Wireless Technologies
Networking for Home and Small Businesses – Chapter 7
Spring 2009 - Mr. Specter
ITE PC v4.0
Chapter 1
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
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Objectives:
 Describe wireless technologies.
 Describe the various components and structure
of a WLAN
 Describe wireless LAN security issues and
mitigation strategies
 Configure an integrated wireless access point
and a wireless client .
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Electromagnetic Frequencies
 All use waves in the Electromagnetic spectrum to transfer
information from device to device.
 Electromagnetic spectrum includes bands used for radio, TV,
and visible light.
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Wireless Technologies
 Infrared Band (IR)
– Low energy and unable to penetrate walls (line of sight)
• Could this be a benefit?
– Used for PDAs, PCs, wireless mice, keyboards and remote controls
– IrDA (Infrared Direct Access) port used for 1 to 1 connections
 Radio Frequency (RF)
– Goes through walls and other obstructions, better range
– Different frequencies assigned to different types of unlicensed devices
(900MHz, 2.4GHz, 5GHz)
• Cordless Phones
– Problem with 900MHz?
– Used for military and civilian emergency bands outside US
• Wireless LANs
• Computer Peripherals
• Bluetooth uses 2.4 GHz band for low-speed, short-range, many
devices at once
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Wireless Technologies
 Pros
 Cons
– Anytime, anywhere connectivity with
hotspots
– Easy and cheap installation
– Device prices dropping
– Data rate capabilities increasing
– Easy expansion
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– Unlicensed RF which is crowded
with other devices
• Bluetooth
• Microwaves
• Cordless phones
– Security is difficult because there is
no way to limit who can intercept the
wireless signal
• Encryption helps, but can be
defeated
– Fluctuations in temperature and
humidity can really affect
transmission range.
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Wireless Network Categories
 Wireless networks are difficult to categorize because boundaries cannot be
precisely defined.
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Wireless Network Technologies
 Technologies used for the different network types:
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WLAN Standards
 Many different standards have been adopted for wireless
networks
– IEEE 802.11n is latest standard adopted (except for 802.11y)
– Wi-Fi Alliance tests devices from various manufacturers to make sure they
operate together.
Protocol Release
Date
RF
Freq.
Through
put
Data
Rate
(Max)
Max
Range
Notes & Comments
802.11
1997
2.4 GHz 0.9 Mbps 2 Mbps
Undefined Legacy
802.11a
1999
5 GHz
50m
Not compatible with b, g, n
Expensive
802.11b
1999
2.4 GHz 4.3 Mbps 11 Mbps
100m
First 2.4 GHz Technology
802.11g
2003
2.4 GHz 19 Mbps 54 Mbps
100m
Backward compatible with b
Shares range with b
802.11n
2009*
2.4 & 5
GHz
802.11y
2008*
3.7 GHz 23 Mbps 54 Mbps
23 Mbps 54 Mbps
74 Mbps 248 Mbps 250m
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5000m
Newest Standard
Newest Standard
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Structure of a WLAN
 Wireless Components
– Wireless Clients or
STAs (Wireless
STAtion)
– APs (Access Points)
– Wireless Bridges
 Types of Antennas
– Omni send all
directions
• Used in APs
– Directional send in one
direction
• Used for longer
links to bridge
distances
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WLAN Types
 The Service Set Identifier
(SSID) used by components
to connect to a particular
WLAN.
– 32-byte Alphanumeric String
– Used in Frame Headers
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 Two forms of WLAN
Installations
– Ad-hoc - IBSS
• Equal Peer-to-peer
• No AP
– Infrastructure - BSS
• STAs communicate through APs
• BSS is an area with a single AP
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Wireless Channels
 Channels are created by giving each a part of the RF spectrum
– Each one can carry on a separate conversation (Think of a TV)
– Can be set manually or automatically
 Channels will often overlap frequencies, but conversations cannot overlap
 Newer technologies combine channels into a wider one for better bandwidth
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CSMA/CA
 A WLAN technology designed to
make collisions impossible
 Carrier Sense Multiple Access with
Collision Avoidance (CSMA/CA).
– Reserves a channel for use by a
conversation
– No other devices can transmit on that
channel
 CSMA/CA Reservation Process
– For a Device to use a channel, it asks the
AP by using a Request To Send (RTS)
message.
– If channel is not in use, AP will send Clear
To Send (CTS) message to all devices in
the BSS so they know the channel is
being used.
– Data is sent from STA
– After conversation is done, an
Acknowledgement (ACK) is transmitted.
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Wireless Access Point Configuration
 Integrated wireless access
point
– Network Mode
• 802.11b, g, or a different
technology
– SSID
• Name of your wireless
network
– Standard Channel
• Default is AUTO, but this
decides which channel will be
used
– SSID Broadcast
• Sends out the SSID to the
world
• Default is ENABLE
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Wireless Client Configuration
 Client software allows hardware to
connect to the WLAN.
 For connection to occur, the SSID,
security settings, and channel must
match the AP.
 Wireless Utility Software usually comes
with the NIC
 Some features
– Link Information: strength and quality
of signal
– Profiles: specify configuration options
– Site Survey: checks for all WLANs in
the area
– To use the vendor software, Windows
XP wireless software must be disabled.
