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300-430 · Question #280

An engineer configures Cisco CMX. which uses Layer 2 high availability on primary and secondary CMX instances, according to these specifications: - Primary CMX IP address: 192.168.1.4/24 - Secondary C

The correct answer is D. Place the primary CMX IP address and the secondary CMX IP address in the same subnet.. Cisco CMX Layer 2 HA requires all three IP addresses - primary, secondary, and virtual - to reside on the same subnet. The primary (192.168.1.4/24) and secondary (192.168.4.4/24) are on different subnets, which breaks Layer 2 adjacency required for HA heartbeat communication.

Advanced Location Services

Question

An engineer configures Cisco CMX. which uses Layer 2 high availability on primary and secondary CMX instances, according to these specifications:

  • Primary CMX IP address: 192.168.1.4/24
  • Secondary CMX IP address: 192.168.4.4/24
  • Virtual IP address: 192.168.4.1/24

During testing, the engineer discovers that the failover fails. Which action resolves the issue?

Options

  • APlace the primary CMX IP address and the virtual IP address in the same subnet.
  • BPlace the secondary CMX IP address and the virtual IP address in different subnets.
  • CUse a virtual IP address with CMX Layer 3 high availability.
  • DPlace the primary CMX IP address and the secondary CMX IP address in the same subnet.

How the community answered

(49 responses)
  • A
    4% (2)
  • B
    10% (5)
  • C
    16% (8)
  • D
    69% (34)

Why each option

Cisco CMX Layer 2 HA requires all three IP addresses - primary, secondary, and virtual - to reside on the same subnet. The primary (192.168.1.4/24) and secondary (192.168.4.4/24) are on different subnets, which breaks Layer 2 adjacency required for HA heartbeat communication.

APlace the primary CMX IP address and the virtual IP address in the same subnet.

Placing only the primary and virtual IP in the same subnet still leaves the secondary in a different subnet, which does not satisfy the Layer 2 HA requirement that all three addresses share the same subnet.

BPlace the secondary CMX IP address and the virtual IP address in different subnets.

The secondary and virtual IP must be in the same subnet for Layer 2 HA to function - placing them in different subnets would further break the configuration, not fix it.

CUse a virtual IP address with CMX Layer 3 high availability.

The question specifically asks about Layer 2 HA; switching to Layer 3 HA changes the architecture entirely and does not address the misconfiguration causing the current failover failure.

DPlace the primary CMX IP address and the secondary CMX IP address in the same subnet.Correct

CMX Layer 2 HA relies on a Layer 2 link between the primary and secondary nodes for heartbeat and state synchronization. All three addresses (primary, secondary, and virtual IP) must be in the same subnet. Placing the primary in 192.168.1.0/24 while the secondary and VIP are in 192.168.4.0/24 breaks Layer 2 reachability, causing failover to fail. Placing both primary and secondary in the same subnet as the VIP restores the required Layer 2 adjacency.

Concept tested: Cisco CMX Layer 2 high availability subnet requirements

Source: https://www.cisco.com/c/en/us/td/docs/wireless/mse/10-6/cmx_config/b_CMX_Configuration_Guide_10_6/b_CMX_Configuration_Guide_10_6_chapter_01110.html

Topics

#CMX high availability#Layer 2 HA#subnet configuration#CMX failover

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