title: Basics about IP addressing
body: <p>let's say that we have a router with address: <strong>172.31.219.33/27</strong> from this I can tell several things:</p>
  
  <ol>
  <li>Subnet mask: <strong>255.255.255.224</strong></li>
  <li>Broadcast address (here I am not sure if last digit should 64 or 65 - see later): <strong>172.31.219.64</strong></li>
  <li>Last host address (since we know broadcast address; also not sure if last digit should be 63 or 62): <strong>172.31.219.63</strong></li>
  </ol>
  
  <p>We could also tell first host address (<strong>172.31.219.33</strong>) and network address (<strong>172.31.219.32</strong>).</p>
  
  <p>I don't understand two things:</p>
  
  <ol>
  <li>Why is first host address <strong>X.X.X.33</strong>? It is like the router is already a host?</li>
  <li>Why is network address <strong>X.X.X.32</strong>? In other way, why it is not <strong>X.X.X.33</strong> (from router address)?</li>
  </ol>
  
  <p>EDIT: Could also anyone tell me why it is B-class address and not C-class (since mask for C-class is <strong>255.255.255.0 - 255.255.255.254</strong>)?</p>