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Lecture 8. Network Settings and Wireless LAN Troubleshooting. Objectives. Explain the wired network settings that can be modified in a wireless network List troubleshooting techniques for solving RF transmission problems Describe how to solve access point problems

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lecture 8

Lecture 8

Network Settings and Wireless LAN Troubleshooting

objectives
Objectives
  • Explain the wired network settings that can be modified in a wireless network
  • List troubleshooting techniques for solving RF transmission problems
  • Describe how to solve access point problems
  • Describe the types of wireless device problems and explain how to solve them
troubleshooting wireless networks
Troubleshooting Wireless Networks
  • Troubleshooting can be difficult with WLANs
    • Many factors can impact wireless transmissions
      • Many of them are “non-technical”
    • Technology is relatively new
    • Problems can be result of anything from overlooking check box on a dialog box to metal objects in path of RF signal
  • Categorized into identifying and solving problems with RF transmissions, APs, and wireless devices
solving rf transmission problems near far
Solving RF Transmission Problems: Near/Far

Figure 11-6: Near/far transmission problem

solving rf transmission problems near far continued
Solving RF Transmission Problems: Near/Far (continued)
  • Two steps to identify device that is a victim of near/far transmission problem
    • Wireless protocol analyzer running on a device displays signal strength
      • Low signal strength may indicate problem
        • May not indicate near/far problem
        • Also determine signal strength on nearby devices
    • Review placement of wireless devices
solving rf transmission problems near far continued2
Solving RF Transmission Problems: Near/Far (continued)
  • Several solutions to near/far transmission problems:
    • Move device with stronger transmission power farther away from AP
    • Reduce transmission power of devices closer to AP
    • Increase transmission power of devices farther away from AP
solving rf transmission problems all band interference
Solving RF Transmission Problems: All-Band Interference
  • FHSS uses range of frequencies that change during transmission
    • Bluetooth, for example, is a close-range, frequency hopping technology that operates in same 2.4 GHz ISM band as IEEE 802.11b/gWLANs
      • Can create all-band interference
    • IEEE 802.11b/g and Bluetooth devices do not “peacefully coexist” in same environment
solving rf transmission problems all band interference continued
Solving RF Transmission Problems: All-Band Interference (continued)
  • Several options have been proposed for 802.11b/g and Bluetooth to work together:
    • Change the RF spectrum used
    • Modify power levels
    • Add switching software
  • Best solutions is to not use the two devices together or migrate to 802.11a wireless technology
solving rf transmission problems system throughput
Solving RF Transmission Problems: System Throughput
  • Many factors influence WLAN transmission speed:
    • AP processor speed
    • Distance from AP
    • Implementing security solutions
    • Number of users associated with an AP
    • Packet size
    • RTS/CTS protocol
    • Types of RF interference
    • Using PCF protocol
solving rf transmission problems system throughput continued
Solving RF Transmission Problems: System Throughput (continued)
  • To troubleshoot:
    • Determine if all devices experiencing problem or only a single device
    • Identify potential causes that may have least impact on system if changed
solving rf transmission problems co location throughput
Solving RF Transmission Problems: Co-Location Throughput
  • When a mobile wireless user enters into range of more than one AP, wireless device will choose an AP based on signal strength or packet error rates
    • For 802.11b and 802.11g wireless LANs only channels 1, 6, and 11 can be used to co-locate multiple APs in same area
  • Small amount of overlap between channels 1 and 6, as well as between channels 6 and 11
    • Co-location throughput
    • Can affect wireless network performance
solving rf transmission problems co location throughput continued
Solving RF Transmission Problems: Co-Location Throughput (continued)

Figure 11-8: Adjacent Channels 1 and 6

solving rf transmission problems co location throughput continued1
Solving RF Transmission Problems: Co-Location Throughput (continued)
  • Possible solutions:
    • Change channels to Channels 1 and 11
    • Migrate to 802.11a
      • 8 non-overlapping channels
solving rf transmission problems co location throughput continued2
Solving RF Transmission Problems: Co-Location Throughput (continued)

