How Does a Single 9800-40 WLC Achieve Cable-Failure High Availability?
A network engineer must design a new wireless solution for a company, but the budget can only stretch to include a single Cisco 9800-40 WLC. The company requires high availability between the WLC and the core switch in the event of a cable failure. The WLC must dynamically manage port redundancy and perform load balancing between APs transparently. Which design approach must the engineer take to meet the requirements?
Community Votes
100% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.
Community Insight
Tests WLC port redundancy and AP load balancing design; the trap is picking LACP or PAgP because Cisco 9800 LAG requires an unconditional EtherChannel with no negotiation protocol.
Cisco 9800-40 WLC high availability with a single controller relies on a Link Aggregation Group (LAG) that bundles distribution ports into an 802.3ad EtherChannel. The correct design is LAG (A), which provides cable-failure redundancy and transparent AP load balancing without LACP or PAgP negotiation.
The most common mistake is choosing LACP (C) or PAgP (D) as the EtherChannel negotiation protocol; however the Cisco 9800 WLC LAG does not support Link Aggregation Control Protocol or Port Aggregation Protocol and must be configured as a static always-on EtherChannel.
Community Discussion (3 comments)
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Expert Analysis
Why the Answer Is Correct
A single Cisco 9800-40 WLC can achieve physical link redundancy by configuring a Link Aggregation Group (LAG), which bundles all of the controller's distribution system ports into one 802.3ad EtherChannel toward the core switch. The Cisco 9800 LAG feature dynamically manages port redundancy and load balances access points transparently to the user, which matches the stated requirements exactly. Because only one WLC is in scope, the design goal is link-level redundancy at the WLC uplink, not controller-stateful failover or multi-switch traffic separation. The LAG must be configured as an unconditional/always-on EtherChannel on the switch side, and the WLC LAG setting then provides the required cable-failure tolerance. Therefore A is the design approach the engineer must take.
Why the Other Options Are Wrong
B, Multi-LAG, is a Cisco 9800 feature that creates multiple LAG interfaces, often for connecting to different switches or separating traffic classes; it is not the documented answer for a single-WLC cable-failure redundancy and transparent AP load-balancing requirement. C, LACP, is an IEEE link aggregation negotiation protocol, but Cisco wireless controllers do not negotiate LAG with LACP; the switch ports must be unconditional. D, PAgP, is Cisco's proprietary negotiation protocol and is likewise unsupported for WLC LAG on the 9800. Both C and D sound plausible because they are standard EtherChannel options, but the question's wording about "dynamically manage port redundancy and perform load balancing between APs transparently" is Cisco's LAG description, not a negotiation-protocol description.
Community Comment Notes
Community comments are unanimous that LAG is correct. zyxzyx123 points to Cisco documentation and explains that a LAG bundles the controller's distribution system ports into a single 802.3ad port channel that "dynamically manages port redundancy and load balances access points transparently." Farhad123 reinforces the single-WLC cable-failure scenario, noting that if one cable fails the other links continue carrying traffic without perceived impact. Lakshan__97 adds the key exam trap: Cisco WLCs "do not support any link aggregation negotiation protocol, like LACP or PAgP," so the switch ports must be an unconditional EtherChannel. These comments align with the vendor behavior and confirm this question's focus on LAG rather than Multi-LAG or negotiation protocols.
Official Reference
Exam Strategy
For 300-425 WLC high-availability questions, identify whether the requirement is controller failover or uplink/port redundancy. Single-WLC cable-failure and transparent AP load balancing point to LAG, and remember the 9800 LAG is an unconditional EtherChannel—not LACP/PAgP.
Frequently Asked Questions
Why is LACP incorrect for the Cisco 9800-40 WLC?
The 9800 WLC LAG does not support LACP or PAgP negotiation; the switch ports must be configured as an unconditional or always-on EtherChannel.
Does Multi-LAG provide better redundancy for a single 9800-40?
Multi-LAG is not the documented feature for this single-WLC cable redundancy scenario; LAG is the mechanism that bundles distribution ports and load-balances APs.