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780 Appendix • Self Test Appendix

Answer B is correct. By far the most devastating attack against WEP is the Fluhrer-Mantin-
Shamir attack of statistically determining the WEP key.This allows an attacker to crack a WEP
key within hours and thereby gain full access to the wireless network or to the traffic on it.
Answer A is incorrect.While the reuse of IV values does provide a significant problem (and in
fact leads to the success, in some cases, of the Fluhrer-Mantin-Shamir attack) it is not as great a
threat as FMS.Answer C is incorrect.The capability to spoof MAC addresses is not a problem
with WEP, but rather with 802.11 as a whole.Answer D is incorrect.

6. The tool NetStumbler detects wireless networks based on what feature?
A. SSID
B. WEP key
C. MAC address
D. CRC-32 checksum
Answer A is correct. NetStumbler detects wireless networks by looking for SSIDs.Answer B is
incorrect. NetStumbler does identify networks with WEP enabled, but does not use that fact in
identifying the network.Answer C is incorrect. NetStumbler does detect clients and APs based
on their MAC but does not use this information for identifying wireless networks.Answer D is
incorrect because CRC-32 checksums are of no concern to NetStumbler.

7. Some DoS attacks are unintentional.Your wireless network at home has been having sporadic
problems.The wireless network is particularly susceptible in the afternoon and the evenings.
This is most likely due to which of the following possible problems?
A. The AP is flaky and needs to be replaced.
B. Someone is flooding your AP with traffic in a DoS attack.
C. The wireless network is misconfigured.
D. Your cordless phone is using the same frequency as the wireless network and whenever
someone calls or receives a call the phone jams the wireless network.
Answer D is correct.The most likely problem is that a cordless phone (or a microwave or one
of many other wireless devices) is jamming the wireless signal because it uses the same fre-
quency.This is becoming more and more common as cordless phone manufacturers use the 2.4
GHz frequency.Answer A may be possible, but should not be considered seriously until other
sources of the problem are ruled out.Answer B is possible but unlikely.Answer C is incorrect
because misconfiguration of the wireless network would probably result in the problem occur-
ring at all times, rather than just in the afternoon or evenings.

8. The 802.1x standard requires the use of an authentication server to allow access to the wire-
less LAN.You are deploying a wireless network and will use EAP-TLS as your authentication
method.What is the most likely vulnerability in your network?

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