Exercise 2: Real Usable Addresses in a /24 Subnet — Possible Solution
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A /24 CIDR block covers 256 total IP addresses (2^8, since 8 bits
are left for host addressing). On paper, that suggests 256 usable
addresses -- but AWS reserves 5 of them in every real subnet for its
own internal use:

  1. The network address itself (the first address in the range)
  2. The VPC router
  3. The DNS server address
  4. Reserved for future AWS use
  5. The broadcast address (the last address in the range) -- even
     though AWS doesn't actually support broadcast, this address is
     still reserved

ANSWER: 256 total addresses minus the 5 AWS reserves leaves 251
real, usable IP addresses for a 10.0.0.0/24 subnet -- not the full
256 the CIDR notation alone might suggest.

WHY THIS WORKS AS AN ANSWER
------------------------------
This correctly applies the specific, real reservation the chapter
names (4 addresses at the start, 1 at the end) rather than just
citing "256 minus a few," and shows the actual arithmetic -- a real,
practical detail that matters when sizing a subnet for a specific
number of instances, since underestimating this reservation can lead
to a subnet running out of usable addresses sooner than expected.