Rewrite URL using irule from internal to External

Presumably it does that because the new request comes in with a Host header of so it doesn't match your iRule. I think you need to go back to the drawing board to work out what you want it to do and the flow because you're going to struggle otherwise. You could rewrite the HTML coming through, or make sure you send them to a page on which they can't access specific links ie everything is relative.