Exercise 1: Why DNS Comes Before Network Reachability — Possible Solution
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THE TEXTBOOK ORDERING VS. THE PRACTICAL ORDERING
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Per this chapter, DNS is formally an application-layer protocol, sitting
above the network layer, so a strict OSI-purist ordering would test raw
network reachability before ever touching DNS. This chapter's practical
ladder deliberately puts DNS second instead, right after local
connectivity.

WHY: EVERY LATER TEST DEPENDS ON HAVING THE RIGHT ADDRESS
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Per this chapter, "almost every later test in this ladder needs a
correct IP address to test against." If DNS resolves a name to the
wrong IP, every network-reachability, port, and application test that
follows will faithfully test the wrong destination - producing
confusing, misleading results that look like failures in those layers,
when the real problem was the address itself.

IT'S ABOUT NOT WASTING THE REST OF THE LADDER, NOT OSI PURITY
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Per this chapter, checking DNS early "isn't about OSI purity; it's
about not wasting the rest of the ladder on a bad starting address."
The chapter is explicit that this is a deliberate, practical deviation
from the formal layer order, not a claim that DNS actually belongs
lower in the OSI stack.

WHY THIS WORKS AS AN ANSWER
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It correctly identifies that the deviation is intentional and explains
the specific practical reason (a wrong IP would corrupt every test that
follows), rather than either ignoring the OSI-layer discrepancy or
incorrectly claiming DNS is formally a lower-layer protocol.