title: IPAddress.Parse() using port on IPv4
body: <p>I'm trying to parse a string containing an IP address and a port using IPAddress.Parse. This works well with IPv6 addresses but not with IPv4 addresses. Can somone explain why this happens?</p>
  
  <p>The code I'm using is:</p>
  
  <pre><code>IPAddress.Parse("[::1]:5"); //Valid
  IPAddress.Parse("127.0.0.1:5"); //null
  </code></pre>