Figure 11-9: Separate channels

solving access point problems
Solving Access Point Problems
  • All APs have external light emitting diodes
    • Ethernet indicator: Signals traffic on wired LAN
      • Green when Ethernet cable is connected
      • Blinks green when packet received or transmitted
      • Off when Ethernet cable not connected
    • Status indicator: Signals operational status
      • Green indicates AP associated with at least one wireless device,
      • Blinking green means AP operating normally but is not associated with any wireless devices
    • Radio indicator: Blinks green to indicate RF activity
solving access point problems continued
Solving Access Point Problems (continued)

Table 11-4: Cisco Aironet LED information

solving access point problems continued1
Solving Access Point Problems (continued)

Table 11-4 (continued): Cisco Aironet LED information

solving access point problems continued2
Solving Access Point Problems (continued)
  • If AP does not communicate with devices, check:
    • SSID
    • WEP keys
    • Security settings
  • In extreme circumstances, may be necessary to delete current AP configuration and return all settings to factory defaults
solving wireless device problems wireless device connection process
Solving Wireless Device Problems: Wireless Device Connection Process
  • Five-step connection process:
    • Scan for access points
      • Wireless network adapter sends series of Probe Request frames
      • APs within range respond with Beacon frame that contains the capabilities of the wireless AP
    • Choose an access point
      • Decision based on:
        • Wireless AP capabilities
        • SSID matches a preferred network
        • Signal strength
solving wireless device problems wireless device connection process continued
Solving Wireless Device Problems: Wireless Device Connection Process (continued)
  • Five-step connection process (continued):
    • Authenticate with the access point
      • Type of authentication depends on security capabilities of AP and how wireless device has configured to authenticate with AP
    • Associate with the access point
    • Obtain an IP address
      • Manual addressing
      • DHCP addressing
      • APIPA addressing
solving wireless device problems troubleshooting wireless devices
Solving Wireless Device Problems: Troubleshooting Wireless Devices
  • Possible causes if problems makings connection:
    • Incompatible IEEE 802.11 standards
    • Mismatched authentication methods
    • Different WEP keys
      • Will not prevent association, but will prevent successful communication
    • Mismatched pre-shared key
    • Conflict between Windows Wireless Auto Configuration and a third-party configuration tool
    • Incorrect MAC address
solving wireless device problems troubleshooting wireless devices continued
Solving Wireless Device Problems: Troubleshooting Wireless Devices (continued)
  • Possible causes if wireless device intermittently disconnects from AP:
    • Incompatible 802.1x authentication
      • For computers running Windows XP with SP1, clear Enable IEEE 802.1x authentication for this networkcheck box in Authentication tab
    • Duplicate SSID
      • Generally result of default SSID being used on APs
    • Infection by computer virus
      • Run antivirus software
solving wireless device problems troubleshooting wireless devices continued1
Solving Wireless Device Problems: Troubleshooting Wireless Devices (continued)
  • Possible causes if wireless device intermittently disconnects from AP (continued):
    • Faulty hardware
      • Run diagnostic tests for AP or wireless network adapter
      • Use current drivers
    • Wireless attacks
      • May require special scanners to pinpoint attacker
    • Device misconfiguration
summary continued
Summary (continued)
  • A device that is transmitting at higher signal strength and is located closer to the access point will drown out a weaker signal from a device that is farther away and is using less power
  • Technologies such as Bluetooth which use the entire 2.4 GHz spectrum can impact IEEE 802.11 WLANs that use the same frequency spectrum
  • Co-location throughput can affect the performance of access points that use 802.11b/g technology because of channel overlap on channels 1, 6, 11
summary continued1
Summary (continued)
  • Solving access point problems often starts with observing the LED lights that provide information regarding Ethernet and RF activity along with operational status
  • Wireless device problems fall into two broad categories: the inability to make a successful wireless connection and intermittently disconnecting from the access point
slide27
LAB
  • LAB E
  • LAB F
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