Single 9800-40 WLC High Availability: Multi-LAG Design
Short answer
C Use Multi-LAG on the single Cisco 9800-40 so the WLC dynamically manages port redundancy and transparently balances APs across LAGs to the core switch.
Question
Which design approach must the engineer take to meet the requirements?
Key Takeaways
It tests the distinction between a single LAG or LACP bundle and the 9800 Multi-LAG feature, which manages multiple LAGs and balances APs; the trap is choosing LACP just because the stem says "dynamically."
For a single Cisco 9800-40 WLC that needs cable-failure redundancy and transparent AP load balancing, the correct design is Multi-LAG rather than a plain LAG, LACP, or PAgP.
Common mistake: LACP (B) is a plausible wrong answer because it is the dynamic negotiation protocol, but it only controls member links within one bundle and does not by itself deliver the 9800 Multi-LAG AP-level redundancy and load-balancing design.
Expert Analysis
The budget constraint is the first filter. Because the company can afford only a single Cisco 9800-40 WLC, the design cannot rely on an active/standby controller pair; the high availability has to come from the WLC's connection to the core switch. That immediately shifts attention to link bundling and how the 9800 distributes AP traffic across those links.
The phrase "dynamically manage port redundancy" makes LACP (B) and PAgP (A) tempting. A community comment explicitly seizes on "dynamically" and selects LACP. But a negotiation protocol is not the whole design: LACP only manages member links inside one EtherChannel. It does not, by itself, give the 9800 a mechanism to balance APs across multiple LAGs transparently. PAgP (A) is even weaker here; it is a Cisco-proprietary negotiation protocol and not the 9800 Multi-LAG design called for.
A plain LAG (D) does bundle links and can survive a cable failure, so it passes the first requirement. However, the stem adds two stronger qualifiers: the WLC must dynamically manage port redundancy and perform load balancing between APs transparently. A single LAG load-balances frames across its members; it does not provide the controller-level AP distribution and multi-LAG redundancy described.
Multi-LAG (C) is the design approach that matches all constraints. On a 9800-40 it lets the controller use multiple LAGs, dynamically react to port/cable failure, and transparently balance APs across those LAGs. That satisfies the single-controller budget, the cable-failure HA requirement, and the "dynamically... transparently" wording, so C is the correct answer.
Official Reference
https://www.cisco.com/c/en/us/support/wireless/catalyst-9800-series-wireless-controllers/series.html
This link opens the official vendor documentation in a new tab.
Exam Strategy
On wireless HA questions, separate the protocol from the architecture: LACP/PAgP answer "how links negotiate," while LAG/Multi-LAG answer "what redundancy and load-balancing design is deployed." Read the stem for controller-level outcomes such as AP distribution, transparency, and a single-WLC budget; those point to the 9800 feature, not the protocol. Eliminate any option that only solves one cable's failure when the stem requires dynamic AP balancing.
Frequently Asked Questions
Does a single Cisco 9800-40 support Multi-LAG for WLC-to-switch high availability?
Why is LACP not the best answer when the question says "dynamically"?
What is the difference between LAG and Multi-LAG on a 9800 WLC?
Community Votes
100% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.
Discussion 1 contributions
Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.
From public community threads 1
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leonel591 👍 1 Answered BThe question emphasizes that the WLC must manage redundancy dynamically.
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