Wireless Interview Questions & Answers – Network Professional Member Site

Ques1. What is Wi-Fi and what is WIMAX?

Wi-Fi is abbreviation for Wireless Fidelity. Wi-Fi is a wireless technology that uses radio waves to provide High speed network connectivity and communication across devices based on the IEEE 802.11 standards. Devices that can use Wi-Fi technology include PCs/Laptops, video-game consoles, phones and tablets, digital cameras, smart TVs, digital audio players and modern printers.

WiMAX is abbreviation for Worldwide Interoperability for Microwave Access. It is referenced by IEEE 802.16. WiMAX is also commonly termed 4G network.
WiMAX is used as wide area network for providing access between various wireless devices. WiMAX uses OFDM modulation scheme.

Ques2. What is 802.1x?

IEEE 802.1x is an IEEE standard for port-based network access control (PNAC).802.1X provides an authentication framework for wireless LANs, allowing a user to be authenticated by a central authority.). It is part of the IEEE 802.1 group of networking protocols. It provides an authentication mechanism to devices wishing to attach to a LAN or WLAN.

Ques3. Which encryption type does WPA2 uses?

WPA2 uses AES. AES is a newer Wi-Fi encryption solution used by the new and secure wpa2 standard. Tkip was the older encryption used in WPA.

Ques4. When 2 laptops wirelessly connected can communicate to each other directly, what type of topology has been created?

2 laptops wirelessly communicating to each other will be considered running on Full mesh topology (under ad-hoc Network) which means that each node of the network is connected directly to each of the other nodes.

Ques5. What is Piggybacking in context to Wi-Fi?

Piggybacking on internet access is the way of establishing a wireless connection by using another subscriber’s connection without the person’s permission or knowledge. Piggybacking is an unauthorized tapping into another’s connection with a public utility.
For e.g.- Piggybacking can be takes place like when an unauthorized person accessed the wireless connection of his neighbor Wi-Fi without his/her knowledge by using their static IP Address.
Ques6. What is the frequency range of 802.11a standard?

802.11a works on 5GHz frequency.
Ques7. What is the frequency range of 802.11g standard?

802.11g works on 2.5GHz frequency.
Ques8. What is data rate of 802.11a standard?

The IEEE 802.11a standard has a maximum data rate of up to 54Mbps
Ques9. What is data rate of 802.11g standard?

The IEEE 802.11g standard has a maximum data rate of up to 54Mbps.

Ques10. Why WPA encryption is preferred over WEP?

Below points enumerate the reason for preference of WPA over WEP –

a) WPA provides stronger encryption than WEP.
b) The access point and the client are manually configured with different WPA key values.
c) WEP Key values remain the same until the client configuration is changed.
d) WEP uses static encryption keys while the values of WPA keys can change dynamically

while the system is used.
e) WPA provides user authentication through EAP which is missing in WEP.

Ques11. What is IBSS and BSS?

IBSS is abbreviation for “Independent Basic Service Set”. IBSS allows 2 or more devices to communicate directly with each other without a need for a central device.

BSS is abbreviation for “Basic Service Set”. BSS wireless LAN is established using a central device called an Access Point that centralizes access and control over a group of wireless devices.

Ques12. What is ESS?

Extended Service Set (ESS) is created by connecting multiple Basic Service Set (BSS) via a distribution system. 2 or more Access Points are connected to the same Local Area Network to provide a larger coverage area which allows the client to move from one AP to another AP and still be the part of the LAN. This process is called roaming where client has leverage of physically changing locations and still be part of same WLAN. When a client senses that radio signal from the current AP are getting weaker, it finds a new AP with stronger signals starts using that AP. An ESS generally includes a common SSID to allow roaming from access point to access point without requiring client re-configuration.

Ques13. What is EAP?

In wireless communications (using EAP) , a user requests connection to a WLAN through an AP, which then requests the identity of the user and transmits that identity to an authentication server such as RADIUS. The server asks the AP for proof of identity, which the AP gets from the user and then sends back to the server to complete the authentication.EAP is defined by RFC 2284.

Ques14. What is Wi-Fi Hotspot?

