Transcript Service Set Identification (SSID)

Wireless Networking
Chapter 9
Contents
• Explain wireless networking hardware and
software requirements and configure wireless
networking hardware
• Define wireless networking IEEE standards and
FCC operation frequencies
• Define wireless network operation modes, limits,
and methods
• Configure wireless networking security
• Describe troubleshooting techniques for
wireless networks
Introduction
Wireless Networking
• Wireless networking uses radio waves instead of
wires to connect devices
• Wireless networking is dominated by two
technologies
– IEEE 802.11 wireless Ethernet standard
• Wireless Fidelity (Wi-Fi)
• Home Radio Frequency (HomeRF)
– Bluetooth
Wireless Networking Basics
Hardware
• Wireless Ethernet
NICs and Bluetooth
adapters serve the
same purpose as
hardware in wired
networks
• Many wireless PCI
NICs are simply
wireless PC Card
NICs housed on a PCI
card
USB Wireless NICs
• Have the benefit of being placeable – able to
move them around to get the best signal
– Like moving the rabbit ears on an old TV set
Adapters
• Used by not just PCs but also printers, handheld
computers, and PDAs
Access Points
• If you’re connecting a small group of PCs
together in a decentralized workgroup, then the
wireless NICs are all you need
• If you wish to expand your network or to
connect it to a wired network, you’ll need a
wireless access point
Wireless Bridges
• Wireless bridges connect two different wireless
segments or a wireless segment to a wired
network
– Point-to-Point bridges can only communicate with a
single other bridge
– Point-to-Multipoint bridges can talk to more than one
bridge at a time
Bluetooth Hardware
• Wireless Bluetooth hardware is included as
built-in equipment in many PCs, laptops, PDAs,
and cell phones
• Most Bluetooth add-on devices are USB
External USB
Bluetooth adapter
Software
• Wireless adapters come
with a driver and a
configuration utility
– Windows XP comes with
drivers and configuration
utilities for wireless
– The utility that came with
the card is better to use
– Browser-based utilities
are common
Ad-hoc Mode
• Ad-hoc mode
–
–
–
–
Also called peer-to-peer mode
Each node directly contacts other nodes
Used for small networks
Two or more wireless nodes talking in ad-hoc mode
form an Independent Basic Service Set (IBSS)
Infrastructure Mode
• Infrastructure mode
– Use one or more wireless access points to connect
the nodes centrally
– Provides centralized control
– Used for larger networks
– A single wireless access
point servicing a give area
is called a Basic Service
Set (BSS)
– Add more access points to
form an Extended Basic
Service Set (EBSS)
Security
• Wireless networking devices provide no security
out of the box
• Hackers may easily grab packets right out of the
air and read them
• To provide better security, wireless networks
use one of these methods:
– Service Set Identification (SSID) or network names
– Media Access Control address filtering
– Data encryption
Service Set Identification
• The Service Set Identification (SSID) is a 32-bit
string in the header of each packet
• Only wireless clients whose SSID matches can
gain access to the network
• Wireless access points come with a generic
SSID that is widely publicized by the vendor
– Linksys uses linksys
– 3Com uses 101
– Netgear uses wireless or netgear
MAC Filtering
• MAC address filtering limits access based on the
physical, hard-wired address of the wireless
network adapter
• Any data packet whose MAC address is not
listed in the wireless access point’s table is
rejected
• Specified MAC addresses may be denied
• MAC addresses may be spoofed by hackers
• Each MAC address needs to be manually
entered initially and kept up to date
Encryption
• Encrypted data packets are electronically
scrambled (locked) with a private encryption key
before being transmitted
• The receiving device must possess the
encryption key in order to unscramble (unlock)
the packet
• Encryption is enabled through Wireless
Equivalency Privacy (WEP) or Wi-Fi Protected
Access (WPA) or WPA2
Wireless Equivalency
Privacy
• WEP uses a 64-bit encryption algorithm
• Works only on layers 1 and 2 (Physical and Data
Link)
• Encryption key is static (same from session to
session) and shared by all network nodes
• No user authentication
Wi-Fi Protected Access
• WPA offers
– Dynamic encryption key generation issued on a peruser, per-session basis
– Encryption key integrity-checking feature
– User authentication through Extensible Authentication
Protocol (EAP)
– Not available on all wireless devices
Speed
• Ranges from 2 Mbps to 54 Mbps
• Speed decreases as distance increases
• Speed is affected by interference from other
networking devices and solid objects
– Dead spots may be created by things like
refrigerators, air conditioners, metal plumbing
Range
• Environmental factors greatly affect range
• Theoretical maximum ranges are usually listed,
while the effective range may be about half as
far
• To extend range:
– Add more wireless access points
– Install a signal booster to increase the WAP’s signal
Broadcasting Frequencies
• The Federal Communications Commission (FCC)
set aside the Industrial, Scientific, and Medical
(ISM) frequencies for wireless networking
– 83.5 MHz of bandwidth in the 2.4 GHz frequency band
– 125 MHz of bandwidth in the 5.8 GHz band
– 300 MHz of bandwidth (Unlicensed National
Information Infrastructure (U-NII)) split into:
• 5.15 to 5.25 GHz frequency band
• 5.25 to 5.35 GHz frequency band
• 5.725 to 5.825 GHz frequency band
Media Access Methods
• Multiple devices may share a medium by first
listening in on the network media to see if it is
busy
• Devices need to wait if it is busy for the length of
a frame plus the Interframe Space (IFS)
• If two devices transmit at the same time a
collision occurs and data is corrupted
• How are collisions dealt with?
