Troubleshooting Wireless Networks

Question 1

Bandwidth

Answer 1

Theoretical speed of data going across the network

Question 2

Throughput

Answer 2

Actual speed of data on the network

Question 3

Received Signal Strength Indication (RSSI)

Answer 3

Estimated measure of the power level that a radio frequency client
device is receiving from a wireless access point or wireless router

Question 4

o Effective Equivalent Isotropic Radiated Power (EIRP)

Answer 4

Maximum power radiated from an ideal isotropic antenna, given its
antenna gain, and the transmitter power of the radio frequency system

Question 5

Decibels over isotropic (dBi)

Answer 5

Tells signal strength being radiated from a wireless access point

Question 6

Wireless Considerations
o Vertical Antenna

Answer 6

▪ Radio frequency waves extend outward in all directions away from the
antenna and the wireless access point at an equal power level

Question 7

Dipole Antenna

Answer 7

Produces radio frequency waves extending outward in two directions

Question 8

Yagi Antenna

Answer 8

▪ A unidirectional antenna that sends the radio frequency waves in only
one direction

Question 9

Parabolic Grid Antenna

Answer 9

Allows the radio waves to be transmitted in only one direction over a
longer distance than a Yagi antenna
▪ Choose a parabolic or Yagi antenna for site-to-site connections
▪ For indoor use, you are more likely to use omnidirectional and
unidirectional antennas

Question 10

o Polarization

Answer 10

The orientation of the electric field (or transmission) from the antenna
▪ Most Wi-Fi networks use vertical polarization

Question 11

Channel Utilization

Answer 11

A statistic or measure of the amount of airtime utilization that occurs for
a particular frequency or channel
▪ Keep channel utilization under 30% to have a faster wireless network
▪ Access points and clients form a single broadcast domain when they
operate on the same channe

Question 12

Clear Channel Assessment (CCA)

Answer 12

Listens to see if another device is actively transmitting on the channel
before attempting to send frames on that channel
▪ High channel utilization leads to slower throughput for wireless networks

Question 13

Site Survey

Answer 13

Survey
▪ Process of planning and designing a wireless network to provide the
required wireless solution
● Configure devices to use less utilized channels
● Ensure proper coverage of the entire work areas
● Ensure wireless network is not being blocked or interfering with
physical obstacles within the building
▪ How does a site survey work?
1. Wireless client sends a probe request to discover any 802.11
wireless networks in proximity to itself
2. Receiving access point checks to see if it can support the data rate
the client requested
3. Wireless client sends a low-level 802.11 authentication frame to
the access point to begin authentication
4. Access point receives authentication frame and responds with an
acknowledgement to continue the handshake
5. Wireless client chooses the access point it wants to associate with
and sends an association request
6. Access point processes the association request if the information
sent matches its capabilities
7. Client is fully connected and associated and can now conduct any
data transfer it needs and use the wireless network
▪ Basics steps
● Scan airwaves
● Find access points
● Request association
● Authenticate
● Contact DHCP server
▪ Clients should be located in high signal strength areas to speed up the
association process

Question 14

Coverage and Interference
o Coverage

Answer 14

A measure of how much area around a wireless transmitter is there
sufficient signal strength for wireless devices to utilize
● Client
● RSSI (decibel)
● Access Point
▪ EIRP (dBi)
▪ Signal booster
▪ Larger antenna
▪ Wireless repeater
▪ Second access point

Question 15

Interference

Answer 15

Occurs when multiple wireless networks communicate on the same
channel using the same frequency
▪ Use channels 1, 6, and 11 in the 2.4 GHz spectrum
▪ Ensure a 10-15% overlap between access points for sufficient coverage

Question 16

Attenuation

Answer 16

Reduction of signal strength between the transmission and receipt of the
signal

Question 17

Multipath Reception

Answer 17

Occurs when the transmitted signal bounces off walls and other physical
objects and then is redirected to the receiver
● Client Disassociation
o Idle Timeout
▪ Occurs when there’s no traffic within 300 seconds
▪ Send a keep alive packet every few minutes to
remain connected
o Session timeout
▪ Occurs when there’s no traffic within 1800 seconds
o Wireless network change
▪ Occurs whenever the wireless local area network is
changed
o Manual deletion
▪ Occurs whenever a client is removed by an
administrator
o Authentication timeout
▪ Occurs when the authentication or key exchange
process fails to finish in time
o Access point radio reset
▪ Occurs when a change is made to the wireless
network

Question 18

Deauthentication Attack

Answer 18

A common wireless attack used by hackers to disassociate wireless clients
and make them attempt to reconnect to the access point

Question 19

Incorrect Configurations

Answer 19

Wrong SSID
▪ Service Set Identifier (SSID) is a natural language name used to identify a
wireless network in an 802.11 network
o Incorrect passphrase
▪ Passphrase/ Pre-Shared Key is used to encrypt and decrypt data sent and
received by a wireless network
o Encryption mismatch
▪ Occurs when the client and the access point are using different
encryption types
● WEP – RC4
● WPA – TKIP
● WPA2 – AES
▪ To fix this, attempt to reinstall the drivers for your wireless adapter
● Change protocol type
● Disable antivirus tools
● Reinstall drivers

Question 20

Captive Portal Issues

Answer 20

o Captive Portal
▪ A web page displayed to newly-connected Wi-Fi users before being
granted broader access to network resources
o HTTP Redirect
▪ Redirects all traffic to a web server which then redirects them to a
captive portal using a 302 HTTP status code
o ICMP Redirect
▪ Sends error messages and operational information indicating the success
or failure of communicating with another IP address
o DNS Redirect
▪ The client is redirected by the onboard DNS server to the captive portal
webpage
● Open a web browser and try to go to any website, such as
Google.com or Facebook.com