I inherited a Expedition design. I would like to grow the board, which I have done and add my portion of the design which together with the parts that were on the board before I took it over would comprise the whole board. I would like to lock down the components and traces that I inherited. I have already place all of my components that were not on the original design. Now I would like to start routing my portion of the board. I would only like to route on the top and the bottom layers. I have placed planes in the inner layers under my portion of the board, and I don't want traces to be routed on those inner layers. The inherited portion of the board has traces routed on those inner layers. I would like to route by hand the critical traces on my portion of the board and then use the autorouter to route the rest of the traces on my portion of the board. Mind you that the inner layers are not defined as planes, I drew planar areas on the inner layers for my "ground plane" for instance. I attached a bitmap file showing the board.
My question is:
How do I specify that the autorouter only route on the top and bottom layer given the information described above.