Lecture 8
This presentation is the property of its rightful owner.
Sponsored Links
1 / 27

Lecture 8 PowerPoint PPT Presentation


  • 83 Views
  • Uploaded on
  • Presentation posted in: General

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

Download Presentation

Lecture 8

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


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 continued1

Solving RF Transmission Problems: Near/Far (continued)

Figure 11-7: Signal strength


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


Lecture 8

LAB

  • LAB E

  • LAB F


  • Login