I'm thinking you want an entire animation duplicated? If you mean like a walk cycle or any thing you would want to keep and use in a "library of motions, I would try the motion mixer, you might want to look it up and study the manual because it can get pretty involved. It is very nice because you can create a whole library of motion and use it for getting involved to create rather quickly a whole animation just by using motion mixer to set it up.
If not; I would use the dope track and select the keys and roll them or move them over to repeat any action. You can do the same thing in the graph editor also.
I remember seeing a video that does a good explanation of motion mixer but I can't recall where. Sorry.
Hope that helps a little