A Wi-Fi hotspot is a physical location where people may obtain Internet access, via a wireless local area network (WLAN) using a router connected to an internet service provider. Public hotspots may be created by a business for use by customers, such as coffee shops or hotels, airports etc.

Ques15. What are the different modes of a Cisco Access Point (AP) operation?

 Local mode – This is the default mode of operation.
 REAP mode-REAP mode enables an LAP to reside across a WAN link and still be able to

communicate with the WLC and provide the functionality of a regular LAP.
 Monitor mode – act as dedicated sensors for location based services (LBS), rogue access

point detection, and intrusion detection (IDS).
 Rogue detector mode – LAPs that operate in Rogue Detector mode monitor the rogue

APs.

 Sniffer mode – An LWAPP that operates in Sniffer mode functions as a sniffer and captures and forwards all the packets on a particular channel to a remote machine that runs Airopeek.

Ques16. What is Fast roaming?

The concept of Fast roaming is that the device creates a handshake with another AP even before the client roams to the new AP. This allows the client to roam to another AP without re-authenticating.
In simple words, after a client connects to the first AP on the network, the client is “vouched for.” When a client device roams to a new AP, information from the original association is passed to the new AP to provide the client with credentials. The new AP therefore knows that this client has already been approved by the authentication server, and thus need not repeat the whole 802.1X/EAP exchange again.

Ques17. What are all the authentication mechanisms currently supported by Cisco Access Points (APs)?

This is a list of authentication mechanisms currently supported:

 WEP
 WPA- Personal and WPA2-Personal
 WPA-Enterprise and WPA2-Enterprise
 EAP authentication
 MAC authentication

Ques18. What is World Mode?

When world mode is enabled, the Cisco Access Point (AP) adds channel carrier set information to its beacon. Client devices with world mode enabled receive the carrier set information and adjust their settings automatically. For example, a client device used primarily in Japan can rely on world mode to adjust its channel and power settings automatically when that device travels to Italy and joins a network there. World mode is disabled by default.

Ques19. Which 2-3 devices can interfere with Wireless network operation since they work in same frequency?

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Ques20.

Microwave oven Cordless phone

What is Dynamic Transmit Power Control (DTPC) and how does it work?

By default, Cisco Aironet APs have dynamic transmit power control (DTPC) enabled. DTPC is automatic with Cisco WLCs but must be configured on autonomous APs. The objective of DTPC is to reduce the chance of one-way audio because of an imbalance of transmit power between the AP and the Wi-Fi radio of the client. DTPC accomplishes this by:

• Setting the phones transmit power to match the transmit power of the APs.

Ques21.

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Ques22.

What are three basic parameters to configure on a wireless access point?

SSID
RF
Channel authentication method

How do we prevent loops on the WLC?

• Having APs advertise their transmit power for the clients to learn.
With DTPC, Cisco access point transmits to Cisco CCX compliant client information about which power level to use. If client is CCX, the AP can tell to your client to adjust the power levels dynamically hence saving the battery life of the client. We can enable it in controller from the Main radio menu (Wireless > 802.11a > Network, in the General Field).

We can enable STP on the WLC to prevent loops. From the WLC GUI click Controller, then navigate to the advanced submenu located on the left side of the application. Click the Spanning Tree option, and choose Enable for Spanning Tree Algorithm located on the right side of the application.

By default, STP need not be enabled to prevent loops. Because each interface that is mapped to a WLAN on the WLC is mapped to primary and backup ports. Only one port is used at a particular point of time. Traffic from the WLAN is forwarded only through the primary port. WLC never uses the secondary port when the primary port is active. WLC uses the secondary port only when the primary port is down, so loops will not occur by default.

Ques23. What is the master controller mode on WLC?

Master controller mode comes into play when there are more than one controller the Access Point can connect to and it hasn’t been explicitly indicated which controller is primary or secondary. In such a scenario the “Master” controller setting is the tie breaker. When there is a master controller enabled, all newly added access points with no primary, secondary, or tertiary controllers assigned associate with the master controller on the same subnet. This allows the operator to verify the access point configuration and assign primary, secondary, and tertiary controllers to the access point

Ques24. What is the function of WLAN on WLC?

WLAN is similar to that of SSID in the access point. It is required for a client to associate with its wireless network.

