Extracting the Extension of a Url Host

var host = this.Request.Url.Host;
private string ExtractExtension(string host)
{
   string result = null;
   var pattern = @"[\w-]+\.[\w-]+(?<extension>(\.[\w-]+)+)";
   var match = Regex.Match(host , pattern);
   if (match.Groups["extension"].Success)
   {
      result = match.Groups["extension"].Value;
   }
   return result;
}

Note: this method is easily testable.