Exercise 3: The Ticket's Real Root Cause, and Why Finishing the Ladder Still Mattered — Possible Solution
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THE REAL ROOT CAUSE
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Per this chapter, "this ticket's real root cause was the stale DNS
answer identified back in Chapter 4." Once that single rung was
corrected, local connectivity, network reachability, and port
reachability were all already fine - there was never a separate
firewall or application-layer problem underneath it.

WHY CONFIRMING THE LATER RUNGS WAS STILL WORTH DOING
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Per this chapter, "it would have been easy to spend far longer
investigating firewalls or application logs for a problem that was
actually settled two chapters ago." Without actually testing the
network path (Chapter 5) and the port (Chapter 6), there would be no
confirmed evidence that the DNS fix was actually sufficient - only an
assumption. Working the remaining rungs turned "we think the DNS fix
solved it" into a confirmed, evidence-backed statement that nothing
else in the path is broken.

WHY THIS IS THE LADDER'S OWN PAYOFF
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Per this chapter, this is "exactly the payoff the ladder is built
for" - stopping at the first failing rung finds the cause quickly, and
continuing to confirm the remaining rungs (rather than assuming they're
fine) is what actually proves the fix worked, rather than just hoping
it did.

WHY THIS WORKS AS AN ANSWER
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It correctly identifies the DNS issue from Chapter 4 as the actual root
cause, and explains - using the chapter's own reasoning - why testing
the remaining rungs after finding the cause still had real diagnostic
value (confirming the fix, not just assuming it), rather than treating
the later checks as redundant busywork.