CSMA/CD
• Carrier Sense Multiple Access /Collision
Detection
– When a collision occurs (is detected), the device will
wait a random amount of time and then attempt to
resend the data
CSMA/CA
• Carrier Sense Multiple Access / Collision
Avoidance
– Instead of reacting to collisions, steps are taken to
avoid collisions using Distributed Coordination
Function (DCF)
• Point Coordination Function (PCF) is defined but not implemented
yet
– DCF requires receiving nodes to send an
Acknowledgement (ACK) for every packet that tells
other nodes to wait a certain amount of time before
trying to access the media
RTS/CTS
• Request To Send/Clear To Send (RTS/CTS)
– Transmitting nodes send an RTS frame to the
receiving node before transmitting any data
– The receiving node responds with a CTS
– Another form of collision avoidance
Wireless Networking Standards
802.11 Standard
• IEEE 802.11 wireless Ethernet standard defines
methods to communicate using spreadspectrum radio waves
– Broadcast data in small discrete chunks within a
frequency range
• All 802.11 wireless technologies use the 2.4 GHz frequency
• Except for 802.11a that uses the 5 GHz frequency
Broadcasting Methods
• Direct-sequence spreadspectrum (DSSS)
– Sends data out on
difference frequencies at
the same time
– Uses 22 MHz bandwidth
– Greater throughput
– More prone to
interference
– Used by most 802.11based wireless
networking standards
• Frequency-hopping
spread-spectrum (FHSS)
– Sends data on one
frequency at a time
– Constantly shifts or hops
frequencies
– Uses 1 MHz bandwidth
– Used by HomeRF
wireless networks
Wi-Fi Standards
• Most widely adapted wireless networking
technology today
• Devices that conform to the extended versions
of the 802.11 standard (802.11a, 802.11b, and
802.11g) are Wi-Fi certified
– By the Wi-Fi Alliance (formerly the Wireless Ethernet
Compatibility Alliance – WECA)
• Wireless devices must use the same standard to
communicate
– 802.11g is backwards compatible with 802.11b
802.11
•
•
•
•
•
•
The original standard
Slow speed at 2 Mbps
Limited range at about 150 feet
Uses the 2.4 GHz broadcast range
Security provided by WEP and WPA encryption
Rare today
802.11a
• Operates in the 5 GHz frequency range with 8
available channels
• Less crowded frequency range which reduces
the chances of interference
• Speeds up to 54 Mbps
• Maximum range is around 150 feet
• Developed after 802.11b
• Not widely adopted
802.11b
•
•
•
•
Throughput up to 11 Mbps
Range up to 300 feet
Security through WEP and WPA encryption
Uses the 2.4 GHz frequency range with 14
available channels (11 in the U.S.)
• Most widely used today which makes it more
likely to suffer from interference
802.11g
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•
•
•
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Throughput up to 54 Mbps
Range up to 300 feet
Backwardly compatible with 802.11b
Newest version
Operates in 2.4 GHz range with 14 available
channels (11 in the U.S.)
802.11 Standards
Standard
802.11
802.11a
802.11b
802.11g
Maximum
Throughput
2 Mbps
54 Mbps
11 Mbps
54 Mbps
Maximum Range
150 feet
150 feet
300 feet
300 feet
Frequency
2.4 GHz
5 GHz
2.4 GHz
2.4 GHz
Compatibility
802.11
802.11a
802.11b
802.11b,
802.11g
802.11 Standards
Standard
802.11N
Maximum
Throughput
300 Mbps
Maximum Range
150 feet
Frequency
2.4 GHz, 5GHZ
Compatibility
802.11a, 802.11bg,
802.3a/b, 802.3a/f,
802.3u and 802.3
standards.
