Computer Networks
Network Connections
 Ethernet Networks
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Single wire (or bus) runs to all machines
Any computer can send info to another
computer
Header – intended recipient
All computers receive all communications,
however only intended computer saves
material
Ethernet Networks
 Rules or Protocols
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One computer does not interfere with
communications by another
Each computer ‘listens’ to the network as it
transmits it message
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If the message received is different, another
computer sent message at same time
Wait random amount of time and resend
Maximum length for any message
Expansion of networks
 Variations in degree to which
networks are used
 To keep demand low on networks,
many organizations maintain
separate small networks and connect
those networks
 Ethernet networks
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Cabling limited to 100 meters (328
feet)
Hubs - A common connection point
Repeaters – amplify electrical signals
Wireless Technology
 Wireless communications
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Infrared signals or radio waves
Devices on a wireless network form a logical
Ethernet network
Messages are divided into packets
Packet contains a header
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IDs which machine is to receive the data
All wireless computers in an area share the
airwaves, receive the same messages and
determine if they are the recipient
Wireless Technology
 Access Point
 Computer directly to the Internet (acts as intermediary)
 Example: on a 2.4 GHz radio frequency band
 Beacon
 Repeating of identifying information by access point
 Association – Portable wishes to make connection
 Portable computers use radio waves or infrared
signals to communicate with access point
 As portable computers move, interact with new
access point
 If no computers have direct access to the Internet,
portable computers still can interact with each other,
but not with the Internet
Types of Wireless Network Attacks - 1
 Insertion attacks: When a wireless device
connects to an access point without
authorization
 Interception /monitoring of wireless traffic:
The network traffic across a WLAN is
intercepted and monitored without
authorization.
 Mis-configuration: Many access points ship
in an unsecured configuration
Types of Wireless Network Attacks - 2
 Client-to-client attacks: Two wireless clients
can communicate with each other directly.
One may attack another.
 Jamming: DoS (Denial of Service) legitimate
traffic overwhelms the frequencies, making
the network not usable.
WLAN Security
 SSID
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Service Set Identifier or Network Name
Name of a wireless local area network
All wireless devices on a WLAN must employ
the same SSID
NOT broadcast SSID in access points
 MAC Filtering
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MAC: hardware/physical address of wireless
network card
Only allow specified MAC addresses for
connections
WLAN Security
 WEP: Wired Equivalent Privacy
 WPA: Wi-Fi Protected Access
 WPA2: Best protection for home WLAN.
WEP: Wired Equivalent Privacy
 Purpose:
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Protect wireless network from eavesdropping.
Prevent unauthorized access to the network
 How Does It Work
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A secret key between laptop and access point
The secret key to encrypt packets
 Length of Key
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64-bit encryption
128-bit encryption
WPA: Wi-Fi Protected Access
 Two types of WPA
 WPA-PSK (WPA Personal) - Home &Small Offices
 WPA-RADIUS (WPA Enterprise) – Large Organizations
 WPA-PSK: Pre-Shared Key
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Extra-strong encryption
Encryption keys are automatically changed
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after a specified period of time
after a specified number of packets
 Implements a subset of IEEE 802.11i.
WPA2: Wi-Fi Protected Access
 WPA2: Best protection for home WLAN.
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Fully compatible with IEEE 802.11i security
standard.
Stronger encryption protocol
Not all wireless cards and access points support
WPA2 certification is mandatory for all new
devices wishing to be Wi-Fi certified.