Lecture 8

1. Lecture 8 Network Settings and Wireless LAN Troubleshooting

2. 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

3. 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

4. Solving RF Transmission Problems: Near/Far Figure 11-6: Near/far transmission problem

5. 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

6. Solving RF Transmission Problems: Near/Far (continued) Figure 11-7: Signal strength

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. Solving RF Transmission Problems: Co-Location Throughput (continued) Figure 11-8: Adjacent Channels 1 and 6

14. 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

15. Solving RF Transmission Problems: Co-Location Throughput (continued) Figure 11-9: Separate channels

16. 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

17. Solving Access Point Problems (continued) Table 11-4: Cisco Aironet LED information

18. Solving Access Point Problems (continued) Table 11-4 (continued): Cisco Aironet LED information

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. LAB • LAB E • LAB F