Configuring Wireless networks

Question 1

What does 802.11 use to cope with contention?

Answer 1

CSMA/CA (carrier sense multiple access with collision avoidance).
Under CSMA/CA when a station receives a frame, it performs error checking. If the frame is intact, the station responds with an acknowledgment (ACK). If the ACK is not received, the transmitting station resends the frame until timing out.

A station broadcasts a request to send (RTS) with the source and destination and the time required to transmit. The receiving station responds with a clear to send (CTS), and all other stations in range do not attempt to transmit within that period.

Question 2

What speed did the original 802.11 work at?

Answer 2

1 Mbps

Question 3

What is a frequency band?

Answer 3

Portion of the microwave radio-frequency spectrum in which wireless products operate, such as 2.4 GHz band or 5 GHz band. Also called frequencies.
Support for a given Wi-Fi standard determines which bands are available.

Within each band, the radio is configured to use a specific range of frequencies, referred to as a channel.

Question 4

What is a channel?

Answer 4

Subdivision of frequency bands used by Wi-Fi products into smaller channels to allow multiple networks to operate at the same location without interfering with one another.

Question 5

How many non overlapping sub channels does the 5GHz have?

Answer 5

The 5 GHz band is subdivided into 24-25 (dependent upon region).
Each of which is 20 MHz wide.

Question 6

What is DFS?

Answer 6

Dynamic Frequency selection
A 802.11h standard.
Specifies a method to scan for radar signals and prevent an access point from using channels that would cause interference.

Question 7

What does standard 802.11a do?

Answer 7

Uses 5 GHz frequency band
Has a nominal rate of 54Mbps
Has a multiplexed carrier scheme called Orthogonal Frequency Division Multiplexing (OFDM).

Question 8

What does standard 802.11b do?

Answer 8

Uses the 2.4 GHz frequency band
Nominal rates of 11 Mbps
Standardized the use of carrier method Direct Sequence Spread Spectrum (DSSS) and Complementary Code Keying (CCK) signal encoding.

Question 9

What are the non overlapping channels in 2.4 GHz?

Answer 9

1, 6, and 11.

Question 10

What does the 802.11g standard do?

Answer 10

Uses 2.4 GHz frequency band
Nominal rates of 54 Mbps.
Also uses OFDM.
Has backwards support for 802.11b clients.
When in 802.11b compatibility mode, it drops back to using DSSS.

Question 11

What does the 802.11n standard do?

Answer 11

AKA Wi-Fi 4
Uses both 2.4 and 5 GHz bands
Uses MIMO multiple input multiple output.
Allows two adjacent 20 MHz channels to be combined into a single 40 MHz channel (channel bonding).
nominal speed per stream 72 Mbps.
Uses high throughput (HT)/greenfield mode for maximum performance or HT mixed mode for compatibility with older standards

Question 12

What does 802.11ac standard do?

Answer 12

AKA Wi-Fi 5
Uses only 5GHz band.
Its goal is to get throughput like that of Gigabit Ethernet or better.

Question 13

What does 802.11ax do?

Answer 13

AKA Wi-Fi 6
Also uses 6 GHz frequency band.
Uses OFDM with multiple access OFDMA
It provides better support for IoT devices.
Allows an access point to support legacy Wi-Fi 4/5 stations efficiently.

Question 14

What is Multiuser MIMO (MU-MIMO)?

Answer 14

Use of spatial multiplexing to allow a wireless access point to support multiple client stations simultaneously.

Allows the AP to use its multiple antennae to process a spatial stream of signals in one direction separately from other streams.
Meaning that groups of stations on a different alignment can connect simultaneously and also obtain more bandwidth.

Wi-Fi 6 supports up to eight stations in parallel, while Wi-Fi 5 supports up to four.

Question 15

What is Band Steering?

Answer 15

Feature of Wi-Fi that allows an access point to try to ensure that clients use a particular frequency band, such as 5 GHz rather than 2.4 GHz.

Question 16

What is the distance between cell or base stations?

Answer 16

5 miles/ 8km

Question 17

Tell me about 4G LTE.

