How Do Eight WLCs Reduce Mobility Group Bandwidth?
An engineer has eight WLCs in a mobility group and must reduce the bandwidth consumed. Which two configuration items achieve this result? (Choose two.)
Community Votes
100% of anonymous learners picked answer AD. Votes are pick records left by other test-takers — they are not the verified answer.
Community Insight
It tests the two multicast-based settings that shrink replication in a large mobility group, and the trap is picking an option containing 'unicast' because it sounds more efficient when it actually multiplies traffic.
With eight WLCs in one mobility group, bandwidth is consumed twice: by replication of data toward APs and by controller-to-controller mobility messaging. This page establishes that global multicast mode plus mobility group multicast messaging are the two settings that cut that traffic (A, D).
Selecting mobility group unicast messaging (B), because with only a handful of controllers unicast feels direct and lightweight; in an eight-WLC group each controller must unicast to every peer, so traffic and CPU load grow instead of shrink.
Community Discussion (3 comments)
Comments & Corrections
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Expert Analysis
Why the Answer Is Correct
Global multicast mode (A) changes how the WLC forwards a data stream: instead of replicating one unicast copy per subscribed AP, the controller sends a single copy to a multicast group address and the APs that joined that group receive it. That removes the per-AP duplication that dominates bandwidth on a large deployment. Mobility group multicast messaging (D) applies the same principle to inter-controller traffic: the eight members of the mobility group exchange mobility messages over a multicast group address rather than each controller unicasting separately to the other seven. Together they address the two places where an eight-WLC design wastes bandwidth, which is exactly what the question asks for. One community member summarized the sequence simply, noting that you "need first to enable multicast. then enable mutlicast on the mobility group", which matches the ordering of A before D. Another learner pointed out that A sends "only a single copy of multicast data to the multicast group address instead of sending one copy to each and every subscribed AP," which is the core bandwidth-saving mechanism being tested. Enabling both is also why the exam expects two answers, not one.
Why the Other Options Are Wrong
Mobility group unicast messaging (B) is the default behavior in a mobility group, so selecting it would leave bandwidth exactly as it is; with eight WLCs it means each controller maintains unicast conversations with seven peers, which is more traffic than one multicast stream. Global unicast messaging (C) is not a bandwidth-reducing WLC setting at all, since normal client unicast delivery is already point-to-point and this option does not describe any multicast offload. As one commenter noted, "Mobility group unicast messaging increases bandwidth usage," so it is the opposite of what the scenario requires. Global symmetric mobility messaging (E) is a fabricated-sounding option: mobility tunneling between controllers in a group is inherently symmetric, so there is no such global knob that trims bandwidth.
Community Comment Notes
All three visible comments converge on AD, and the reasoning is consistent with the vendor behavior rather than simple vote-following. The first explains the two-step order (global multicast first, then mobility group multicast). rrahim frames A as optimizing traffic by replacing multiple unicast packets with a single multicast stream and D as making the WLCs exchange mobility information efficiently, while explicitly calling out unicast messaging as the wrong turn. The third reinforces A by describing one copy going to the group address instead of one copy per AP. No comment disputes AD, and none proposes a different pairing, so the community record supports the same conclusion reached from the configuration logic.
Exam Strategy
When a 300-430 question mentions many controllers or APs plus the words 'reduce bandwidth', scan the options for the two multicast-based settings and treat every 'unicast messaging' option as a distractor. Remember the ordering dependency: multicast mode is enabled globally first, then applied to the mobility group, which is how you confirm both letters belong together.
Frequently Asked Questions
Does mobility group multicast messaging work without global multicast mode?
No. Multicast must be enabled globally on the WLC first; the mobility group multicast setting then uses that multicast transport to reach the peer controllers.
Why does mobility group unicast messaging waste bandwidth with eight WLCs?
Each controller unicasts mobility messages to all seven peers, so replication and control-plane load grow with group size instead of being carried in one multicast stream.