Exercise 2: Why "No Rule Found on the Host Firewall" Isn't Conclusive — Possible Solution
====================================================================

WHY THE COLLEAGUE'S CONCLUSION ISN'T SAFE
------------------------------
Per this chapter's warn-box, "real environments frequently stack
several independent firewall layers - a host-based firewall on the
server itself, a network appliance, and a cloud security group, any of
which could be the one actually blocking traffic." Checking the host's
own firewall only rules out that one specific layer - it says nothing
about any of the other layers that might also be in the path.

THE CHAPTER'S OWN PRINCIPLE
------------------------------
Per this chapter, "having checked one layer and found nothing doesn't
rule out a block at a layer you don't have visibility into at all.
Absence of evidence, in a layer you can't actually see, is not
evidence of absence." The colleague's conclusion treats "I checked the
one layer I have access to" as equivalent to "I checked everywhere,"
which the chapter explicitly says isn't the same thing.

WHAT WOULD ACTUALLY SUPPORT RULING OUT A FIREWALL
------------------------------
Confirming every layer in the actual path - not just the host firewall
- would be needed, and even then, a layer the engineer has no access to
at all (e.g. a cloud security group managed by another team) can't be
positively ruled out without someone who has visibility into it
checking directly.

WHY THIS WORKS AS AN ANSWER
------------------------------
It identifies specifically which layer the colleague checked versus
which layers remain unchecked, and applies the chapter's own explicit
"absence of evidence" reasoning rather than a generic "you can't be
sure" statement.