802.11 Standards
• Security methods used by all:
– SSID
– MAC filtering
– Industry standards WEP, WPA
• Spread-spectrum method used by all:
– DSSS
• Communication modes supported by all:
– Ad-hoc
– Infrastructure
HomeRF
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•
•
•
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Intended for home usage
Maximum range of 150 feet
Maximum speed of 2 Mbps
Version 2 maximum speed of 10 Mbps
Uses FHSS spread-spectrum broadcasting
method – making it less susceptible to
interference
• Uses a Network ID (NWID)
• 56-bit encryption algorithm
• 7 channels in the 2.4 GHz range (6 for voice, 1
for data)
Bluetooth
• Bluetooth creates small wireless networks called
Personal Area Networks (PANs) between PCs
and peripheral devices
– PDAs, printers, keyboards, mice, cell phones, home
stereos, televisions, home security systems
• Basis for upcoming IEEE 802.15 standard
• Throughput from 723 Kbps to 1 Mbps
• Maximum range of 10 meters (33 feet)
Bluetooth Operation Modes
• Operates in an automatic master/slave
relationship
– One master controls up to seven slave devices
– A Bluetooth PAN is called a piconet (meaning very
small)
– Up to 255 devices may participate but only seven may
be active at a time
– An inactive slave device is called a parked device
Bluetooth Communication
Stages
• Device discovery
– Broadcasts its MAC address an a code identifying the type
of device
– May set device to non-discovery mode to skip this stage
• Name discovery
– Device identifies itself by a friendly name
• Such as iPAQ Pocket PC
• Association
– Device officially joins the network
– Some devices require a PIN code for security
– Also called bonding, pairing, or joining
• Service profile
– Defines the kind of service it provides
My Bluetooth Places
Data Transfer
• Synchronous ConnectionOriented (SCO)
– Guarantees all data
transmitted is received
– Good for file transfers
– Master nodes support up
to 3 SCO connections at
a time with up to 3 slave
units
• Asynchronous
Connectionless (ACL)
– No guarantee of delivery
– Faster
– Good for streaming
media
– Point-to-point (master to
slave) or broadcast
(master to all slaves)
links
Bluetooth Services
• Services supported by Bluetooth are called
profiles
– Generic Access Profile defines how units discover and
establish connections
– Service Discovery Profile enables discovery of
services other devices provide
– Cordless Telephony Profile defines wireless phone
functionality
– Intercom Profile defines wireless intercom
functionality
– Serial Port Profile enables a device to emulate serial
port communication
– Headset Profile defines wireless telephone and PC
headset functionality
Bluetooth Services
– Dial-up Networking Profile defines capability to act as
or interact with a modem
– Fax Profile defines capability to act as or interact with
a fax device
– LAN Access Profile defines how a device accesses a
LAN or the Internet
– Generic Object Exchange Profile defines how to
exchange data with other devices
– Object Push Profile is used to exchange small data
objects
– File Transfer Profile is used to exchange large data
objects like files
– Synchronization Traffic is used to synchronize data
between PDAs and PCs
Bluetooth Services
Bluetooth Security
• 128-bit encryption and per-user passwords
• Point-to-Point Tunneling Protocol (PPTP) and
Secure Sockets Layer (SSL) for browser-based
remote access
• MAC filtering
• Non-discovery mode to hide them from other
devices
Configuring Wireless Networking
Wi-Fi and HomeRF
• Install a wireless network adapter the same way
as a wired adapter
• Check Windows Device Manager after
installation
Configuring Ad-Hoc Mode
• Each wireless node must use the same network
name (SSID)
• No two nodes can have the same IP address
• Ensure that File and Printer Sharing is running
on all nodes
Ad-Hoc Mode
Configuring Infrastructure Mode
• Configure the same
SSIC on all nodes
and the access point
• You may also
configure DHCP
options, filtering,
client channels, and
more
Access Point Configuration
• Uses a browser-based setup utility
• Point web browser to 192.168.1.1 and use the
administrative password given in the
documentation
• Various configuration options will be available
such as SSID and whether to broadcast it
Access Point Configuration
Configuring MAC Filtering
Configuring Encryption
Encryption on Wireless NIC
Bluetooth Hardware
• Comes integrated with many devices today
• To add Bluetooth capabilities you usually need
to install an adapter
– Follow the instructions which usually require you to
install your driver and configuration utility first
– Bluetooth devices seek each other out and establish
master/slave relationships automatically
Connecting to PAN
iPAQ Bluetooth
Manager software
connected to
Bluetooth access
point
Bluetooth Access Point
Troubleshooting Wireless Networks
Scope of Problem
• Who is affected by the problem?
– Try to isolate whether the problem relates to a few
client machines or to an access point
• What is the nature of their network problem?
– Can some network services to accessed while others
cannot? Then the problem is most likely not related to
their client equipment
• When did the problem start?
– What changed?
Wi-FI and HomeRF
• Hardware
– Check Device Manager for resource conflicts
– Try reinstalling the device driver
• Software
– USB devices usually require that you first install the
software before the hardware
– Update the device’s firmware version to the latest
Connectivity
• Check the link light
• Check the configuration utility for link state and
signal strength
• There could be interference or a weak signal
Configuration
• Check your SSID and WEP configuration for
typos
– Watch for blank spaces at the end of a SSID
• Make sure the MAC address of the client is on
the list of accepted users
• Make sure the encryption strength matches
Bluetooth
• Hardware
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–
–
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Check for detection, driver or resource errors
Make sure the device is seated properly
Some newer Bluetooth devices only work with USB 2.0
Check Device Manager
• Software
– Always check the documentation before installing
Bluetooth devices – sometimes steps may not be
performed out of order
– Only Windows XP (with service pack 1) and Apple OSX
offer native support for Bluetooth
Connectivity & Configuration
• Check the configuration utility
• Remember Bluetooth range is limited to 30 feet
• Shut down other Bluetooth devices in the same
area to see if there is interference
• Make sure all device use the same profile
• Check to see if non-discovery mode has been
enabled
• Check the password or PIN
• Check the power-saving settings