Chapter 7 Flashcards
Wardriving
Type of wireless reconnaissance with special-purpose software tools to enable you to learn more about the WLANs you discover with the intent on helping you to break into them
IEEE 802.3
IEEE standard for wired Ethernet
IEEE 802.11
IEEE standard for wireless Ethernet
Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
Contention-based media access control technique which waits until the circuit is free and then transmits.
The solution to a collision would be to listen while you transmit (collision detection). If the NIC detects any signal other than its own, it presumes that a collision has occurred and sends a jamming signal. All computers stop transmitting and wait for the circuit to become free (random time) before trying to retransmit.
Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)
Computers listen before they transmit, if no one else is transmitting, they proceed with transmission.
2 approaches - Distributed Coordination Function (physical carrier sense method) and Point Coordination Function (virtual carrier sense method)
- Distributed Coordination Function - Each frame in CSMA/CA is sent using stop-and-wait ARQ. After the sender transmits one frame, it immediately stops and waits for an ACK from the receiver before attempting to send another frame.
- Point Coordination Function - Any computer wishing to transmit first sends a request to send (RTS) to the AP. The RTS requests permission to transmit and to reserve the circuit for the sole use of the requesting computer for a specified time period. If no other computer is transmitting, the AP responds with a clear to send (CTS), specifying the amount of time for which the circuit is reserved for the requesting computer.
100Base-T
100Base-F
1000Base-F
100 - speed 100MB per second
Base - baseband. can only have 1 signal in network at a time
T/F - type of medium. Twisted pair or fiber optic
Logical topology
How the network works conceptually
Physical topology
How the network is physically installed
Hub-based Ethernet
Logical topology is a bus topology but a physical star topology
All computers are connected to one half-duplex circuit running the length of the network called a bus. Every computer on the bus receives all frames sent on the bus, even those intended for other computers. Before processing incoming frames, the Ethernet software on each computer checks the data link layer address and processes only those frames addressed to that computer.
Switched-based Ethernet
Topology is a logical star and a physical star.
When a switch receives a frame from a computer, it looks at the address on the frame and retransmits the frame only on the circuit connected to that computer, not to all circuits as a hub would. Therefore, no computer needs to wait because another computer is transmitting; every computer can transmit at the same time, resulting in faster performance, as a result, each port on the switch is in a separate collision domain, and there are only two devices on it: the switch and the computer/device on the other end of the cable.
Components of a LAN
Client computer, server, switch, access point, network interface card
Service Set Identifier (SSID)
The name for the WiFi network
Wired Equivalent Privacy (WEP)
With WEP, the AP requires the user to have a key to communicate with it. All data sent to and from the AP are encrypted so that they can only be understood by computers or devices that have the key.
WiFi Protected Access (WPA)
Works in ways similar to WEP: every frame is encrypted using a key, and the key can be fixed in the AP or can be assigned dynamically as users login. The WPA key is longer than the WEP key and thus is harder to break. The key is also changed for every frame that is transmitted to the client.
802.11i (WPA2)
Newest and most secure type of security. The user logs in to a login server to obtain the master key. Armed with the master key, the users computer and AP negotiate a new key that will be used for this session until the user leaves the WLAN.
