How to Implement Reliable Multicast on AireOS WLC?
An engineer must implement multicast on an AireOS WLC v8.2 that has 200 LWAPs connected. Reliable reception is a main requirement of this implementation. Which wireless configuration must be performed?
Community Votes
67% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.
Community Insight
Tested: multicast transmission uses the lowest mandatory data rate; the trap is confusing coverage cell or higher rate disabling as a fix, when actually disabling the low mandatory rates (1, 2, 5.5, 11 Mbps) forces higher-rate multicast and better reliability.
To implement reliable multicast on an AireOS WLC with 200 LWAPs, you must disable lower mandatory data rates so multicast frames are sent at higher rates, reducing airtime and improving reception. This page confirms option D as the correct configuration and explains why coverage cell adjustments and other rate settings are incorrect.
Many choose C (disable higher mandatory data rates), thinking that removing high rates forces more robust low-rate multicast, but that actually increases airtime and worsens reliability; the correct approach is to disable the low mandatory rates (D).
Community Discussion (3 comments)
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Expert Analysis
Why the Answer Is Correct
The question asks for the wireless configuration needed to ensure reliable multicast reception on an AireOS WLC with 200 LWAPs. In 802.11 networks, multicast and broadcast frames are transmitted at the lowest mandatory data rate configured on the WLAN. In a large deployment, sending every multicast frame at 1 or 2 Mbps consumes significant airtime, which increases congestion and the likelihood of collisions, ultimately degrading reliability. By disabling the lower mandatory data rates (1, 2, 5.5, and 11 Mbps), the WLC forces multicast traffic to use higher mandatory rates such as 6, 12, or 24 Mbps. This reduces the time each frame occupies the channel, lowering overall airtime and improving the probability of successful reception across all 200 APs. Therefore, option D is the correct configuration to meet the reliable reception requirement.Why the Other Options Are Wrong
Option A (increase the coverage cell) and Option B (decrease the coverage cell) relate to the Multicast Direct feature, which is a separate optimization that converts multicast to unicast. The question does not mention Multicast Direct, and even there, coverage cell adjustments alone do not address the fundamental multicast rate issue. Option C (disable higher mandatory data rates) is the opposite of the correct approach: it would remove faster rates, causing multicast to be sent at even lower speeds, increasing airtime and worsening reliability. The only configuration that directly improves multicast reliability by raising the transmission rate is disabling the lower mandatory data rates, so D stands out.Community Comment Notes
Community consensus strongly supports option D, with 67 votes versus 33 for C. As rrahim explains, disabling lower mandatory data rates "multicast traffic is transmitted at higher rates, reducing airtime consumption" and prevents packets from being sent at the lowest basic rate in a 200-AP deployment. Another comment by rrahim reinforces that multicast is sent at the lowest mandatory rate, so removing the slowest rates prevents packets from being sent at 1 Mbps, which is critical in a 200-AP environment. The dissenting comment by 74ca941 simply states "Disable higher mandatory data rates" without explaining why, and that action would actually push multicast to even lower speeds, increasing airtime and reducing reliability.Exam Strategy
In AireOS multicast questions, remember that multicast/broadcast frames are always sent at the lowest mandatory data rate. To improve reliability, the configuration is to disable low mandatory rates (1, 2, 5.5, 11 Mbps) so multicast uses higher rates; don't be tempted by coverage cell options, which apply to Multicast Direct.
Frequently Asked Questions
Why does disabling lower mandatory data rates improve multicast reliability?
Multicast frames are transmitted at the lowest mandatory rate; removing 1, 2, 5.5, and 11 Mbps forces the WLC to use higher rates, reducing airtime and packet loss in large deployments.
Is the coverage cell option relevant for standard AireOS multicast?
Coverage cell is a parameter for Multicast Direct, not basic multicast. For standard multicast, the data rate is determined by the mandatory rate set, so option D is the direct fix.