Question 49 of 240 from exam 400-351: CCIE Wireless Written Exam

Question 49 of 240 from exam 400-351: CCIE Wireless Written Exam


You are designing a wireless infrastructure for an enterprise customer in the busy international banking district of Tokyo.

All the client adapters are fairly modern, so you have turned off 802.11b speeds to reduce the size of your cells.

Which channels will you choose to make optimum use of the available spectrum?



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A. B. C. D. E.


When designing a wireless infrastructure, one of the important considerations is the selection of the right set of channels to minimize interference and maximize the available bandwidth. In the given scenario, since the client adapters are modern, we can turn off the legacy 802.11b speeds which will allow us to use wider channels for faster data rates.

Out of the given options, the most appropriate choice for the channels would be Option B: 1, 6, 11. The reasons for this choice are as follows:

  1. Channel Overlapping: Wi-Fi channels can overlap with each other, causing interference and reduced performance. The 2.4 GHz band used by 802.11b/g/n has only three non-overlapping channels (1, 6, and 11), while the 5 GHz band used by 802.11a/n/ac has many more non-overlapping channels. Option B uses these non-overlapping channels (1, 6, and 11) to ensure that the access points don't interfere with each other.

  2. Maximum bandwidth: Modern wireless networks use wider channels to increase the data rates. In the 2.4 GHz band, using channels 1, 6, and 11 allows for the use of 20 MHz wide channels. Wider channels (such as 40 MHz) can be used in the 5 GHz band. Option B is the only choice that uses the non-overlapping channels, allowing us to use 20 MHz channels.

  3. Regulatory restrictions: The use of wireless frequencies is regulated by national regulatory authorities. The allowable channels may vary depending on the country/region. In Japan, for example, the use of channel 14 is not allowed. Option C includes channel 14, which is not allowed in Japan, and should be avoided.

  4. Other options: Option A uses channels 1, 5, 9, and 13, which can cause overlapping and interference. Option D uses channels that are not non-overlapping and can cause interference. Option E uses channels 1, 5, and 9, which again can cause interference and do not use the non-overlapping channels.

In conclusion, the best choice of channels for the given scenario is Option B: 1, 6, 11, as it allows for maximum bandwidth, avoids regulatory restrictions, and minimizes channel overlapping and interference.