Wireless Networks

Question 1

Wireless Access Point

Answer 1

Expands wired LAN into wireless domain
Does NOT interconnect two networks
Functions as a hub

Connects wired LAN & wireless devices into the same subnet

All clients on an access point are on a single collision domain

Question 2

IBSS

Answer 2

Independent Basic Service Set
Contains only devices/clients with no APs
(Ad-hoc WLAN)

Question 3

BSS

Answer 3

Basic Service Set
Only one AP connected to the network
(SOHO network)

Question 4

ESS

Answer 4

Extended Service Set
Contains multiple APs to provide coverage
(College campus)

Question 5

Mesh Topology

Answer 5

May not use a centralized control
Range of combined wireless defines network
Uses Wifi, Microwave, Cellular, & more

Question 6

AP Placement (2.4GHz)

Answer 6

Non-overlapping coverage cells for 2.4GHz band should have 10-15% coverage overlap in coverage area

Question 7

AP Placement (5GHz)

Answer 7

Identical channels should be separated by at least two cells instead of one

Question 8

Site Surveys

Answer 8

Wireless survey to determine coverage areas

Produces a heat map with coverage

Question 9

Wireless Range Extenders

Answer 9

Specialized device that overcomes distance limitations of wireless networks

Amplifies the signal & extends reachability of a wireless cell

Wireless repeater receives signal on one antenna & repeats on the other

Question 10

RFI

Answer 10

Radio Frequency Interference
Caused by using similar frequencies to WLAN

Common sources:
Other Wifi devices, Baby monitors, Microwave ovens, Wireless security systems, appliances/walls/cabinets, signal strength

Question 11

CSMA/CA

Answer 11

Carrier Sense Multiple Access/Collision Avoidance
WLAN uses CSMA/CA, ethernet uses CSMA/CD

Listens for transmission to determine if safe to transmit
If clear, sends RTS (request to send) & waits
If received an RTS, responds with CTS (clear to send)
If not receive, device starts random back off timer

Question 12

Pre-Shared Key

Answer 12

Both AP & client use the same encryption key

Scalability is difficult if key is compromised
All clients must know the same password

Question 13

WEP

Answer 13

Wired Equivalent Privacy
Original 802.11 wireless security standard

Static 40-bit pre-shared key
(Upgraded to 64-bit, and then 128-bit over time)

24-bit IV (Initialization Vector) - Sent in clear text
Very insecure, easily brute forced

Question 14

WPA

Answer 14

Wi-Fi Protected Access
Replaced WEP & its weaknesses

TKIP (Temporal Key Integrity Protocol)
48-bit IV, RC4 (Rivest Cipher 4) encryption

Uses MIC (Message Integrity Check)

Enterprise Mode
Users can be required to authenticate before key exchange
Keys between AP & client are temporary

Question 15

WPA2

Answer 15

Wi-Fi Protected Access 2
Part of 802.11i standard
Requires stronger encryption and integrity checks

CCMP integrity check
AES 128-bit Encryption (Advanced Encryption Standard)

Two modes
Personal - Pre-shared keys
Enterprise - Centralized authentication

Question 16

Captive Portals

Answer 16

Web page that appears before user is able to access the network resources

Webpage accepts user credentials & presents them to authentication server

Question 17

Geofencing

Answer 17

GPS or RFID defines real-world boundaries
Barriers can be active or passive
Device can send alerts if it leaves area
Network authentication can use it to determine access

Question 18

War Driving

Answer 18

Occurs when users perform reconnaissance looking for unsecured wireless networks

Question 19

War Chalking

Answer 19

Occurs when users write symbols on a wall to notify others of AP characteristics

Question 20

Remember that they’re related to wireless networking:

DSSS, FHSS, OFDM

Answer 20

DSSS: Direct-Sequence Spread Spectrum
FHSS: Frequency-Hopping Spread Spectrum
OFDM: Orthogonal Frequency Division Multiplexing