Routing_with_fanout

Hi all,

I'm experiencing a problem about preserving
prerouted nets in  Allegro PCB editor.

In particular, in a first step I've successfully used  the fanout command
for a component.
Next I've started an automatical routing step which should complete
 the existing fanout connections.

I've tried to use the following properties
on fanout connections without  results:

-FIXED,NO_ROUTE: they prevents completing the connections

-NO_RIPUP:it reroutes the connections modifying the existing fanouts.

Could you suggest how to preserve prerouted fanouts
connections from successive autorouting steps?

Thanks,
Giohdl