How get external IP address

public static void GetLoginIP()
    {
        try
        {
            if(Session["IP"] == null)
{
            String strIP = "";
            WebRequest request = WebRequest.Create("http://checkip.dyndns.org/");
            using (WebResponse response = request.GetResponse())
            using (StreamReader stream = new StreamReader(response.GetResponseStream()))
            {
                strIP = stream.ReadToEnd();
            }
            int first = strIP.IndexOf("Address: ") + 9;
            int last = strIP.LastIndexOf("</body>");
            strIP = strIP.Substring(first, last - first);

            Session["IP"] = strIP;
}
        }
        catch(Exception Ex)
        {

        }

    }