400-007 · Question #250
A business invests in SDN and develops its own SDN controller that, due to budget constraints, runs on a single controller. The controller actively places an exclusive lock on the configuration of…
The correct answer is B. All device configurations are in read-only mode until the controller is restored. When an SDN controller holds an exclusive lock on device configurations and then fails, no entity can modify those configurations, leaving all devices in a read-only state until the controller recovers.
Question
A business invests in SDN and develops its own SDN controller that, due to budget constraints, runs on a single controller. The controller actively places an exclusive lock on the configuration of the devices to ensure it is the only source of changes to the environment. What is the result if the controller fails?
Options
- AManual changes are only possible until the controller is restored
- BAll device configurations are in read-only mode until the controller is restored
- CThe control plane is unavailable until the controller is restored
- DIf a device fails, the configuration backup is unavailable
How the community answered
(32 responses)- A3% (1)
- B75% (24)
- C6% (2)
- D16% (5)
Why each option
When an SDN controller holds an exclusive lock on device configurations and then fails, no entity can modify those configurations, leaving all devices in a read-only state until the controller recovers.
Manual changes are not 'only possible' in a reduced capacity - they are completely blocked by the exclusive lock, so this choice underrepresents the actual restriction imposed.
The controller acquired an exclusive lock on all device configurations before failing. Because the lock is still held by the crashed controller and cannot be released, no other process or administrator can write new configurations, effectively placing every device in read-only mode until the controller is restored and the lock is freed.
The data and control planes on individual devices continue to function using their existing forwarding tables; only the ability to push configuration changes is blocked, not the control plane operation itself.
The exclusive configuration lock has no direct relationship to configuration backup availability; backup mechanisms are separate and are not affected by the lock state.
Concept tested: SDN single controller failure impact with exclusive configuration lock
Source: https://www.cisco.com/c/en/us/solutions/software-defined-networking/overview.html
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