP

d. The number of APs joined to the controller

5. Which of the following parameters are necessary when creating a new WLAN with the controller GUI? (Choose all that apply.)

a. SSID

b. VLAN number

c. Interface

d. BSSID

e. IP subnet

6. The WLAN ID number is advertised to wireless clients. True or false?

a. True

b. False

Foundation Topics

WLAN Overview

Recall from Chapter 8, “Understanding Cisco Wireless Architectures,” that a wireless LAN controller and an access point work in concert to provide network connectivity to wireless clients. From a wireless perspective, the AP advertises a service set identifier (SSID) for the client to join. From a wired perspective, the controller connects to a virtual LAN (VLAN) through one of its dynamic interfaces. To complete the path between the SSID and the VLAN, as illustrated in Figure 15-1, you must first define a WLAN on the controller.

Figure 15-1 Connecting Wired and Wireless Networks with a WLAN

The controller will bind the WLAN to one of its interfaces and then push the WLAN configuration out to all of its APs by default. From that point on, wireless clients will be able to learn about the new WLAN and will be able to probe and join the new basic service set (BSS).

Like VLANs, you can use WLANs to segregate wireless users and their traffic into logical networks. Users associated with one WLAN cannot cross over into another one unless their traffic is bridged or routed from one VLAN to another through the wired network infrastructure.

Before you begin to create new WLANs, it is usually wise to plan your wireless network first. In a large enterprise, you might have to support a wide variety of wireless devices, user communities, security policies, and so on. You might be tempted to create a new WLAN for every occasion, just to keep groups of users isolated from each other or to support different types of devices. Although that is an appealing strategy, you should be aware of two limitations:

Cisco controllers support a maximum of 512 WLANs, but only 16 of them can be actively configured on an AP. The Cisco 2504 Wireless Controller is limited to a maximum of 16 WLANs.

Advertising each WLAN uses up valuable airtime.

Every AP must broadcast beacon management frames at regular intervals to advertise the existence of a BSS. Because each WLAN is bound to a BSS, each WLAN must be advertised with its own beacons. Beacons are normally sent ten times per second, or once every 100 ms, at the lowest mandatory data rate. The more WLANs you have created, the more beacons you will need to announce them.

Even further, the lower the mandatory date rate, the more time each beacon will take to be transmitted. The end result is this: If you create too many WLANs, a channel can be starved of any usable airtime. Clients will have a hard time transmitting their own data because the channel is overly busy with beacon transmissions. As a rule of thumb, always limit the number of WLANs to five or fewer; a maximum of three WLANs is best.

Configuring a WLAN

By default, a controller has no configuration and therefore no WLANs. Before you create a new WLAN, think about the following parameters it will need to have:

SSID

Controller interface and VLAN number

Type of wireless security needed

As you work through this chapter, you will create the appropriate dynamic controller interface to support the new WLAN, then you will enter the necessary WLAN parameters. Both the centralized and converged wireless architectures are covered, as you can use a similar GUI for each type of WLC.

Configuring a RADIUS Server

If your new WLAN will use a security scheme that requires a RADIUS server, you need to define the server first. On a centralized controller, select Security > AAA > RADIUS > Authentication to see a list of servers that have already been configured, as shown in Figure 15-2. If multiple servers are defined, the controller will try them in sequential order. Click New to create a new server.

Figure 15-2 Displaying the List of RADIUS Authentication Servers

Next, enter the server’s IP address, shared secret key, and port number, as shown in Figure 15-3. Because the controller already had two other RADIUS servers configured, the server at 192.168.200.30 will be index number 3. Be sure to set the server status to Enabled so that the controller can begin using it. At the bottom of the page, you can select the type of user that will be authenticated with the server. Check Network User to authenticate wireless clients or Management to authenticate wireless administrators that will access the controller’s management functions. ClickApply to complete the server configuration.

Figure 15-3 Configuring a New RADIUS Server

The process on a converged controller is similar, except that RADIUS servers are put into groups, then the group is applied as part of an authentication method list. The method list is used for authentication in any WLANs that are configured. Use the following steps to create a new RADIUS server.

Step 1. Select Configuration > Security.

Step 2. Under Security > AAA > Radius > Servers, click the New button to create a new RADIUS server entry. Enter the server’s name, IP address, and shared secret key string. Repeat this step to create any further RADIUS servers.

Step 3. Create a RADIUS server group by selecting Security > AAA > Server Groups > Radius. Move desired servers from the Available Servers list to the Assigned Servers list.

Step 4. Select Security > AAA > Method Lists > Authentication and define a new method that uses the RADIUS server. Move desired server groups from the Available Server Groups list to the Assigned Server Groups list.

Creating a Dynamic Interface

In Chapter 10, “Implementing Controller-based Deployments,” you learned about the different types of controller interfaces. A dynamic interface is used to connect the controller to a VLAN on the wired network. When you create a WLAN, you will bind the dynamic interface (and VLAN) to a wireless network.

To create a new dynamic interface on a centralized controller, navigate to Controller > Interfaces. You should see a list of all the controller interfaces that are currently configured. Click the New button to define a new interface. Enter a name for the interface and the VLAN number it will be bound to. In Figure 15-4, the interface named Engineering is mapped to wired VLAN 100. Click the Apply button.

Figure 15-4 Defining a Dynamic Interface Name and VLAN ID on a Centralized Controller

Next, enter the IP address, subnet mask, and gateway address for the interface. You should also define primary and secondary DHCP server addresses that the controller will use when it relays DHCP requests from clients that are bound to the interface. Figure 15-5 shows how interface Engineering has been configured with IP address 192.168.100.10. Click the Apply button to complete the interface configuration and return to the list of interfaces.

Figure 15-5 Editing the Dynamic Interface Parameters on a Centralized Controller

The process is similar on a converged controller. Create the interface by selecting Configuration > Controller > System > VLAN > Layer2 VLAN and entering a VLAN number and name as shown in Figure 15-6. In essence, you are creating a VLAN on the switch that is hosting the WLC.

Figure 15-6 Defining a VLAN on a Converged Controller

Next, the dynamic interface needs a way to bring Layer 3 connectivity to the Layer 2 VLAN. Select Configuration > System > VLAN > Layer3 Interface, then click New. Enter the interface description, IP addressing information, and a DHCP server address as shown in Figure 15-7.

Figure 15-7 Defining a Dynamic VLAN Interface on a Converged Controller

Creating a New WLAN

You can display a list of the currently defined WLANs by selecting WLANs from the top menu bar. In Figure 15-8, the controller has one WLAN called guest already defined. You can create a new WLAN by selecting Create New from the drop-down menu and then clicking the Go button.

Figure 15-8 Displaying a List of WLANs

You can display the same list of WLANs on a converged controller by selecting Configuration > Wireless > WLAN > WLANs. Click New to create a new WLAN or select an existing WLAN from the list to edit its parameters.

Next, enter a descriptive name as the profile name and the SSID text string. In Figure 15-9, the profile name and SSID are identical, just to keep things straightforward. The ID number is used as an index into the list of WLANs that are defined on the controller. The ID number becomes useful when you use templates in Prime Infrastructure (PI) to configure WLANs on multiple controllers at the same time.

Figure 15-9 Creating a New WLAN