Answer 17

Max downlink of 150 Mbps but around 20 Mbps real world performance.

LTE-A(Advanced)- Has a 300 Mbps downlink but around 90 Mbps real world performance.

Question 18

Tell me about 5G.

Answer 18

Rather than a single large antenna serving a large wireless cell, 5G involves installing hundreds of smaller antennae to form an array that can take advantage of multipath and beamforming to overcome the propagation limitations of the spectrum. This is also referred to as massive MIMO.

In theory has a max peak rate of 20 Gbps but real world speeds are about 50-300 Mbps

Question 19

What are Geostationary Orbital Satellite Internet.

Answer 19

When satellites were placed in high geostationary orbit (Historically).
The transfer rates available vary between providers and access packages, but 2 or 6 Mbps up and 30 Mbps down would be typical.

Question 20

What is Low Earth Orbital Satellite Internet Access?

Answer 20

A different type of service uses an array of satellites positioned in low Earth orbit (LEO).
It supports better bandwidth (around 70–100 Mbps at the time of writing).
The drawback is that the satellites move relative to the surface of Earth. The customer’s premises antenna must be provisioned with a motor so that it can periodically realign with the array.

Question 21

How long can a SSID be ?

Answer 21

Up to 32 bytes in length and for maximum compatibility should only use ASCII letters and digits plus the hyphen and underscore characters.

Question 22

What is a infrastructure topology?

Answer 22

Means that each station is configured to connect to the WLAN via an access point (AP). This makes a logical star topology.

Question 23

What is the BSSID?

Answer 23

Basic Service Set Identifier
The MAC address of an access point supporting a basic service area. (identifies the access point hosting a BSS.)

Question 24

What is a BSS?

Answer 24

The foundational building block of an IEEE 802.11 network.
Consists of a single access point (AP) connected to a wired network, which manages communication for one or more wireless client devices.

Question 25

What is the cabled network referred to as?

Answer 25

As a distribution system (DS).

Question 26

What is a ESS?

Answer 26

Extended Service Set. Can be formed by multiple APs connected to the same distribution system. An ESS is a group of basic service sets that are all configured with the same SSID and security information. An ESSID has the same format as an SSID.

Question 27

What should a device supporting the Wi-Fi standards indoor range be?

Answer 27

30 meters (100ft) Outdoor range can be double or triple indoor range.

Question 28

What is DRS?

Answer 28

Dynamic Rate Switching/Selection (DRS). A mechanism to determine an appropriate data rate based on the signal quality. ex. If the signal is strong, the station will select the highest available data rate, if the signal is weak, the station will reduce the data rate.

Question 29

What is RSSI?

Answer 29

Received Signal Strength Indicator. The strength of the signal from the transmitter as measured at the client end. When measuring RSSI, dBm will be a negative value with values closer to zero representing better performance -30 dBm is considered to be a perfect signal. A value around -65 dBm represents a good signal, while anything worse than -80 dBm is likely to suffer packet loss or be dropped. The RSSI must exceed the minimum receiver sensitivity.

Question 30

What is a wireless survey?

Answer 30

Documentation about a location for the purposes of building an ideal wireless infrastructure; it often contains optimum locations for wireless antenna and access point placement to provide the required coverage for clients and identify sources of interference. It is a critical planning tool to ensure that the WLAN delivers acceptable data rates to the supported number of devices in all the physical locations expected.

Question 31

What is a BSA?

Answer 31

Basic Service Area. The area served by a single AP.

Question 32

What is a ESA?

Answer 32

Extended Service Area. The area where stations can roam between access points to stay connected to the same ESSID

Question 33

What is a DS?

Answer 33

Distribution system. Connecting access points to a switched network via cabling to facilitate roaming within an extended service area (ESA). A wireless distribution system uses a access points configured in repeater mode to facilitate roaming.

Question 34

What is a WDC?

Answer 34

Wireless distribution center. When access points are configured to create wireless-only networks in areas where it is not possible to run cabling.

Question 35

What is a Wireless controller and what does it do?

