title: Get netmaske from CIDR
body: <p>How do I get the netmask of any <a href="https://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing" rel="nofollow noreferrer">CIDR</a>, e.g. <br>
  <code>CIDR=10</code> &gt; <code>255.255.0.0</code><br>
  <code>CIDR=24</code> &gt; <code>255.255.255.0</code><br>
  <code>CIDR=25</code> &gt; <code>255.255.255.128</code><br>
  <code>CIDR=31</code> &gt; <code>255.255.255.254</code><br></p>