wireless lan presented by: damian borth, florian seidel, thomas winterscheid
TRANSCRIPT
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Wireless LAN
presented by:
Damian Borth, Florian Seidel,
Thomas Winterscheid
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Contents
Definition The IEEE 802.11 standards Infrastructure and Impairments Hardware System Providers Advantages and Disadvantages Security Alternatives
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Table of content
IEEE Standard 802.11 Basics
FrequencyOSI / ISO LayerModulationNet topology
Properties
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Standard
There is the IEEE 802.11 Standard for WLAN`s
Sub specifications802.11a802.11b802.11g802.11e
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Basics
OSI / ISO overviewPhysical Layer
• Wireless LAN is almost exclusively Spread Spectrum Radio
• direct sequence spread spectrum (DSSS)• frequency-hopping spread spectrum (FHSS) • infrared pulse position modulation (IrDA)
Data Link Layer• Carrier Sense Multiple Access with
Collision Avoidance (CSMA/CA) protocol
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Basics
Frequence ISM band 2.4 GHz and 5 GHz 2.4 - 2.4835 GHz frequency band 5.725 - 5.850 GHz frequency band
Modus Ad hoc mode
• Peer to peer
Infrastructure mode• Using an access point network
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Properties
Range: 100m – 400m (outdoors) 802.11b- DSSS @11Mbps 2.4GHz 802.11a- DSSS @54Mbps 5GHz 802.11g- DSSS @22Mbps 2.4GHz 802.11e- DSSS @22Mbps w/QoS
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Contents (Part 2)
Definition The IEEE 802.11 standards Infrastructure and Impairments Hardware System Providers Advantages and Disadvantages Security Alternatives
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How to install?
Two different use modes:AdHoc (P2P)Infrastructured (LAN) ?
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?
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Adhoc
Standard P2P connection Only for two PC`s Same way of configuration (IP range
etc...) Transferrate 11 Mbit/s Range ca. 30m-50m (outdoor 400m) WEP against eavesdropping
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Infrastructured
Access points are needed Range 30m - 50m Access points act like bridges/gateways Installation of access points enables
„Roaming“ functionality Configuration of IP and administration like in
wired network Transferrate 11 Mbit/s
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Impairments
Weakened by solid walls and concrete No influence through glass Range impairment can be increased
with additional antenna up to 2 km Bluetooth / IrDA
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Which hardware you need?
WirelessLan-Card
Adapter USB
Access Point
e.g. Fujitsu-Siemense.g. Fujitsu-Siemens I-Gate WLANI-Gate WLAN
Pre-installed
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Wired?
Connectivity to wired LAN Access points must be installed
(bridge functionality) Connectable to each kind of LAN
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Roaming
Extended connectivity possibility Allows free mobility Access points transfers given IP within the network Roaming between different networks is also
possible (bridge/gateway)
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Access to WAN?
...is possible by using access points connected to ISDN / DSL
Access points can act like a gateway No impairment to the transferrates
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System provider
Producer Fujitsu-Siemens Aironet NDC Proxim Bay Networks Lucent RDC
Productname I-Gate Telxon Serie 3500 Instantwave Rangelan Airsurfer Wavelan Portlan
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Contents (Part 3)
Definition The IEEE 802.11 standards Infrastructure and Impairments Hardware System Providers Advantages and Disadvantages Security Alternatives
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Advantages
mobility / flexibility inexpensiveness ease of installation / usage extends LAN and doesn’t need to
replace it
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Disadvantages
lack of security lower transmission rates than in wired
networks
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Security
basic problem: broadcast of radio data transmission
piracy tools: AirSnort WEPcrack Network Stumbler, etc.
real problem: default settings of WLAN are insecure, e.g. „Accept ANY SSID“
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Security - WEP
Wireless Equivalent Privacy based on RC4 encryption algorithm most important, but optional 128 bit encryption algorithm for data
encryption and authentification
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Security - WEP
WEP does stream-encryption + generates key for each data package
to set up the stream, WEP uses the shared key and an initialization vector
the plain text information is parsed bit-by-bit and combined with pseudo random numbers (ensures that packages with same content are not equally encrypted)
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Security - WEP
a carrier frequency is determined by the constallation of the data stream and broadcasted throughout the WLAN
the recipient deletes the pseudo random numbers and restores the plain text information
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Weak Point
Initialization Vector (IV)24 biteasily predictable (usually increment
by1)Same IV + (constant) Shared Key
IV-Collision (same WEP-Key)many IV-Collisions allow extraction
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Security check
change default settings (e.g. password)
use WEP encryption change WEP key regularly filter MAC addresses position APs before firewall
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Security check
check log files for intrusion attempts use “intrusion detection system” turn off DHCP use authentification
for extra high security use a VPN.
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References & Bibliography
http://www.ieee.org http://www.tecchannel.de http://www.fujitsu-siemens.de “Data and Computer
Communications”,Sixth Edition, William Stallings, Prentice Hall
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Any Questions?
Thank you.