Answer 35

A hardware device that allows for centralized management and monitoring of APs on the network. low for centralized management and monitoring of the APs on the network. Device that provides wireless LAN management for multiple APs. Can also aggregate client traffic and provide a central switching and routing point between the WLAN and wired LAN

Question 36

What's a AP that's firmware lets it handle clients without the use of a wireless controller?

Answer 36

An autonomous AP. Access point whose firmware contains enough processing logic to be able to function autonomously and handle clients without the use of a wireless controller

Question 37

What's a AP that requires a wireless controller to function called?

Answer 37

A lightweight AP. Access point that requires a wireless controller in order to function.

Question 38

What is LWAPP?

Answer 38

Lightweight Access Point Protocol. Allows an AP configured to work in lightweight mode to download an appropriate SSID, standards mode, channel, and security configuration Cisco wireless controllers normally communicate this way.

Question 39

What is CAPWAP?

Answer 39

Control And Provisioning of Wireless Access Points. An alternative to LDWAPP.

Question 40

What are most wireless radios fitted with?

Answer 40

An omnidirectional vertical rod-type antennae. An omnidirectional antenna receives and sends signals in all directions more or less equally. APs with omnidirectional antennae should ideally be ceiling mounted for best coverage.

Question 40

What is a unidirectional antenna used for?

Answer 40

To extend the signal to a particular area, you can use a unidirectional antenna focused in a single direction. Both the sender and receiver must use directional antennae, or one will be able to receive signals but not send responses Useful for point to point wireless bridge connections.

Question 41

What is polarization?

Answer 41

Orientation of the wave propagating from an antenna. ex. When the rod is pointed up relative to the floor, the wave is vertically polarized; if you orient the rod parallel to the floor, the wave is horizontally polarized. To maximize signal strength, the transmission and reception antennae should normally use the same polarization. NOTE: Some antennae are dual-polarized, meaning that they can be installed in either orientation. Dual-polarized antennae are also the best way to support mobile devices, as these can be held by their user in a variety of orientations.

Question 41

Name some unidirectional antennae.

Answer 41

Yagi (a bar with fins) and parabolic (dish or grid) form factors.

Question 42

What is a ad hoc topology?

Answer 42

The wireless adapter allows connections to and from other devices. This is referred to as an Independent Basic Service Set (IBSS). This topology does not require an access point. All the stations within an ad hoc network must be within range of one another. An ad hoc network might suit a small workgroup of devices.

Question 43

What is a Wireless mesh network? (WMN)

Answer 43

The nodes in a WMN are capable of discovering one another and peering, forming a Mesh Basic Service Set (MBSS). The mesh stations can perform path discovery and forwarding between peers using a routing protocol, such as the Hybrid Wireless Mesh Protocol (HWMP). More scalable than ad hoc Mesh topologies are becoming increasingly popular and are the foundation of most internet of things (IoT) networks.

Question 44

What is a wireless point to point normally used for?

Answer 44

As a means of bridging two locations when it is not possible to connect them using cables.

Question 45

What does the beamwidth of an antenna indicate?

Answer 45

The amount of directionality.

Question 46

What is the role of Wi-Fi Direct in wireless networking?

Answer 46

Wi-Fi Direct allows devices, such as printers, to act as a limited access point, enabling other devices to connect directly for specific tasks like sending print jobs wirelessly. This feature is particularly useful for peer-to-peer connections and is an alternative to the traditional ad hoc network setup.

Question 47

Tell me about WPA and how it differs from WEP.

Answer 47

Like WEP, version 1 of WPA uses the RC4 stream cipher to encrypt traffic but adds a mechanism called the Temporal Key Integrity Protocol (TKIP) to try to mitigate the various attacks against WEP that had been developed.

Question 48

Tell me about WPA2.

Answer 48

Uses a 4 way handshake. Uses the Advanced Encryption Standard (AES) cipher deployed within the Counter Mode with Cipher Block Chaining Message Authentication Code Protocol (CCMP). AES replaces RC4, and CCMP replaces TKIP from WPA.

