CWNA Guide to Wireless LANs, Second Edition

1. CWNA Guide to Wireless LANs, Second Edition Chapter Eleven 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 CWNA Guide to Wireless LANs, Second Edition

3. Wired Network Settings for Wireless Networks • All APs have RJ-45 connector that allows them to connect to an Ethernet hub or switch • Provide wired network resources to wireless devices • Settings for connecting to Ethernet network occasionally need to be adjusted • To improve wireless performance or provide additional capabilities • Mobile IP parameters can be set on APs CWNA Guide to Wireless LANs, Second Edition

4. Ethernet Parameters: Basic Settings Figure 11-1: Basic Ethernet settings CWNA Guide to Wireless LANs, Second Edition

5. Ethernet Parameters: Basic Settings (continued) • Allow wireless network administrators to designate Ethernet port as primary port of the AP • Select whether port “adopts” identity of primary port Table 11-1: Ethernet identification CWNA Guide to Wireless LANs, Second Edition

6. Ethernet Parameters: Advanced Settings Figure 11-2: Advanced DNS settings CWNA Guide to Wireless LANs, Second Edition

7. Ethernet Parameters: Advanced Settings (continued) • Setting on Figure 11-2: • Default Domain: Name of network’s IP domain • Current Domain: Domain that is serving the AP • IP addresses of up to three DNS servers can be entered under Domain Name Servers • Domain Suffix: Last portion of domain name of current network domain CWNA Guide to Wireless LANs, Second Edition

8. Ethernet Parameters: Advanced Settings (continued) Figure 11-3: Advanced Ethernet settings CWNA Guide to Wireless LANs, Second Edition

9. Ethernet Parameters: Filtering • Allows control of types of network traffic that pass from wired Ethernet network to WLAN devices • Configure AP to act as type of firewall • Different types of filtering: • Some devices filter at high level and can block an application from being requested • Other filtering can reject request for specific IP port • At the lowest level, filtering can look at received frames and block based on type of frame CWNA Guide to Wireless LANs, Second Edition

10. Ethernet Parameters: Filtering (continued) • Frames can be filtered by protocol used • e.g., TCP, UDP, IPX • Frames can be filtered by frame format • Four-character hexadecimal number found in each frame that indicates protocol and frame format Table 11-2: Frame formats CWNA Guide to Wireless LANs, Second Edition

11. Mobile IP Settings • Most WLAN implementations follow standard IP address plan • Single subnet for entire WLAN • Subnet: Portion of network that shares a common address component • Subnetting WLANs creates problems for users who roam between WLAN subnets • Cannot roam into new subnet without changing IP address • Need mechanism to ensure a device configured with specific IP address can continue to communicate when entering new subnet CWNA Guide to Wireless LANs, Second Edition

12. Mobile IP Settings (continued) Figure 11-4: Roaming between wireless subnets CWNA Guide to Wireless LANs, Second Edition

13. Mobile IP Settings (continued) • Mobile IP: Provides freedom to roam beyond home subnet while maintaining home IP address • AP forwards packets through Mobile IP enabled router to router on client’s home network • Five required devices: • Visiting device • Access point with Mobile IP enabled • Home agent • Authoritative access point • Foreign agent CWNA Guide to Wireless LANs, Second Edition

14. Mobile IP Settings (continued) • Mobile IP begins with home agents and foreign agents advertising their services • APs with Mobile IP enabled listen to advertisements • When visiting client associates to AP, AP compares client’s IP address with own IP network • Detects that client is a visitor • Begins registration • Gets home agent’s IP address by looking it up on a subnet map table CWNA Guide to Wireless LANs, Second Edition

15. Mobile IP Settings (continued) Table 11-3: Subnet map table CWNA Guide to Wireless LANs, Second Edition

16. Mobile IP Settings (continued) • Authoritative access point (AAP) responsible for maintaining/distributing master subnet map table of APs and home agent information • On some WLANs, may have multiple AAPs • When client roams to another network, foreign agent provides routing services • Assigns mobile client new temporary IP number • Care-of address • Registers care-of address with home agent • Home agent redirects frames to client via care-of-address CWNA Guide to Wireless LANs, Second Edition

17. 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 CWNA Guide to Wireless LANs, Second Edition

18. Solving RF Transmission Problems: Near/Far Figure 11-6: Near/far transmission problem CWNA Guide to Wireless LANs, Second Edition

19. 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 CWNA Guide to Wireless LANs, Second Edition

20. Solving RF Transmission Problems: Near/Far (continued) Figure 11-7: Signal strength CWNA Guide to Wireless LANs, Second Edition

21. 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 CWNA Guide to Wireless LANs, Second Edition

22. 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 CWNA Guide to Wireless LANs, Second Edition

23. 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 • Change the MAC layer • Change PHY layer • Best solutions is to not use the two devices together or migrate to 802.11a wireless technology CWNA Guide to Wireless LANs, Second Edition

24. 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 CWNA Guide to Wireless LANs, Second Edition

25. 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 CWNA Guide to Wireless LANs, Second Edition

26. 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 CWNA Guide to Wireless LANs, Second Edition

27. Solving RF Transmission Problems: Co-Location Throughput (continued) Figure 11-8: Adjacent Channels 1 and 6 CWNA Guide to Wireless LANs, Second Edition

28. 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 CWNA Guide to Wireless LANs, Second Edition

29. Solving RF Transmission Problems: Co-Location Throughput (continued) Figure 11-9: Separate channels CWNA Guide to Wireless LANs, Second Edition

30. 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 CWNA Guide to Wireless LANs, Second Edition

31. Solving Access Point Problems (continued) Table 11-4: Cisco Aironet LED information CWNA Guide to Wireless LANs, Second Edition

32. Solving Access Point Problems (continued) Table 11-4 (continued): Cisco Aironet LED information CWNA Guide to Wireless LANs, Second Edition

33. 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 CWNA Guide to Wireless LANs, Second Edition

34. 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 CWNA Guide to Wireless LANs, Second Edition

35. 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 CWNA Guide to Wireless LANs, Second Edition

36. 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 • Incorrect WEP key order • Mismatched pre-shared key • Conflict between Windows Wireless Auto Configuration and a third-party configuration tool • Incorrect MAC address CWNA Guide to Wireless LANs, Second Edition

37. 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 CWNA Guide to Wireless LANs, Second Edition

38. 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 CWNA Guide to Wireless LANs, Second Edition

39. Summary • Maintaining a wireless LAN involves adjusting the wired Ethernet settings to ensure peak performance • Most WLAN network implementations follow the standard Internet protocol (IP) address plan, which calls for a single subnet to be used for the entire WLAN • Mobile IP provides users the freedom to roam beyond their home subnets while still maintaining their home IP addresses CWNA Guide to Wireless LANs, Second Edition

40. 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 CWNA Guide to Wireless LANs, Second Edition

41. 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 CWNA Guide to Wireless LANs, Second Edition