Wireless Network Troubleshooting and Performance Optimization - Make Questions

Troubleshooting Wireless Issues
Objective 5.4: Given a scenario, troubleshoot common performance issues
● Introduction
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CompTIA Network+
(N10-009) (Study Notes)
○ RSSI (Received Signal Strength Indicator)
■ Estimated measure of the power level that a radio frequency client device
is receiving from a wireless access point or wireless router
● Over -90 dB - Extremely weak
● Around -65 dB - Fairly strong
● -55 dB - Strong
● -30 dB - Extremely strong
○ EIRP (Effective Isotropic Radiated Power)
■ The maximum amount of power that could be radiated from an ideal
isotropic antenna, given its antenna gain, and the transmitted power of
the radio frequency system
● Wireless Coverage Issues
○ Coverage (Wireless Networks)
■ Measure of the area around a wireless transmitter with sufficient signal
strength for device use
■ Conducted via wireless site surveys to create a heat map showing signal
strength levels (green to red)
○ Signal Measurement
■ Client Side
● Received Signal Strength Indicator (RSSI) – decibels
■ Access Point Side
● Effective Isotropic Radiated Power (EIRP) – dBi
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○ Common Coverage Issues
■ Insufficient coverage in multi-story buildings
● Signal degradation with distance and obstacles like ceilings
● RSSI decreases when the signal has to penetrate through the floor
○ Improving Coverage
■ Use signal boosters
■ Antennas with higher dBi ratings
● Two factors affecting single wireless access point
○ Amount of power the transmitter is sending out
○ Size of antenna
○ Example
■ Replacing a 5 dBi antenna with a 9 dBi antenna can
double range under ideal conditions
■ Wireless Repeaters
● Layer one devices with two radios that receive and retransmit
signals at full strength, extending coverage area
● Useful in multi-story buildings, with repeaters placed strategically
to boost signals from lower floors to upper floors
■ Additional access points in Extended Service Set (ESS) configuration
● Extended Service Set (ESS)
○ Combining multiple access points into a single network
with seamless roaming for devices
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○ Example
■ Using two access points on different floors of a
house connected by Ethernet cables for complete
coverage
■ Wireless Mesh Systems
● Combination of repeaters and access points into a single device to
create a mesh network
● Ideal for larger homes and offices, eliminating the need for
Ethernet cables to each device
● Interference Issues
○ Interference in Wireless Networks
■ Interference
● Occurs when multiple wireless networks communicate on the
same channel at the same frequency
■ Overlapping channels (e.g., channel 4 and channel 6) can lead to
interference and network slowdowns
■ Conduct a site survey to identify channels and frequencies in use and plan
access point locations accordingly
○ Channel Planning in 2.4 GHz Networks
■ Use channels 1, 6, and 11 to avoid overlap
■ For extended service set networks
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CompTIA Network+
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● Plan access point locations and channel assignments carefully to
minimize interference
■ Maintain a 10-15% overlap between access points for sufficient coverage
and seamless device handoff
○ Channel Planning in 5 GHz Networks
■ Utilize a honeycomb pattern for access point installation
■ Ensure no channel repetition until at least two zones away to minimize
interference and ensure coverage
○ Attenuation in Wireless Networks
■ Attenuation
● Reduction of signal strength between transmission and reception
● Can occur within antenna cables or in the radio frequency wave as
it travels
■ Causes of Attenuation
● Distance
● Physical obstacles (e.g., walls)
● Signal interference
■ Reducing Attenuation
● Use higher quality, lower resistant components for antennas and
cables to reduce attenuation
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CompTIA Network+
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■ Radio Frequency Wave Signal Attenuation
● Multipath Reception
○ Occurs when signals bounce off objects
○ Can cause attenuation and weaker signals
○ Signals may reach the receiver but with lower signal
strength, leading to lower throughput
● Client Disassociation Issues
○ Disassociation Issues in Wireless Networks
■ Reasons for client disassociation
● Idle Timeout
○ Occurs after 300 seconds (5 minutes) of inactivity
■ Default setting on most access points
○ Some clients send keep-alive packets
● Session Timeout
○ Occurs after 1800 seconds (30 minutes)
○ Client should re-authenticate and re-establish connection
automatically
● Wireless Network Change
○ Disables and re-enables the network
○ Requires devices to reconnect and re-authenticate
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CompTIA Network+
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● Manual Deletion
○ Occurs when an administrator removes a client
● Authentication Timeout
○ Occur when authentication/key exchange process fails to
finish in time
○ Client needs to restart authentication process
● Access Point Radio Reset
○ Occurs when a change is made to the wireless network
○ Deauthentication Attack
■ Used by hackers to disassociate clients
■ Attacker captures packets used in association/authentication processes to
crack shared passphrase
■ Continual deauthentication should be investigated for possible attacks.
○ Understanding these disassociation issues is crucial for network administrators to
differentiate between normal disassociations and potential attacks, allowing for
appropriate responses and network security
