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55 Cards in this Set
- Front
- Back
IEEE standards for wireless
802.3 is for ethernet |
802.11a, 802.11b, 802.11g
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WLANs (wireless LAN)
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uses radio freq instead of cables and MAC sub-layer of the Data Link Layer.
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RF characteristics
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-does not have limitations such as the limits of a wire in a sheath.
-RF is unprotected from outside signals. -RF transmission can have interference from radio -RF bands are regulated differently in different countires. |
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difference between ethernet and wireless
802.3 physical layer - cable media access - collision detection availability - cable connection signal interference - not really regulation - IEEE standards |
802.11
- physical layer - RF media access - collision avoidance availability - radio nic in range of an access point signal interference - yes regulation - depends on the area |
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WLAN connection
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is through Access point instead of an ethernet switch
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data rates for different WLAN standards
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a and g can support 54Mb/s
b supports 11Mb/s 802.11n is not yet set. |
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what affects data rates
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modulation : a way of combining user information with the carrier signal
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modulation types
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DSSS - Direct Sequence Spread Spectrum
OFDM - Orthogonal Frequency Dvision Multiplexing |
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802.11a
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uses OFDM and uses 5GHz band
-less likely to get interferences with devices that operate in 2.4GHz band. -higher frequency allows for smaller antennas. -higher frequency is more succeptible to obstacles such as walls. -smaller range than b or g. |
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802.11b
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uses data rates of 1, 2, 5.5 and 11Mb/s in the 2.4 GHz band using DSSS
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802.11g
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uses OFDM
-gets higher data rates -uses DSSS for backward compatibility -OFDM rates are 6, 9, 12, 18, 24, 48 and 54Mb/s |
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advantages to using the2.4GHz band
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better range than 5GHz.
transmissions are not easily obstructed. |
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802.11n
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uses mutliple radios and antennae at endpoints
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access points
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wireless clients don't talk to each other directly, they go through the AP.
-converts the TCP/IP data packets from their 802.11 frame encapsulation format in the air to the 802.3 ethernet fram format on the wired ethernet network |
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CSMA/CA
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Carrier sense Multiple Access with Collision avoidance.
The devices on a WLAN must sense the medium for energy (RF stimulation above a certain threshold) and wait until the medium is free before sending. |
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data transfer from client to AP
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if an AP receives data from a client, it sens an ack to the client.
-the ack informs the client that the data was successful. |
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The hidden Node problem
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if two devices are at the maximum range to reach the access point and at opposite sides of each other, they cannot sense each other. They might end up transmitting simultaneously.
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RTS/CTS
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-request to send/clear to send
-to solve the hidden node proble -negotiate between client and AP. -access points allocate the medium to the requesting station for as long is required to complete the transmission. When the request is complete, other clients can request the channel. |
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wireless router
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performs the role of access point, switch and router.
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wireless network mode
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refers to the protocols, a, b, g and n
when b and g are both used, it's in a mixed mode. |
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SSID
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shared service set identifier
a client uses this to distinguish between multiple wireless networks. |
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channels
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2.4GHz band is broken to 11 channels for North America and 13 for Europe.
-they have a fequency separation of 5MHz and total of 22 MHz channel bandwidth. -separate out access point 5 MHz apart so that they don't overlap |
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Basic service set
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is a group of stations that communicate with each other.
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IBSS
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independent basic service set
-ad hoc networks without access points |
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ESS
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extended service sets
-when one BSS doesn't have enough RF coverage, one or more can be joined thorugh ESS. A BSS is identified by the BSSID which is the MAC address of the AP. |
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Beacons
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framed used by the WLAN network to advertise its presence
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probes
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frames used by the WLAN clients to find their networks.
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authentication
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a process left over from the original 802.11 standard.
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Association
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process of establishing the data link between an access point and a WLAN client.
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802.11 join process
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-client searches for a network by sending out a probe request on multiple channels
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Beacons
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framed used by the WLAN network to advertise its presence
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probes
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frames used by the WLAN clients to find their networks.
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authentication
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a process left over from the original 802.11 standard.
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Association
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process of establishing the data link between an access point and a WLAN client.
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802.11 join process
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-client searches for a network by sending out a probe request on multiple channels
-probe request has the SSID and bit rates. |
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802.11 join process step2
authentication |
-WEP key that is shared between client and AP.
-clients sends an authentication request, AP sends a challenge test to the client. -client sends the shared key in an encrypted text back to the AP. -AP validates the key. |
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step 3
association |
-finalizes the security and bit rate options
-establishes the link between WLAN client and the AP. -client learns the BSSID, which is the AP's MAC, -access point maps a logical port know as association id to the client. |
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802.11 join process step2
authentication |
-WEP key that is shared between client and AP.
-clients sends an authentication request, AP sends a challenge test to the client. -client sends the shared key in an encrypted text back to the AP. -AP validates the key. |
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step 3
association |
-finalizes the security and bit rate options
-establishes the link between WLAN client and the AP. -client learns the BSSID, which is the AP's MAC, -access point maps a logical port know as association id to the client. |
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war drivers
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find open networks and use them for internet access
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hackers
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exploit weak privacy measures to view sensitive WLAN information and even break into WLANs
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employees
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plug APs or gateways to company ports to create their own WLANs
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rogue AP
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is placed on aWLAN to interfere with normal network operation.
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man in the middle attacks
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select a host as a target and position themselves between the target and the router or gateway.
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Dos
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using a PC as an access point, can flood the BSS with clear to send messages. The acces spoints in tern can flood the BSS with simultaneous traffic.
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authentiation
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SSID - no encryption, basic authentication,
WEP - no strong encryption, static breakable keys WPA - standardized and improved encryption, strong user based authentication. WPA2 - AES encryption authentication. Dynamic key management. |
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EAP
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extensible authentication protocol
framework fo authenticating network access. |
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EAP process
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802.11 association creates a virtual port for each WLAn client
-AP blocks all data frames except for 802.1x based traffic -802.1x carry the EAP authentication packets via access point to the server that maintains the credentials. -if authentication is successful, the serves sends a EAP success message to the AP. |
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TKIP (Temporal Key Integrity Key)
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encryption mechanism
-encrypts by adding increasingly complex bit coding to each packet -based on same cipher as WEP. -carries out a message integrity check in the encrypted packet. |
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AES (Advanced Encryption standard)
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-based on tKIP with additional features to enhance the level of provided security
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SSID cloaking
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disable SSID broadcasts from teh access points
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MAC address filtering
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tables are manually constructed on the access point to allow or disallow clients based on their physical hardware address
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WLAN security implementation
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WPA or WPA2
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configure a wireless access point
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1. verify local wired operation (DHCP and Internet access)
2. Install the access point 3. configure the access point - SSID 4. instaall one wireless client 5. vierfy network operation 6. configure wireless security 7. verify wireless network operation. |
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basic wireless settings
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network mode
network name or SSID SSID broadcast Radio band wide channel standard cahnnel |