How to get sub domain from url using C#

Simple method to get sub domain from url.

/// <summary>
/// Gets the sub domain.
/// </summary>
/// <param name="url">
/// The URL to get the sub domain from.
/// </param>
/// <returns>
/// The sub domain.
/// </returns>
public static string GetSubDomain(Uri url)
{
if (url.HostNameType == UriHostNameType.Dns)
{
var host = url.Host;
if (host.Split(\'.\').Length > 2)
{
var lastIndex = host.LastIndexOf(".");
var index = host.LastIndexOf(".", lastIndex - 1);
return host.Substring(0, index);
}
}
return null;
}