title: Regex for IPaddress/prefix
body: <p>I have a regex for IP address validation, but I need a regex for prefix validation, where the expected form is "IP Address/Prefix".</p>
  
  <p>The conditions are:</p>
  
  <ol>
  <li><p>The prefix value should not be greater than 128</p></li>
  <li><p>The prefix value should be divisible by 4.</p></li>
  </ol>
  
  <p>Could anyone please help me to create a regex for prefix validation?</p>