Question 49

Tell me about WPA3

Answer 49

Uses Simultaneous Authentication of Equals (SAE) which replaces WPA2 4 way handshake. Replaces AES CCMP with AES Galios Counter Mode Protocol (GCMP) Mandates use of encryption for management frames. Encrypts open Wi-Fi network.

Question 50

What are the 3 types of Wi-Fi authentications?

Answer 50

personal: uses SAE and PSK open: enterprise: uses 802.11X to use EAP and AAA authentication servers (RADIUS or TACACS+)

Question 51

What does a captive portal do?

Answer 51

Web page or website to which a client is redirected before being granted full network access. The portal may also be designed to enforce terms and conditions and/or take payment to access the Wi-Fi service. Can be combined with open authentication.

Question 52

What are some BYOD issues?

Answer 52

Compatibility/support, and Security

Question 53

What are Deauthentication attacks?

Answer 53

Sends a stream of spoofed management frames to cause a client to deauthenticate from an AP. This might allow the attacker to interpose the evil twin, sniff information about the authentication process, or perform a denial of service (DoS) attack against the wireless infrastructure. Can be coupled with a evil twin attack PROTECTION: can be mitigated if the wireless infrastructure supports Management Frame Protection (MFP/802.11w). Both the AP and clients must be configured to support MFP.

Question 54

What is a solution to evil twin and rouge attacks?

Answer 54

A solution to the risk of rogue access points is to use EAP-TLS security so that the authentication server and clients perform mutual authentication.

Question 55

What is the nominal bit rate determined by?

Answer 55

Standards support (Wi-Fi 5 or Wi-Fi 6, for instance), use of bonded channels, and optimizations, such as MU-MIMO.

Question 56

What is RF attenuation?

Answer 56

Loss of signal strength due to distance and environmental factors. Also referred to as free space path loss.

Question 57

How can signal strength and noise be measured?

Answer 57

With a Wi-Fi analyzer. This is a device or software that can report characteristics of a WLAN, such as signal strength and channel utilization.

Question 58

What is antenna cable attenuation?

Answer 58

Signal loss caused by an external antenna connected to an access point over cabling.

Question 59

What is EIRP?

Answer 59

Effective Isotropic Radiated Power Signal strength from a transmitter, measured as the sum of transmit power, antenna cable/connector loss, and antenna gain. calculated as the sum of transmit power, antenna cable/connector loss, and antenna gain.

Question 60

What are the 2 main types of channel interference?

Answer 60

Co-channel interference (CCI): Where access points within range of one another are configured to use the same channel. CCI can be measured as a channel utilization percentage. Channel utilization can be measured from the access point or by using a Wi-Fi analyzer. As a design goal, a channel should exhibit no more than 50% utilization. Adjacent channel interference (ACI): Occurs when access points are configured to use different but overlapping channels, such as 1 and 3 in the 2.4 GHz band. ACI slows down the CSMA/CA process and raises noise levels.

Question 61

How much MHz spacing should be allowed so channel overlap can be avoided?

Answer 61

At least 25MHz.

Question 62

What are some sources other than CCI and ACI that cause interference for wireless connections.

Answer 62

Reflection/bounce (multipath interference): Mirrors or shiny surfaces cause signals to reflect, meaning that a variable delay is introduced. Refractions Glass or water can cause radio waves to bend and take a different path to the receiver. Absorption: Refers to the degree to which walls, windows, and people will reduce signal strength. EMI: which can be detected using a spectrum analyzer.

Question 63

What is the recommended AP power setting relative to the weakest client power?

Answer 63

Setting the AP's transmit power to 2/3rds of the weakest client's power helps balance the communication capabilities between the AP and client devices. This ensures that both the AP and the clients can effectively send and receive signals, reducing the likelihood of one-way communication issues and maintaining a stable connection.

Question 64

What is the inverse-square rule in the context of wireless signals?

Answer 64

Doubling the distance between devices reduces the signal strength by a factor of four.

Question 65

What another name for APs?

Answer 65

cells