Wireless LAN (WLAN)

Question 1

Omnidirectional Antennas

Answer 1

Also called whip antennas

Radiate outward in a donut-like pattern

Question 2

Yagi Antenna

Answer 2

A directional antenna that forms a 90 degree beam

Typical gain of 10 to 15 dbi

Question 3

Effective Isotropic Radiated Power (EIRP)

Answer 3

Measures power output

Calculated by taking the transmit power - the cable loss + the antenna gain.

40 dBm - 4 dB + 12 dBi =48 dBm

Question 4

Signal-to-Noise Ratio (SNR)

Answer 4

Difference between RSSI and the noise floor

Example:

Noise floor -85dBm - RSSI - 50dBm =35 dBm

Question 5

IEEE physical standards in order of earliest to latest

Answer 5

802. 11a 5 ghz band
803. 11b 2.4 ghz
804. 11g 2.4 ghz band, bandwidth of 20 MHz, max data rate 54 Mbps
805. 11n 2.4 ghz and 5 ghz bands, bandwidth of 20, 40 MHz, max data rate 600 Mbps
806. 11ac 5 ghz band, bandwidths 20,40,80,160, max data rate 3.464 GBPs
807. 11ax 2.4 ghz and 5 ghz bands, bandwidths of 20,40,80,160, max data rate 9.6 GBPs

Question 6

The 2.4 GHz Band

Answer 6

Divided into 14 channels each with a 20 MHz bandwidth

Question 7

The 5 GHz band

Answer 7

IEEE 802.11ac supports bandwidths of 20, 40, 80, 160 MHz

Question 8

Distributed Coordination Function (DCF)

Answer 8

Requires a station to wait for radio silence before transmitting

Question 9

Authentication Mechanisms

Answer 9

WebAuth- Open authentication that redirects to a captive portal

Shared key or Preshared key- Used with WPA personal mode encryption

802.1x- Uses EAP to integrate with authentication providers. Authentication servers can be Kerberos or Radius

Question 10

Location Services

Answer 10

Collects signal information from 3 or more APs and uses it to create a real-time map of WI-FI devices

Examples: Cisco DNA Spaces
Cisco Connected Mobile Experiences

Question 11

mW to dBm Relationship

Answer 11

1 mW= 0 dBm
10mW= 10 dBm
100mW= 20 dBm
1000mW = 30 dBm

1 watt = 1000mW

Question 12

Access Point Operation

Answer 12

Boot State
WLC Discovery State
CAPWAP Tunnel State
WLC Join State
Image Download State
Config Download State
Run State

Question 13

Phase Shift Key (PSK)

Answer 13

Modifys frequency of the carrier signal.

QPSK used as a fallback in environments with radio interference.

Question 14

Encryptions

WPA
WPA2 with CCMP
WPA3 with CCMP

Answer 14

WPA TKIP

WPA2 with CCMP uses the AES cipher

WPA2 Enterprise mode uses 802.1x and EAP

WPA3 with CCMP uses the AES cipher and CCMP. Also implements forward secrecy.

Question 15

802.2 Logical Link Control (LLC)

Answer 15

WLANs are divided into 2 sub layers: 802.11 MAC and 802.2 LLC.

Question 16

MIMO

Answer 16

Spatial Multiplexing: Takes data to be sent and splits it up. And simultaneously transmits using multiple radios.

Diversity: Similar to Spatial but one small difference. Sends same data simultaneously on different frequencies using antennas positioned differently.

Question 17

WLC Discovery Process

Answer 17

Up to 3 controllers

If AP has never connected to WLC it will broadcast a CAPWAP discovery request on UDP 5246

AP will try to resolves CISCO-CAPWAP-CONTROLLER. domain.local

Question 18

Auto-Anchor Mobility

Answer 18

Force clients to go through a particular WLC

Example: Guest tunneling

Question 19

The laws of 3s

Answer 19

States that a 3db difference indicates a twofold difference in the measured signal

Question 20

AP Modes

Answer 20

Local - Default
Monitor - IDS; rogue; location-based services
FlexConnect - AP can switch to VLAN operation
Sniffer
Rogue Detector
Bridge - can be used to mesh
Flex+Bridge
SE-connect - Cisco Spectrum Expert