You can use TempData. You can transfer all types of data between actions, regardless of whether they are in the same controller or not. Your code should look something like this:
public ActionResult GetMDN(string msisdn)
{
int sngid=10;
TempData["ID"] = sngid;
return RedirectToAction("IIndex");
}
public ActionResult IIndex()
{
int id = Convert.ToInt32(TempData["ID"]);
}