Why Does Cisco CMX Layer 2 HA Failover Fail?
Short answer
D For Cisco CMX Layer 2 high availability, place the primary and secondary CMX IP addresses in the same subnet so the virtual IP can fail over.
Question
Key Takeaways
Tested: CMX Layer 2 HA addressing rules; the trap is focusing only on the VIP and primary while ignoring the primary-to-secondary subnet mismatch.
Cisco CMX Layer 2 high availability requires the primary and secondary instances and the virtual IP to share the same subnet. This page confirms that moving the primary and secondary CMX addresses into one subnet (D) resolves the failover failure.
Common mistake: Many learners choose A, moving the primary and VIP into the same subnet, but Layer 2 HA needs the primary and secondary CMX addresses in the same subnet as each other and the VIP; fixing only the VIP mismatch leaves the real separation unresolved.
Expert Analysis
Why the Answer Is Correct
Cisco CMX Layer 2 HA requires all three addresses — primary, secondary, and virtual IP — to be in the same Layer 2 subnet because failover moves the VIP between the two physical CMX nodes via ARP. In the scenario, primary 192.168.1.4/24 and secondary 192.168.4.4/24 sit in different subnets, so the VIP 192.168.4.1/24 can never be claimed by the primary after failover. Option D fixes this by placing the primary and secondary CMX IP addresses in the same subnet, which inherently allows the VIP to remain reachable on both nodes. Community consensus agrees: as learn4team put it, "Both primary and secondary must be on the same subnet," and casterJR stated the answer is D. Therefore D is the correct remediation.
Why the Other Options Are Wrong
Option A only aligns the primary CMX IP with the virtual IP; even if the VIP were moved to 192.168.1.0/24, the secondary would still be stranded in 192.168.4.0/24 and Layer 2 failover would still break. Option B makes the split worse by explicitly separating the secondary from the VIP, which is the opposite of what CMX Layer 2 HA needs. Option C suggests switching to Layer 3 HA, but the question states the design uses Layer 2 HA and asks for the action that resolves the current failure, not a redesign. Option D is the only choice that repairs the underlying Layer 2 subnet requirement while preserving the stated CMX HA mode.
Community Comment Notes
Most commenters converged on D. learn4team cited Cisco documentation and emphasized that both CMX nodes must share a subnet so the VIP can switch between them. rrahim explained that the VIP must also be in the same subnet as both primary and secondary addresses, which aligns with the Layer 2 HA requirement. hirendra summarized it simply: "all devices should be in same subnet." One commenter, hirendra separately, argued for A, but that suggestion only fixes part of the addressing mismatch and does not satisfy the Layer 2 HA requirement for the secondary node.
Official Reference
This link opens the official vendor documentation in a new tab.
Exam Strategy
When a CMX HA question gives three addresses, check them against the HA mode before reading the options. Layer 2 HA requires primary, secondary, and VIP in the same subnet, so any option that only fixes one address pair is a partial fix. Verify the exact CMX mode stated (Layer 2 vs Layer 3) before choosing a remediation.
Frequently Asked Questions
Why can't the primary CMX IP and the virtual IP alone share a subnet?
Does Cisco CMX Layer 3 high availability allow different subnets?
Community Votes
100% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.
Discussion 6 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 6
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learn4team 👍 3 Answered DThe primary and secondary must be reachable between each system. Both primary and secondary must be on the same subnet. This is required so the virtual IP address used can be switched to either system. https://www.cisco.com/c/en/us/support/docs/availability/high-availability/213664-configure-cmx-high-availability.html#anc5
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rrahim 👍 1 Answered DD. Place the primary CMX IP address and the secondary CMX IP address in the same subnet. For Layer 2 high availability (HA) to work correctly in Cisco CMX, the primary CMX IP address and the secondary CMX IP address must be in the same subnet. The virtual IP address (VIP) must also be in the same subnet as both the primary and secondary IP addresses. In the given scenario, the primary and secondary CMX IP addresses are in different subnets, which is causing the failover to fail.
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largestyle 👍 1If the primary and secondary need to be in the same subnet the answer must be "Place the primary CMX IP address and the secondary CMX IP address in the same subnet." https://www.cisco.com/c/en/us/td/docs/wireless/mse/10-6/cmx_config/b_cg_cmx106/managin g_cisco_cmx_system_settings.html#concept_88FD92666F8140A980280E009C45152F
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hirendra 👍 1its Layer 2 HA, all devices should be in same subnet
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casterJR 👍 1Correct answer is D
Show 1 more comment
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hirendra 👍 1answer should be A
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