C#获取用户登录IP地址

public static string GetUserIp()
{
      string ip;
      string[] temp;
      bool isErr = false;
      if (System.Web.HttpContext.Current.Request.ServerVariables["HTTP_X_ForWARDED_For"] == null)
      {
         ip = System.Web.HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"].ToString();
      }
      else
      {
         ip = System.Web.HttpContext.Current.Request.ServerVariables["HTTP_X_ForWARDED_For"].ToString();
      }
      if (ip.Length > 15)
      {
        isErr = true;
      }
      else
      {
        temp = ip.Split('.');
        if (temp.Length == 4)
        {
        for (int i = 0; i < temp.Length; i++)
       {
         if (temp[i].Length > 3) isErr = true;
       }
    }
    else
      isErr = true;
   }
   if(isErr)
   {
     return "1.1.1.1";
   }
   else
  {
    return ip;
  }
}