Chapter 11 Network Settings and Wireless LAN Troubleshooting (Modified)

1
Chapter 11Network Settings and Wireless LAN
Troubleshooting (Modified)

• CCRI ENGR 1500

2
CWNA Guide to Wireless LANs, Second Edition

• Chapter Eleven
• Network Settings and Wireless LAN Troubleshooting
  (Modified)

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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

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Ethernet Parameters Basic Settings
Figure 11-1 Basic Ethernet settings
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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
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Ethernet Parameters Advanced Settings
Figure 11-2 Advanced DNS settings
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Ethernet Parameters Advanced Settings (continued)

• Setting on Figure 11-2
• Default Domain Name of networks 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

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Ethernet Parameters Advanced Settings (continued)
Figure 11-3 Advanced Ethernet settings
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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

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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
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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

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Mobile IP Settings (continued)
Mobile IP will be covered in another set of slides
Figure 11-4 Roaming between wireless subnets
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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

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Solving RF Transmission Near/Far Problem

• 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
• Possible Solutions
• 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

Netstubler-measure signal strength
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Solving RF All-Band Interference Problems

• FHSS uses range of frequencies that change during
  transmission
• Bluetooth 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
• Proposed Options for 802.11b/g and Bluetooth
• Change the RF spectrum, 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

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Solving System Throughput Problems

• 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
• 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
• Qcheck - Free tool for Throughput testing
• Install on end points

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Solving RF Transmission Problems Co-Location
Throughput
Possible Solutions -Change channels to
Channels 1 and 11 -Migrate to 802.11a 8
non-overlapping channels
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Solving RF Transmission Problems Co-Location
Throughput (continued)
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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
• All Aps have different test sequences
• Cisco, Linksys, Belkin, Netgear are all different

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Solving Access Point Problems

• 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

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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

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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

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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

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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
  network check box in Authentication tab
• Duplicate SSID
• Generally result of default SSID being used on
  APs
• Infection by computer virus
• Run antivirus software

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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

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Mobile IP Components
MN Mobile Node (VMD) FA Foreign Agent
(MAP) HA Home Agent (MAP) AAP Authoritative
Access Point MAP Mobile IP Access Point
(MN) VMD Visiting Mobile Device (MN) COA
Care-of-Address HAN Home Agent Network FAN
Foreign Agent Network CN Correspondent Node
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Subnets and Mobile IP

• Subnets provide many advantages
• make network management easier
• Subnets reduce broadcasts
• Subnets provide security
• Subnets use subnet masks (255.255.255.0)
• WLAN subnets creates problems for roaming devices
• Example
• 192.146.118.20 /24 can seamlessly roam within
  192.146.118.x /24
• Note /24 is a 255.255.255.0 subnet mask
• 192.146.118.20 /24 can not seamlessly roam within
  202.165.200.x /24 without changing the IP address
• Mobile IP offers a solution
• 192.146.118.20 can roam as a guest on the
  202.165.200.x network

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Mobile IP Devices

• Visiting Device
• Some APs support Mobile IP and Visiting devices
• Mobile IP Access Point
• Performs all Mobile IP services
• Home Agent
• Visiting devices home router
• Tunnels packets from visited network to
  visiting device
• Authoritative Access Point (AAP)
• Uses a subnet map to track all home visiting
  devices
• Foreign Agent
• A router the is the attachment point for
  visiting devices
• Tunnels packets to the Home Agent for the
  visiting device

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Mobile IP Process - Discovery
Mobile IP 3-Step Process 1-Discovery 2-Registratio
n 3-Tunneling
2
MN Mobile Node FA Foreign Agent HA Home
Agent
3
1
4
1- Mobile Node (MN) gets address from Home Agent
(HA) 2- MN moves to Foreign Agent (FA )
network 3- MN discovers FA or solicits for an
agent. 4- MN gets Care-of-Address (COA) from FA
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Mobile IP Process - Registration
Mobile IP 3-Step Process 1-Discovery 2-Registratio
n 3-Tunneling
5
10
7
12
8
6
9
MN Mobile Node FA Foreign Agent HA Home
Agent CN Correspondent Node
11
5- MN send registration request to FA 6- FA
checks request, adds MN to pending list 7- FA
relays request to HA 8- HA checks request and
creates a mobile binding 9- HA sends registration
reply to FA
10- FA checks reply and adds MN to visitor list
and relays reply to MN 11-FA creates a routing
entry and tunnel to HA 12- MN check reply and
creates a tunnel to the HA Through the FA
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Mobile IP- Tunneling and Packet Forwarding

MN Mobile Node FA Foreign Agent HA Home
Agent CN Correspondent Node COA- Care-of-Address
                                                  
                                                  
13
14
15
13- Correspondent Node (CN) sends packet to MN
and is routed to HA 14- HA intercepts packets and
tunnels to the FA using the COA 15- FA relays the
packets to the MN
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Mobile Node Movement
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Wireless Test Equipment and White Papers

• Many companies supply wireless test equipment
• Cisco
• Fluke
• Ixia
• Others
• See List of White Papers relating to Wireless
  testing

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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

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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

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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