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300-370 · Question #23

A Wireless LAN Cisco engineer is troubleshooting 802. 11ac WLAN at customer site Doe to interferences with neighboring 802 11n networks the engineer must determine the current primary secondary…

The correct answer is A. primary 40 MHz channel 62, primary 80 MM: channel 58. Given primary 20 MHz channel 60, the resulting primary 40 MHz channel is 62, and the primary 80 MHz channel is 58, following 802.11ac channel bonding rules for the 5 GHz band.

Troubleshooting WLAN Performance Issues

Question

A Wireless LAN Cisco engineer is troubleshooting 802. 11ac WLAN at customer site Doe to interferences with neighboring 802 11n networks the engineer must determine the current primary secondary channel allocation to enhance the current configuration. Channel 60 has been chosen by the customer as primary 20 MHz channel. Which combination determines the resulting primary 40 MHz and primary 80 MHZ channels?

Options

  • Aprimary 40 MHz channel 62, primary 80 MM: channel 58
  • Bprimary 40 MHz channel 54, primary 80 MHz channel 58
  • Cprimary 40 MHz channel 64, primary 80 MHz channel 60
  • Dprimary 40 MHz channel 60, primary 80 MHz channel 56

How the community answered

(41 responses)
  • A
    73% (30)
  • B
    7% (3)
  • C
    15% (6)
  • D
    5% (2)

Why each option

Given primary 20 MHz channel 60, the resulting primary 40 MHz channel is 62, and the primary 80 MHz channel is 58, following 802.11ac channel bonding rules for the 5 GHz band.

Aprimary 40 MHz channel 62, primary 80 MM: channel 58Correct

For 802.11ac in the 5 GHz band, if channel 60 is the primary 20 MHz channel, it typically pairs with channel 64 to form the 40 MHz channel 62 (center frequency). This 40 MHz block (channels 60 and 64) is then part of the larger 80 MHz channel 58, which encompasses channels 52, 56, 60, and 64, with 58 being the center frequency.

Bprimary 40 MHz channel 54, primary 80 MHz channel 58

If channel 60 is the primary 20 MHz, then channel 54 (channels 52-56) cannot be the primary 40 MHz channel, as it does not include channel 60.

Cprimary 40 MHz channel 64, primary 80 MHz channel 60

If channel 60 is the primary 20 MHz, then 64 is a secondary 20 MHz channel within a 40 MHz block, not the primary 40 MHz channel itself. Channel 60 is a 20 MHz channel, not an 80 MHz channel.

Dprimary 40 MHz channel 60, primary 80 MHz channel 56

If channel 60 is the primary 20 MHz, it cannot also be the primary 40 MHz channel. Additionally, channel 56 is not the correct center for an 80 MHz block that includes channel 60.

Concept tested: 802.11ac channel bonding and primary/secondary channels

Source: https://www.cisco.com/c/en/us/td/docs/wireless/controller/8-5/config-guide/b_cg85/channels.html

Topics

#802.11ac channels#Channel bonding#DFS channels#WLAN RF planning

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