Computer Networks

1. Computer Networks

2. Network Connections • Ethernet Networks • 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

3. Ethernet Networks • Rules or Protocols • One computer does not interfere with communications by another • Each computer ‘listens’ to the network as it transmits it message • 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

4. 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 • Cabling limited to 100 meters (328 feet) • Hubs - A common connection point • Repeaters – amplify electrical signals

5. Wireless Technology • Wireless communications • Infrared signals or radio waves • Devices on a wireless network form a logical Ethernet network • Messages are divided into packets • Packet contains a header • 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

6. 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

7. 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

8. 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.

9. WLAN Security • SSID • 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 • MAC: hardware/physical address of wireless network card • Only allow specified MAC addresses for connections

10. WLAN Security • WEP: Wired Equivalent Privacy • WPA: Wi-Fi Protected Access • WPA2: Best protection for home WLAN.

11. WEP: Wired Equivalent Privacy • Purpose: • Protect wireless network from eavesdropping. • Prevent unauthorized access to the network • How Does It Work • A secret key between laptop and access point • The secret key to encrypt packets • Length of Key • 64-bit encryption • 128-bit encryption

12. 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 • Extra-strong encryption • Encryption keys are automatically changed • after a specified period of time • after a specified number of packets • Implements a subset of IEEE 802.11i.

13. WPA2: Wi-Fi Protected Access • WPA2: Best protection for home WLAN. • 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.