Cisco 5520 WLC LAG for Redundancy and Load

300-425 By islever Editorial Last updated

Determine physical infrastructure requirements such as AP power, cabling, switch port capacity, mounting, and grounding Design high availability for controllers

Short answer

B Connect a second 10-GB interface on the WLC and implement LAG to increase bandwidth and provide port redundancy.

Question

A customer uses a Cisco 5520 WLC that is connected via a single 10-GB interface to manage the wireless network. The wireless network includes 500 APs for the campus network. The customer wants to add 300 APs and is concerned about traffic load and lack of redundancy. The purchase of a second controller is not an option. Which design approach mitigates the customer concerns?
  1. Connect a second 10-GB interface on the WLC and set the port as a secondary port.
  2. Connect a second 10-GB interface on the WLC and implement LAG. Correct Answer
  3. Implement a vWLC and configure SSO with the WLC.
  4. Implement a vWLC and configure N+1 redundancy with the WLC.

Key Takeaways

LAG on a WLC provides both load balancing and link redundancy, unlike a secondary port which only offers failover redundancy.

Implementing Link Aggregation (LAG) on a Cisco 5520 WLC provides both increased bandwidth and interface redundancy without purchasing a second controller. This approach mitigates traffic load and single-point-of-failure concerns for expanding wireless networks.

Common mistake: Choosing a secondary port configuration (Option A) because it provides redundancy but fails to address the traffic load concern, or choosing a vWLC (Options C/D) which violates the constraint of not purchasing a second controller.

Expert Analysis

Why the Answer Is Correct

Implementing LAG (Link Aggregation Group) on the second 10-GB interface allows both ports to be active simultaneously, effectively doubling the uplink bandwidth to 20 Gbps and providing port redundancy. This directly addresses the customer's concerns about traffic load and lack of redundancy without requiring the purchase of a second controller.

Why the Other Options Are Wrong

Option A (secondary port) provides link redundancy but does not increase bandwidth, as the secondary port only activates if the primary fails. Options C and D involve implementing a vWLC, which constitutes purchasing a second controller and violates the stated constraint. Additionally, as rsbot69420 noted, N+1 redundancy does not solve the traffic load issue on the primary WLC's uplink.

Community Comment Notes

Community members highlighted that a secondary port only offers failover without load balancing, whereas LAG handles both. Lakshan__97 pointed out that a "second WLC is not an option" likely includes virtual controllers, making B the only viable choice. rsbot69420 added that "N+1 doesn't solve the traffic load issue as the main WLC still has all the APs."

Exam Strategy

When a question asks to mitigate both traffic load and redundancy on a single WLC uplink, look for LAG as the solution. Remember that a secondary port provides only failover redundancy, not increased bandwidth.

Community Votes

B
100%

100% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 4 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 4

  1. Lakshan__97 👍 2 Answered B
    B and D can be the answers , since it says purchase an additional controller is not an option (assume that even physical or virtual ). 5520 has 2 x 10Gports . so second port can be connected and make a LAG to increase the bandwisth and port redundancy
  2. rsbot69420 👍 1
    also for D, N+1 doesn't solve the traffic load issue as the main WLC still has all the APs. Therefore, LAG is the most likely solution as it offers higher capacity and additional (uplink) redundancy.
  3. Farhad123 👍 1
    when having second WLC is not an option the only way to increase network resiliency and load balance is to add another interface link and use LAG
  4. Farhad123 👍 1 Answered B
    B is the right solution

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