web获得IP 地址

public static class Comm
　{
    /// <summary>
    /// 获得IP地址
    /// </summary>
    /// <param name="request"></param>
    /// <returns></returns>
    public static string GetIPstring(HttpRequest request)
    {
        // 穿过代理服务器取远程用户真实IP地址
        string Ip = string.Empty;
        if (request.ServerVariables["HTTP_VIA"] != null)
        {
            if (request.ServerVariables["HTTP_X_FORWARDED_FOR"] == null)
            {
                if (request.ServerVariables["HTTP_CLIENT_IP"] != null)
                    Ip = request.ServerVariables["HTTP_CLIENT_IP"];
                else
                    if (request.ServerVariables["REMOTE_ADDR"] != null)
                        Ip = request.ServerVariables["REMOTE_ADDR"];
                    else
                        Ip = "0.0.0.1";
            }
            else
                Ip = request.ServerVariables["HTTP_X_FORWARDED_FOR"];
        }
        else if (request.ServerVariables["REMOTE_ADDR"] != null)
        {
            Ip = request.ServerVariables["REMOTE_ADDR"];
        }
        else
        {
            Ip = "0.0.0.1";
        }
        return Ip;
    }
}

string str_ip=Comm.GetIPstring(Request);