The Rigid Motion Suppression node adds a minimum number of constraints required to suppress any rigid body modes. The constraints are selected so that there will be no reaction forces if the external loads are self-equilibrating. If you need to constrain several objects which are not physically connected, you must add as many Rigid Motion Suppression nodes as there are disconnected objects.

In the Rigid Motion Suppression node, you cannot access individual layers. Thus the selection in this section only acts as a filter for the boundary selection.

Physics tab with Layered Shell selected:
Boundaries>Face and Domain Constraints>Rigid Motion Suppression