N10-005 Question #413: Real Exam Question with Answer & Explanation

The correct answer is B: Channel width is set to 40MHz. In the 2.4 GHz band, channels 1, 6, and 11 are the three non-overlapping channels when using standard 20 MHz channel width. Channels 1 and 6 should not interfere with each other at 20 MHz. However, if the channel width is set to 40 MHz (a feature introduced with 802.11n), a 40 MH

Question

A technician has two wireless 802.11g APs. One is set to channel 1 and the other channel 6. The APs appear to interfere with each other. Which of the following is MOST likely the reason?

Options

AChannels below 9 overlap each other
BChannel width is set to 40MHz
CChannels are in the 5GHz range by mistake
DChannel 1 should have been set to 11 to avoid an overlap

Explanation

In the 2.4 GHz band, channels 1, 6, and 11 are the three non-overlapping channels when using standard 20 MHz channel width. Channels 1 and 6 should not interfere with each other at 20 MHz. However, if the channel width is set to 40 MHz (a feature introduced with 802.11n), a 40 MHz channel centered on channel 1 spans approximately channels 1–7, and one centered on channel 6 spans approximately channels 4–10, causing them to overlap and interfere. Setting channel width to 40 MHz on APs in the 2.4 GHz band is the root cause of this unexpected interference.

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