title: X509 subject alternative name (subjectAltName) IP address field
body: <p>X509v3 can contain <code>IP</code> address field in <code>subject Alternative Name</code> extension. </p>
  
  <ol>
  <li>As an application verifying the server's identity, how should the IP address field be validated? </li>
  <li>If both DNS name and IP address are present? Is there a preference of one over the another?</li>
  <li>What is the use of <code>dirName</code> field?</li>
  </ol>