Tell me about an outage you caused. What happened and what did you learn?
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Say this first
Use your own real story. A model answer, STAR shaped: during a planned change I added a VLAN to a
distribution trunk with switchport trunk allowed vlan 40 instead of switchport trunk allowed vlan add 40, which
removed every other VLAN and cut off two floors. I saw the alarm, recognized my change, restored the
list from my pre-change capture and told the incident lead at once. Users were down about six minutes.
I wrote the review and we added peer-reviewed scripts and an automatic post-check for trunk changes.
Go deeper
What the interviewer is testing
Ownership, honesty, how fast you recover, how you communicate, and whether you fix the system instead of promising to "be more careful". Everyone senior has caused an outage. Claiming you never have is a red flag.
The model, step by step
- Situation: a planned evening change to add a VLAN for new conference room equipment on a distribution trunk serving two floors.
- Task: the change was mine. When it went wrong, so was the recovery and the explanation.
- Action: monitoring alarmed within a minute. Mine was the only change in progress, so I checked
show interfaces trunk, saw the allowed list reduced to VLAN 40, and restored it from my pre-change output. I told the incident lead and service desk what had happened before anyone asked. The next day I wrote a blameless post-incident review with the timeline and root cause. - Result: about six minutes of impact. We added two controls: trunk changes use reviewed command scripts, and a post-check compares the allowed VLAN list before and after. That class of error did not happen again.
- Lesson: the process allowed one mistyped word to take down two floors; a review and an automatic check removed that path.
Adapting it
Pick a real outage you were part of, keep it under two minutes, give numbers (duration, users, services), and spend most of the time on actions and what changed afterwards.
They will ask next
What would you do differently today?
Answer with a concrete control, not a feeling: "I would have had the post-check script run automatically", not "I would be more careful".
How did you communicate during the outage?
Say who you told, when, and what you said. Telling the incident lead early that your change was the likely cause is what interviewers want to hear.
Traps
- Blaming a colleague, the vendor or the process without owning your part.
- A story with no real mistake in it, or no measurable result.
- Inventing a story. Follow-up questions expose it quickly.