F5-CTS-LTM BIG-IP Local Traffic Manager Practice Question
When configuring a custom monitor, what happens if the 'Time Until Up' is set to 0?
⚠ Common exam trap
Candidates often assume that setting this to 0 disables the monitor entirely, rather than understanding it simply removes the 'slow start' delay for marking a node as 'Up'.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The monitor marks the node as up after the first success.
Setting 'Time Until Up' to zero disables the 'slow start' or 'delayed up' feature of the health monitor. The member is marked 'Up' immediately upon the first successful probe. This is crucial for environments where rapid recovery is required, but it can lead to 'flapping' if the server is unstable. Understanding monitor timing is vital for ensuring high availability without introducing unnecessary instability in the backend pool infrastructure.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The monitor will never mark the node as up.
Why it's wrong here
Setting the value to zero does not disable monitoring; it only adjusts the timing of the transition to the 'Up' state. The system still performs probes, and as long as they return the expected response, the member will be marked as available to process incoming client traffic.
- ✓
The monitor marks the node as up after the first success.
Why this is correct
A value of zero for 'Time Until Up' instructs the BIG-IP to mark a pool member as available immediately after the first successful health check. This provides the fastest possible recovery time for a server returning to the pool, though it risks sending traffic to an un-warmed service.
- ✗
The monitor will fail to send any probes.
Why it's wrong here
Monitor probes are controlled by the 'Interval' and 'Timeout' settings, not the 'Time Until Up' parameter. The monitor will continue to send probes at the configured interval regardless of how the 'Time Until Up' is set, ensuring the BIG-IP maintains continuous oversight of the backend server health.
- ✗
The monitor will use the default system timeout.
Why it's wrong here
The 'Time Until Up' field is independent of the global default timeout settings. Setting it to zero is a specific configuration choice that overrides standard behavior, changing the transition logic specifically for that monitor, rather than reverting to a system-wide default value for the health check success process.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official F5 exam blueprint
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