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CompTIA Network+
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● Incorrect Wireless Configurations
○ Incorrect Configurations in Wireless Networks
■ Wrong SSID
● Service Set Identifiers (SSIDs)
○ Natural language names used to identify wireless networks
in 802.11 protocol
○ Examples
■ "Starbucks Wi-Fi"
● Incorrect SSID not usually an issue due to dropdown menu
selection
● Manually entering SSID may lead to mistyping errors
● Evil Twin SSID
○ Similar SSID in the same area may indicate an evil twin
○ Connecting to wrong SSID can lead to malware infection or
on-path attack
■ Incorrect Passphrase
● Passphrase/Pre-shared Key
○ Required for authentication to wireless networks
○ Used to encrypt and decrypt data
● Entering wrong passphrase leads to disassociation from access
point
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CompTIA Network+
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● Troubleshooting Incorrect Passphrase
○ Reinstall wireless network adapter drivers if passphrase is
correct but access point reports it as incorrect
● Corruption in drivers may cause passphrase encryption issues
■ Encryption Protocol Mismatch
● Encryption Protocols
○ WEP uses RC4
○ WPA uses TKIP
○ WPA2 uses AES
○ Network Security Key Mismatch
■ May indicate wrong password or using wrong encryption protocol
■ Solutions
● Manually change protocol
● Disable antivirus tools
● Reinstall wireless drivers
○ Ensure correct SSID, passphrase, and encryption protocol
○ If issues persist, investigate deeper OS or driver issues
● Captive Portal Issues
○ Captive Portal
■ Webpage displayed to newly connected users of a wireless network
before they're granted broader access to network resources
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CompTIA Network+
(N10-009) (Study Notes)
■ Purpose
● Authentication
● Payment
● Acceptance of agreements
● Survey completion
● Other information collection
○ Implementation
■ HTTP Redirect
● Redirects all traffic to a web server controlled by the network
● Uses 302 HTTP status code
■ ICMP Redirect
● Sends error messages and operational information indicating the
success or failure of communicating with another IP address
● Uses ICMP packets to redirect
● Less common
■ DNS Redirect
● Redirects to a captive portal page via DNS server
● Most common type
○ Common Issues
■ Smartphones and laptops may not automatically load the captive portal
● Troubleshooting steps for smartphones and laptops
○ Try opening a web browser
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CompTIA Network+
(N10-009) (Study Notes)
○ If that fails, enter the default gateway IP address in the
browser
○ Verify DNS server settings and enable DHCP if necessary
○ Captive portals are essential for controlling network access but can lead to issues
if not properly configured
● Wireless Considerations in Troubleshooting
○ Antennas
■ Types
● Omnidirectional
○ Radiates RF waves in all directions
○ Common in wireless APs
○ Located in vertical form factor
■ Vertical Antenna
● Radio frequency waves extend outward in
all directions away from the antenna and
the wireless access point at an equal power
level
● Dipole
○ Radiates RF waves in two directions
○ Less commonly used
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CompTIA Network+
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● Yagi
○ Unidirectional
○ Used for longer-distance wireless links
● Parabolic Grid/Disk
○ Unidirectional
○ Used for site-to-site connections over longer distances
■ Placement
● Site-to-site
○ Unidirectional antennas mounted outside with clear line of
sight
■ Parabolic
■ Yagi
● Indoor
○ Omnidirectional – placed on the ceiling
○ Unidirectional patch antennas – placed on an outer wall of
the building, facing inward
■ Polarization
● The orientation of of the electric field, or transmissions that are
occurring from the antenna
● Vertical polarization
○ Most Wi-Fi networks
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CompTIA Network+
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● Horizontal polarization
● Wireless access point could use vertical or horizontal polarization
● Poor RSSI near the access points could indicate polarization issues
○ Channel Utilization
■ A statistic or measure of airtime utilization for a frequency or channel
■ Higher utilization indicates more traffic
● Aim for under 30% to have faster wireless network
■ Overlapping channels can lead to congestion and slower speeds
■ Devices use CSMA/CA to avoid collisions and Clear Channel Assessment
(CCA) to assess channel availability
■ Site Survey
● Process of planning and designing wireless network to provide the
required wireless solution
● Helps determine optimal channel selection and coverage areas to
overcome the negative effect of having high channel utilization
○ Wireless Access Point Association Times
■ Seven-step process for client connection
● Wireless client sends a probe request
● Receiving access point checks to see if it can support the data rate
requested
● Wireless client sends a low-level authentication frame
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CompTIA Network+
(N10-009) (Study Notes)
● Access point receives the authentication frame and responds with
an acknowledgement
● Wireless client chooses the access point it wants to associate with
and sends association request
● Access point processes the association request
● Client is fully connected and associated
■ Association times can vary based on network load and signal strength
■ Faster association in high signal strength areas
■ Delay can be up to 30-60 seconds in busier networks

Wireless Network Troubleshooting and Performance Optimization

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