title: how many machines can actually be connected on the internet using IPV4?
body: <p>Recently we were talking about IP addresses running out. I was wondering how many machines can we connect on the internet before IP addresses run out. My calculation went something like this.</p>
  
  <pre><code>Class A - 2 ^ 31 (7 bits Network Id + 24 bits Host Id.)
  Class B - 2 ^ 30 (14 bits Network Id + 16 bits Host Id.)
  Class C - 2 ^ 29 (21 bits Network Id + 8 bits Host Id.)
  Class D - 2 ^ 28 (28 bits multicast group Id.)
  Class E  - 0 Reserved for future use.
  </code></pre>
  
  <p>So the total number of machines that is allowed on the internet should be </p>
  
  <pre><code>2^31 + 2^30 + 2^29 + 2^28 = 2^28(1 + 2 + 4 + 8) = 15 * 2^28.
  </code></pre>
  
  <p>Does this calculation seem correct?</p>