The SoBufferedShape node provides a way to specify the indexes for multiple strips or fan in the same index buffer, using a specific value to indicate when starts the next primitive.
For example if the index buffers contains the indices 0 1 2 3 X 4 5 6 7 (where X is the primitive restart index, -1 by default) then the first rendered primitive is 0 1 2 3 and the second one is 4 5 6 7. So the two shapes are rendered using one shape.
When the Primitive Restart is not supported it is possible to specify multiple indices count in the numVertices field.