Your question is First Step When Fiber Link Fails. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
What is your first step when a fiber link goes down at both ends?
Answer in the context of an AWS production network incident. Focus on the immediate triage action, what you verify before changing anything, and how you avoid making the outage worse.