asp.net mvc - Historical URL resolving to new ActionResult instead of 404 -

i have controller has parent , child actionresult.

[route("parent/", name = "parent")] public actionresult parent()  [route("parent/{child}/", name = "child")] public actionresult child(string myparam) 

if put in url www.mysite.com/parent good.

if address child parameter @url.routeurl("child", new { param = myparam }), www.mysite.com/parent/child

however have historical page need 301 www.mysite.com/parent/child.htm.

when put in above url triggers parent actionresult. www.mysite.com/parent when need 301 www.mysite.com/parent/child