Simple call your page like this
<iframe src="/ContractReport.aspx?12233"></iframe>
------------- Updated Answer below
Set your URL in controller like this
public ActionResult Index()
{
ViewBag.myURL = "/abc.aspx?" + querystring;
return View();
}
Then in your View,
<iframe id="iframe" src="@Url.Content(ViewBag.myURL)" style="width: 700; height: 700px;"></iframe>