Routing on top and bottom side is possible with any option on etch???

Hi..

I had worked on the pcb with two layer board. In old days worked with the layout i use to route the enabled ratsnest on top side, at connection tool----> make and connection between source to destination with connection tool.. Then put the route by bottom on the connection enabled by tool.                       Still my doubt is i had put the etch(top) on my board and then if need to try route the etch on bottom side means how it is possible.

Can any provide any solution for this.      

Thanks & regards  Dhamodharan