Network+ 10 Flashcards
All wireless devices associating with a single AP share a collision domain.
To manage multiple APs, a company will use a wireless LAN controller (WLC) for centralized management and control of the APs. Using a WLC, VLAN pooling can be used to assign IP addresses to wireless clients from a pool of IP subnets and their associated VLANs.
Omnidirectional = all directions, unidirectional = one direction reach greater distance less interference.
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WLANs use a similar technology called carrier-sense multiple access/collision avoidance (CSMA/CA) is half-duplex, a WLAN device listens for a transmission on a wireless channel to determine whether it is safe to transmit. In addition, the collision-avoidance part of the CSMA/CA algorithm causes wireless devices to wait for a random back-off time before transmitting.
WLANS etc …
Direct-sequence spread spectrum (DSSS): Modulates data over an entire range of frequencies using a series of symbols called chips. A chip is shorter in duration than a bit, meaning that chips are transmitted at a higher rate than the actual data. These chips encode not only the data to be transmitted, but also what appears to be random data.
DSSS
Frequency-hopping spread spectrum (FHSS): Allows the participants in a communication to hop between predetermined frequencies. Security is enhanced because the participants can predict the next frequency to be used, but a third party cannot easily predict the next frequency. FHSS can also provision extra bandwidth by simultaneously using more than one frequency.
FHSS
OFDM uses a relatively slow modulation rate for symbols. This slower modulation rate, combined with the simultaneous transmission of data over 52 data streams, helps OFDM support high data rates while resisting interference between the various data streams.
OFDM
- 11 = 2.4 GHz, 1-2 Mbps, DSSS or FHSS, max range : 20m indoors, 100m outdoors
- 11a = 5GHz, 54 Mbps, OFDM, max range : 35 m indoors, 120m outdoors
- 11b = 2.4 GHz, 11 Mbps, DSSS, 35m indoors and 120m outdoors
- 11g = 2.4 GHz, 54 Mbps, OFDM or DSSS, 38m indoors and 140m outdoors
- 11n = 2.4GHz or 5 GHz, >300 Mbps (with channel bonding), OFDM, 70m indoors and 250m outdoors
- 11ac = 5 GHz, >3 Gbps, OFDM, similar range to 802.11n
802.11 Channels
IBSS : WLAN can be created without the use of an AP. Such a configuration, called an IBSS, is said to work in an ad hoc fashion.
BSS : WLANs that have just one AP are called BSS WLANs. BSS WLANs are said to run in infrastructure mode because wireless clients connect to an AP, which is typically connected to a wired network infrastructure.
ESS : WLANs containing more than one AP are called ESS WLANs. Like BSS WLANs, ESS WLANs operate in infrastructure mode. When you have more than one AP, take care to prevent one AP from interfering with another.
IBSS/BSS/ESS
war driving, where potentially malicious users drive around looking for unsecured WLANs.
War chalking: Once an open WLAN (or a WLAN whose SSID and authentication credentials are known) is found in a public place, a user might write a symbol on a wall (or some other nearby structure) to let others know the characteristics of the discovered network.
Threats
IEEE 802.1x is a technology that allows wireless clients to authenticate with an authentication server—typically, a Remote Authentication Dial-In User Service (RADIUS) server for security.
WEP : specifies a 40-bit WEP key, RC4 uses a 24-bit initialization vector (IV) - transmitted in clear text.
WPA : uses a 48-bit IV. TKIP uses Rivest Cipher 4 (RC4) for the encryption algorithm.
The availability of a network increases as the mean time to repair (MTTR) of the network devices decreases and as the mean time between failures (MTBF) increases.
Wireless Encryption Forms etc …
Active-active: Both NICs are active at the same time, and each has its own MAC address. This makes troubleshooting more complex, while giving you slightly better performance than the active-standby approach.
Active-standby: Only one NIC is active at a time. This approach allows the client to appear to have a single MAC address and IP address, even in the event of a NIC failure.
A computer cluster consists of a set of tightly connected computers that work together.
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