300-430 · Question #242
An engineer is configuring a wireless LAN controller and is setting these 802.11a/n data rates: 5.5 Mbps - Supported 11 Mbps - Mandatory 24 Mbps - Disabled 56 Mpbs - Supported Which configuration chan
The correct answer is C. Set the 24 Mpbs rates to Mandatory.. On a Cisco WLC, multicast and broadcast frames are transmitted at the highest configured mandatory data rate, so 24 Mbps must be changed from Disabled to Mandatory to use it for multicast.
Question
An engineer is configuring a wireless LAN controller and is setting these 802.11a/n data rates:
5.5 Mbps - Supported 11 Mbps - Mandatory 24 Mbps - Disabled 56 Mpbs - Supported Which configuration change must be made for the multicast broadcast to be sent over 24 Mbps?
Options
- ASet the 24 Mpbs rates to Supported.
- BSet the 56 Mpbs rates to Disable.
- CSet the 24 Mpbs rates to Mandatory.
- DSet all rates to Disable except 11 Mpbs rates.
How the community answered
(20 responses)- A15% (3)
- B5% (1)
- C75% (15)
- D5% (1)
Why each option
On a Cisco WLC, multicast and broadcast frames are transmitted at the highest configured mandatory data rate, so 24 Mbps must be changed from Disabled to Mandatory to use it for multicast.
Setting 24 Mbps to Supported marks it as an optional client rate but does not designate it as a mandatory rate, so multicast frames would still be sent at 11 Mbps - the highest mandatory rate.
Disabling the 56 Mbps rate has no effect on multicast transmission because multicast is driven by the highest mandatory rate, and 56 Mbps is already only Supported, not Mandatory.
Cisco WLC sends multicast and broadcast traffic at the highest mandatory data rate configured on the WLAN. Currently, 11 Mbps is the highest mandatory rate, so multicast is sent at 11 Mbps. Setting 24 Mbps to Mandatory makes it the new highest mandatory rate, which causes the WLC to transmit all multicast and broadcast frames at 24 Mbps. This is a defined behavior of how mandatory rates govern non-unicast frame transmission.
Disabling all rates except 11 Mbps would leave 11 Mbps as the only mandatory rate, causing multicast to be sent at 11 Mbps - not the desired 24 Mbps.
Concept tested: WLC mandatory data rates governing multicast and broadcast transmission
Source: https://www.cisco.com/c/en/us/support/docs/wireless/4400-series-wireless-lan-controllers/107949-configure-data-rates-wlc.html
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