Chapter 18: Quiz - Wireless Architecture Infrastructure (Answers) CCNPv8 ENCOR

13. What are the two locations that a WLC is commonly placed in when deploying a centralized wireless LAN topology? (Choose two.)

implemented near the network core
implemented within the data center
implemented within the access layer
implemented as software on an AP
embedded within an access switch

Explanation: A WLC deployed in a centralized or unified wireless LAN topology is commonly placed in a central location such as a data center or near the network core. A centralized WLC design facilitates the enforcement of wireless security policies.

14. How often are keepalives sent from an AP to a controller over a wired network?

every 3 seconds
every 6 seconds
every 10 seconds
every 30 seconds

Explanation: By default, an AP will send a keepalive message every 30 seconds over a wired network to the WLC that it joined.

15. When considering the performance of a wireless antenna, what is a radiation pattern?

a graph of the RF signal as a frequency compared to time
a plot that shows the dynamic rate shifting of a wireless connection over varying distance
a graph comparing the varying wireless antenna types and the measured distances achievable
a plot that shows the relative signal strength around an antenna

Explanation: Antenna pattern plots can be a bit confusing to interpret as they are placed on a 2D paper environment. However, it is important to review the radiation patterns, which are viewed as a plot that shows the relative signal strength of an antenna drawn out in a three-dimensional form on a two-dimensional medium.

16. Which statement describes an autonomous access point?

It is used for networks that require a large number of access points.
It is a standalone access point.
It is server-dependent.
It is managed by a WLAN controller.

Explanation: An autonomous access point is used in environments that require a small number of access points. As network demands increase, more access points can be added to the environment with each access point acting independently of another. An autonomous access point can be configured using either a GUI or CLI.

17. When must both the ip forward-protocol and ip helper-address commands be entered on a Cisco device during a WLC deployment in order to successfully forward CAPWAP Discovery Requests?

when a router is positioned between the WLC and the lightweight AP
when an access switch is positioned between the WLC and the lightweight AP
when a WLC is deployed within a centralized WLAN network topology
when a WLC is deployed using an embedded access switch

Explanation: A Cisco router separates broadcast domains and will prevent broadcasted CAPWAP Discovery Requests from being forwarded between a WLC and an access point. The ip forward-protocol and ip helper-address commands must be entered on the Cisco router to enable the forwarding of broadcast traffic to the specified WLC.

18. What is the function provided by CAPWAP protocol in a corporate wireless network?

CAPWAP provides the encapsulation and forwarding of wireless user traffic between an access point and a wireless LAN controller.
CAPWAP provides the encryption of wireless user traffic between an access point and a wireless client.
CAPWAP provides connectivity between an access point using IPv6 addressing and a wireless client using IPv4 addressing.
CAPWAP creates a tunnel on Transmission Control Protocol (TCP) ports in order to allow a WLC to configure an autonomous access point

Explanation: CAPWAP is an IEEE standard protocol that enables a WLC to manage multiple APs and WLANs. CAPWAP is also responsible for the encapsulation and forwarding of WLAN client traffic between an AP and a WLC.

19. Which DHCP feature or option provides a list of suggested wireless controllers to a lightweight AP?

DHCP option 150
DHCP option 43
DNS server IPs
default router IP

Explanation: A local DHCP server can provide an access point with an IP address and with DHCP option 43, which is a list of suggested WLC IP addresses.

20. What is the maximum recommended round-trip time between an access point and a controller when trying to maintain near real-time wireless communication?

less than 50 ms
less than 75 ms
less than 100 ms
less than 150 ms

Explanation: The round-trip time (RTT) between an AP and a controller should be less than 100 ms so that wireless communication can be maintained in near real-time.

21. What is the default mode being used by a lightweight access point?

sniffer
local
monitor
bridge

Explanation: The default lightweight mode is local and provides one or more functioning BSSs on a specific channel.

22. Which step can be taken to minimize downtime when moving APs from one controller to a new controller with a different code release?

Predownload the new release to the APs to be moved.
Configure the APs to be moved with the IP address of the new controller.
Connect the new WLC as the primary controller and force the APs to join the new controller and automatically download the software release.
Reboot the new controller with the software release and then join the current APs to it.

Explanation: In order to best minimize downtime, it is recommended to download a new code release to a controller and delay any reboots. Next, the new release can be predownloaded to the APs. Both the controller and the APs can reboot during a maintenance window and load the new image.

23. What is a characteristic of a Yagi antenna that is used by Cisco Aironet Access Points?

It provides 360-degree coverage.
It can be used for long-distance Wi-Fi networking.
It is also referred to as a “rubber duck” design.
It has the same characteristics as an omnidirectional Wi-Fi antenna.

Explanation: Yagi antennas are a type of directional radio antenna that can be used for long-distance Wi-Fi networking. They are typically used to extend the range of outdoor hotspots in a specific direction, owing to their high gain. Omnidirectional Wi-Fi antennas are also referred as a “rubber duck” design and provide 360-degree coverage.