Ques25. Is there any way to recover my password for WLC?

If we forget password in WLC version 5.1 and later, we can use the CLI from the serial console of the controller in order to configure a new user name and password.
After the controller boots up, enter the Restore-Password command at the user prompt. This command is only accepted for the initial user login and becomes disabled after a user logs in. We are prompted to enter a new username/password, which can then be used to log into the controller and modify settings.

Before version 5.1, there is no password recovery option on the Wireless LAN Controller (WLC). You need to set the WLC in order to factory defaults and reconfigure it. In order to set the WLC to factory defaults, power cycle the WLC, press the ESC Key during the boot up process from the console, and choose last option(5) in order to clear the configuration and reboot the Wireless LAN Controller.

Note: The new default username and password is admin. Ques26. What is FlexConnect in Cisco Wireless?

FlexConnect (previously known as Hybrid Remote Edge Access Point or H-REAP) is a wireless solution for branch office and remote office deployments. It enables you to configure and control access points in a branch or remote office from the corporate office through a wide area network (WAN) link without the deployment of a controller in each office. The FlexConnect access points (APs) can switch client data traffic locally and perform client authentication locally. When they are connected to the controller, they can also send traffic back to the controller.

Ques27. What is Difference between CAPWAP and LWAPP?

Below table enlists the difference between CAPWAP and LWAPP –

Ques28. Enlist 3 major differences between Cisco 2500 Series and 5500 Wireless Controllers?

3 main differences between Cisco 2500 and 5500 WLC are enlisted below –

Ques29. Kindly share models of some Outdoor Rugged Access Points/Bridges?

Below are some of the latest Cisco Outdoor Rugged Access Points –

 Aironet 1530 Series
 Aironet 1540 Series
 Aironet 1560 Series
 Aironet 1570 Series
 Aironet 1552 Access Point
 Industrial Wireless 3702

Ques30. Cisco 5520 Wireless Controller supports upto how many clients and APs?

Cisco 5520 WLC supports upto 1500 Access Points

Ques31.

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Though –

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Ques32. What is difference between Ad-Hoc and Infrastructure topology?

Below table provides detail of how both Topology differ from each other –

Ques33. What is difference between UWB and Wi-Fi?

Comparison between UWB (Ultra Wide-Band) and Wi-Fi (Wireless Fidelity) is shared in below table –

What are 3 main factors affecting Wireless Network?

Distance
Obstructions like wall and material Wireless standard in use

we have others factors also responsible for affecting the Wireless network as below

Signal Sharing – the more devices that communicate via access point, further the Wireless signal can degrade
Wireless Network Interference

What is difference between Ad-Hoc and Infrastructure topology?

Ques34. What is the difference between Wi-Fi and Bluetooth?

Ques35. What is the change in WLAN-11ac with respect to previous versions of WLAN?

There are 2 variants of 802.11ac – phase 1 and phase 2.
802.11ac is faster compared to previous standards because of the introduction of the below • Multi-User MIMO (MU-MIMO) – Clients get on and off the network quicker, allowing more clients to be served, Pre Wave 2 an access point would talk to the clients one at a time and this was called SU-MIMO. Multi-user MIMO is important because it allows access points and their many antennas to transmit (or talk) to multiple client devices all at the same time. This helps maximize air-time efficiency so that each client, regardless of what version of 802.11 it is running, gets the amount of airtime it’s supposed to get based on the technology supported.
• Wider RF Channels – Wave 2 improvement is the option to use 160-MHz channel widths. That’s double what we saw with Wave 1 technology. Think of this as a 2 line interstate road where two additional lines have been added. The top speeds depend on the whether the AP supports 80-MHz or 160-MHz channels, as well as whether the wireless client devices tapping your network support Wave 2.
• Four Spatial Streams – Wave 2 also supports four transmitting and receiving antennas while the previous iteration supported only three receive antennas. Just like we see in the image below, With 4 spatial streams an AP could send 4 streams of data to the same client at the same time. The client can then aggregate this 4 streams and thus improve its throughput. It is also important to notice that on the AP side, the greater the number of receive antennas, the greater the distance that a particular data rate can be sustained.