 For most purposes, XPs built-in
wireless drivers can be used.
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Wireless LAN Security Issues & Mitigation Strategies
 One large benefit to Wireless networks is also biggest
vulnerability: transmission of information through the air.
 Attacks don’t need physical access to equipment, just be in
range.
– War Driving or Walking to discover insecure networks
 If they gain access, an attacker can:
– Use your Internet for free
– Hack your computers or files
 Special security protocols have been developed to protect
networks, but there are simple steps as well.
– Disable the SSID broadcast so that your network isn’t public.
– Change your default settings
• IP Address
• Router Name
• Admin Password
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Wireless LAN Security - MAC Address Filtering
 Controls exactly which
devices have access to the
LAN
 Uses MAC addresses to ID
clients authorized to access
WLAN.
 Limitations:
– MAC addresses for authorized
clients must be input manually.
– This makes adding new clients
difficult
– MAC Address cloning or
spoofing can allow an
unauthorized user to get into the
WLAN.
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Wireless LAN Security - Authentication
 This process requires a client to
present credentials in order to use
the network.
 Most common is a username and
password, but for a wireless
network, this is handled differently.
 Because the transaction is wireless
and can be “heard” by anyone, the
authentication is done before
connecting.
 Three Types of Authentication:
– Open
• Used for Public Networks
• Networks where another method
of authentication is used.
– PSK
– EAP
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Wireless LAN Security - Authentication
 PSK (Pre-Shared Key)
– Both client and AP are configured with a shared key
– Password is encrypted by client using shared key, then sent to AP, where
it is decrypted using the same key.
– Doesn’t authenticate AP or User, only one way
 EAP (Extensible Authentication Protocol)
– Authentication is 2-way
– Client communicates through AP to (usually) a RADIUS server which has
list of authorized users and clients.
– Both user and client must authenticate.
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Wireless LAN Security – Data Encryption
 Use of Wireless Authentication
– Authentication can prevent unauthorized users from accessing WLAN, but
data is still transmitted to anyone with a receiver.
– Encryptions methods were developed to encrypt wireless communications
to prevent snooping by outsiders.
 Two main encryption methods:
– WEP (Wired Equivalency Protocol)
• Uses pre-configured 64, 128, or 256 bit keys to encrypt data before
transmission.
• WEP keys are just a string of letters or numbers and can also be
automatically generated using a passphrase.
• WEP is not a secure protocol and can easily be cracked by a
knowledgeable wireless hacker.
– WPA (Wi-FI Protected Access)
• Also uses a 64 to 256 encryption key.
• WPA doesn’t always use the same key, but generates new, dynamic
keys each time a client connects.
• WPA is considered the current standard of encryption for wireless
networks.
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Wireless LAN Security – Traffic Filtering
 Allows control of traffic types sent across WLAN
 Blocks undesirable traffic from entering or leaving network
 Filtered using
– MAC Addresses
– IP Addresses
– Port Numbers
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Planning the WLAN
 Planning a WLAN is
important so that the
administrator can
determine
–
–
–
–
Wireless standard
Most Efficient Layout
Installation and Security
Backups for Devices
 Standard Used is Affected by:
–
–
–
–
Number of users
Size of Area Covered
Current Network
Budget
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 Number of users
– WLAN Bandwidth is shared between all
users, so number of clients and APs
matters.
 Size of Area Covered
– Different technology has different areas of
coverage:
– E.g. 2.4 GHz band used in 802.11 b/g/n
has a great radius than the 5Ghz used in
the 802.11a tech.
– Larger BSS
 Budget
– Cost is always a factor
– TCO (Total Cost of Ownership) must be
considered for any installation
– Size needed, existing equipment,
interference of signal, etc. must all be
considered during planning phase.
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WLAN Security Measures
 Security should be
planned and configured
before installing into
network or ISP
 Basic measures:
– Change Defaults for SSID,
usernames, and PWs
– Disable SSID broadcast
– MAC Address Filtering
 Advanced Measures
– WPA or WEP Encryption
– Authentication
– Traffic Filtering
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Backup and Restoring AP Configurations
 Configuration files for APs are
stored in their non-volatile
memory
 Any stored memory can be
corrupted, so it’s important to
backup the configuration in case
of problems.
 Backup
– Save the configuration file to a
secure location
 Restore
– Use the restore button to upload the
file to the AP
 Setting to Factory Default
– Menu option
– Hold RESET button for up to 30
seconds.
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Updating Firmware
 Firmware is a basic OS for the AP or Router stored in flash
memory
 Can be updated using the GUI on the AP/Router
– Download from manufacturer’s website
– Make sure to check version currently being used
 NEVER interrupt an update while it is being uploaded, it may
make the AP/Router unusable.
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Summary
 Wireless technologies use electromagnetic radiation
in the form of radio signals to carry information
between devices.
 Ease and convenience of connecting devices
wirelessly creates security concerns that need to be
addressed.
 Before installing wireless devices, an installation plan
should be created which includes strategies for
layout and security.
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