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Chapter 11
Network Settings and Wireless LAN
Troubleshooting (Modified)
CCRI ENGR 1500
CCRI
J. Bernardini
1
CWNA Guide to Wireless LANs,
Second Edition
Chapter Eleven
Network Settings and Wireless LAN
Troubleshooting (Modified)
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
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Ethernet Parameters: Basic Settings
Figure 11-1: Basic Ethernet settings
CWNA Guide to Wireless LANs,
Second Edition
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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
CWNA Guide to Wireless LANs, Second Edition
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Ethernet Parameters: Advanced
Settings
Figure 11-2: Advanced DNS settings
CWNA Guide to Wireless LANs,
Second Edition
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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
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Ethernet Parameters: Advanced
Settings (continued)
Figure 11-3: Advanced Ethernet settings
CWNA Guide to Wireless LANs,
Second Edition
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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
CWNA Guide to Wireless LANs,
Second Edition
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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
CWNA Guide to Wireless LANs, Second Edition
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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
CWNA Guide to Wireless LANs,
Second Edition
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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
CWNA Guide to Wireless LANs,
Second Edition
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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
CWNA Guide to Wireless LANs,
Second Edition
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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
Netstublermeasure signal
strength
CWNA Guide to Wireless LANs,
Second Edition
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•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
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
CWNA Guide to Wireless LANs,
Second Edition
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Solving System Throughput Problems
• Many factors influence WLAN transmission speed:
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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
CWNA Guide to Wireless LANs,
Second Edition
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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
CWNA Guide to Wireless LANs,
Second Edition
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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
CWNA Guide to Wireless LANs,
Second Edition
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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
CWNA Guide to Wireless LANs,
Second Edition
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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
CWNA Guide to Wireless LANs,
Second Edition
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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 thirdparty configuration tool
– Incorrect MAC address
CWNA Guide to Wireless LANs,
Second Edition
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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
CWNA Guide to Wireless LANs,
Second Edition
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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
CWNA Guide to Wireless LANs,
Second Edition
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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
CCRI
J. Bernardini
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Subnets and Mobile IP
• Subnets provide many advantages:
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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
CCRI
J. Bernardini
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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
CCRI
J. Bernardini
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Mobile IP Process - Discovery
Mobile IP
2
3-Step Process
1-Discovery
2-Registration
MN – Mobile Node
FA – Foreign Agent
3
1
4
HA – Home Agent
3-Tunneling
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
CCRI
J. Bernardini
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Mobile IP Process - Registration
Mobile IP
3-Step Process
1-Discovery
12
10
2-Registration
5
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6
9
8
11
3-Tunneling
MN – Mobile Node
FA – Foreign Agent
HA – Home Agent
CN – Correspondent Node
5- MN send registration request to FA
6- FA checks request, adds MN to pending list
10- FA checks reply and adds MN to visitor list and
relays reply to MN
7- FA relays request to HA
11-FA creates a routing entry and tunnel to HA
8- HA checks request and creates a mobile binding
12- MN check reply and creates a tunnel to the HA
9- HA sends registration reply to FA
Through the FA
CCRI
J. Bernardini
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Mobile IP- Tunneling and Packet
Forwarding
MN – Mobile Node
FA – Foreign Agent
HA – Home Agent
13
CN – Correspondent Node
COA- Care-of-Address
14
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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
CCRI
J. Bernardini
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Mobile Node Movement
CCRI
J. Bernardini
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Wireless Test Equipment and White
Papers
• Many companies supply wireless test equipment
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Cisco
Fluke
Ixia
Others
• See List of White Papers relating to Wireless testing
CCRI
J. Bernardini
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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
CWNA Guide to Wireless LANs,
Second Edition
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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
CWNA Guide to Wireless LANs,
Second Edition
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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
CWNA Guide to Wireless LANs,
Second Edition
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