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CWNA Guide to Wireless LANs, Second Edition. Chapter Eleven 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

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Cwna guide to wireless lans second edition

CWNA Guide to Wireless LANs, Second Edition

Chapter Eleven

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

CWNA Guide to Wireless LANs, Second Edition


Wired network settings for wireless networks
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


Ethernet parameters basic settings
Ethernet Parameters: Basic Settings

Figure 11-1: Basic Ethernet settings

CWNA Guide to Wireless LANs, Second Edition


Ethernet parameters basic settings continued
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


Ethernet parameters advanced settings
Ethernet Parameters: Advanced Settings

Figure 11-2: Advanced DNS settings

CWNA Guide to Wireless LANs, Second Edition


Ethernet parameters advanced settings continued
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


Ethernet parameters advanced settings continued1
Ethernet Parameters: Advanced Settings (continued)

Figure 11-3: Advanced Ethernet settings

CWNA Guide to Wireless LANs, Second Edition


Ethernet parameters filtering
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


Ethernet parameters filtering continued
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


Mobile ip settings
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


Mobile ip settings continued
Mobile IP Settings (continued)

Figure 11-4: Roaming between wireless subnets

CWNA Guide to Wireless LANs, Second Edition


Mobile ip settings continued1
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


Mobile ip settings continued2
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


Mobile ip settings continued3
Mobile IP Settings (continued)

Table 11-3: Subnet map table

CWNA Guide to Wireless LANs, Second Edition


Mobile ip settings continued4
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


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

CWNA Guide to Wireless LANs, Second Edition


Solving rf transmission problems near far
Solving RF Transmission Problems: Near/Far

Figure 11-6: Near/far transmission problem

CWNA Guide to Wireless LANs, Second Edition


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

CWNA Guide to Wireless LANs, Second Edition


Solving rf transmission problems near far continued1
Solving RF Transmission Problems: Near/Far (continued)

Figure 11-7: Signal strength

CWNA Guide to Wireless LANs, Second Edition


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

CWNA Guide to Wireless LANs, Second Edition


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

CWNA Guide to Wireless LANs, Second Edition


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

    • 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


Solving rf transmission problems system throughput
Solving RF Transmission Problems: System Throughput (continued)

  • 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


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

CWNA Guide to Wireless LANs, Second Edition


Solving rf transmission problems co location throughput
Solving RF Transmission Problems: Co-Location Throughput (continued)

  • 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


Solving rf transmission problems co location throughput continued
Solving RF Transmission Problems: Co-Location Throughput (continued)

Figure 11-8: Adjacent Channels 1 and 6

CWNA Guide to Wireless LANs, Second Edition


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

CWNA Guide to Wireless LANs, Second Edition


Solving rf transmission problems co location throughput continued2
Solving RF Transmission Problems: Co-Location Throughput (continued)

Figure 11-9: Separate channels

CWNA Guide to Wireless LANs, Second Edition


Solving access point problems
Solving Access Point Problems (continued)

  • 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


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

Table 11-4: Cisco Aironet LED information

CWNA Guide to Wireless LANs, Second Edition


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

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

CWNA Guide to Wireless LANs, Second Edition


Solving access point problems continued2
Solving Access Point Problems (continued) (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


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

CWNA Guide to Wireless LANs, Second Edition


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

CWNA Guide to Wireless LANs, Second Edition


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

    • 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


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

CWNA Guide to Wireless LANs, Second Edition


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

CWNA Guide to Wireless LANs, Second Edition


Summary
Summary Devices (continued)

  • 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


Summary continued
Summary (continued) Devices (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


Summary continued1
Summary (continued) Devices (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