24. What is a difference between autonomous APs and controller-based APs in wireless LANs?

Controller-based APs support PAgP and LACP protocols, whereas autonomous APs do not.
When wireless demands increase, controller-based APs provide a better solution than do autonomous APs.
Autonomous APs are easier to configure and manage than are controller-based APs.
Autonomous APs require no initial configuration, whereas the lightweight APs require an initial configuration before communicating with a WLAN controller.

Explanation: When the wireless demands increase, more autonomous APs would be required. Each of them operates independently of the others and each one requires manual configuration and management. This would become overwhelming if many APs are needed. Controller-based APs require no initial configuration and are often called lightweight APs. Controller-based APs are useful in situations where many APs are required in the network. As more APs are added, each AP is automatically configured and managed by the WLC. The WLC does not support PaGP or LACP.

“Do I Know This Already?” Quiz Answers:

1. Suppose that a lightweight AP in default local mode is used to support wireless clients. Which one of the following paths would traffic usually take when passing from one wireless client to another?

Through the AP only
Through the AP and its controller
Through the controller only
None of these answers (Traffic must go directly over the air.)

Explanation: An AP transports client traffic through a tunnel back to a wireless LAN controller. Therefore, client-to-client traffic typically passes through both the AP, the controller, and back through the AP.

2. A centralized wireless network is built with 1 WLC and 32 lightweight APs. Which one of the following best describes the resulting architecture?

A direct Layer 2 path from the WLC to each of the 32 APs, all using the same IP subnet
A direct Layer 3 path from the WLC to each of the 32 APs, all using the same IP subnet
32 CAPWAP tunnels daisy-chained between the APs, one CAPWAP tunnel to the WLC
32 CAPWAP tunnels—1 tunnel from the WLC to each AP, with no IP subnet restrictions

Explanation: Because the network is built with a WLC and APs, CAPWAP tunnels are required. One CAPWAP tunnel connects each AP to the WLC, for a total of 32 tunnels. CAPWAP encapsulates wireless traffic inside an additional IP header, so the tunnel packets are routable across a Layer 3 network. That means the APs and WLC can reside on any IP subnet as long as the subnets are reachable. There are no restrictions for the APs and WLC to live on the same Layer 2 VLAN or Layer 3 IP subnet.

3. Which of the following unique features is true in an embedded wireless network architecture?

An access layer switch can also function as an AP.
All WLCs are converged into one device.
Large groups of APs connect to a single access layer switch.
An access layer switch can also function as a WLC.

Explanation: In an embedded design, an access layer switch also functions as a WLC so that all user access (wired and wireless) converges in a single layer.

4. Which one of the following comes first in a lightweight AP’s state machine after it boots?

Building a CAPWAP tunnel
Discovering WLCs
Downloading a configuration
Joining a WLC

Explanation: An AP discovers all possible WLCs before attempting to build a CAPWAP tunnel or join a controller.

5. If a lightweight AP needs to download a new software image, how does it get the image?

From a TFTP server
From an FTP server
From a WLC
You must preconfigure it.

Explanation: After an AP boots, it compares its own software image to that of the controller it has joined. If the images differ, the AP downloads a new image from the controller.

6. Which of the following is not a valid way that an AP can learn of WLCs that it might join?

Primed entries
List from a previously joined controller
DHCP
Subnet broadcast
DNS
Over-the-air neighbor message from another AP

Explanation: An AP can learn controller addresses by using any of the listed methods except for an over-the-air neighbor message. APs do send neighbor messages over the air, but they are used to discover neighboring APs—not potential WLCs to join.

7. If an AP tries every available method to discover a controller but fails to do so, what happens next?

It broadcasts on every possible subnet.
It tries to contact the default controller at 10.0.0.1.
It reboots or starts discovering again.
It uses IP redirect on the local router.

Explanation: If an AP cannot find a viable controller, it reboots and tries the discovery process over again.

8. Which of the following is the most deterministic strategy you can use to push a specific AP to join a specific controller?

Let the AP select the least-loaded controller
Use DHCP option 43
Specify the master controller
Specify the primary controller

Explanation: If the primary controller responds to an AP’s discovery methods, the AP will always try to join it first, ahead of any other controller. Configuring an AP with a primary controller is the most specific method because it points the AP to a predetermined controller. Other methods are possible, but they can yield ambiguous results that could send an AP to one of several possible controllers.

9. Which of the following antennas would probably have the greatest gain?

Patch
Dish
Yagi
Dipole
Integrated

Explanation: A parabolic dish antenna has the greatest gain because it focuses the RF energy into a tight beam.

10. An omnidirectional antenna usually has which of the following characteristics? (Choose two.)

Low gain
Small beamwidth
High gain
Zero gain
Large beamwidth

Explanation: An omnidirectional antenna is usually used to cover a large area. Therefore, it has a large beamwidth. Because it covers a large area, its gain is usually small.