Periodic mesh in surfaces of porous material

I am working with a porous STL file. The voids in the matrix are positioned randomly but the surfaces of the unit cell are periodic. I would really appreciate your help on how to create a periodic mesh in netgen. Is it possible to do this in an STL file? I am asking because in the examples only CSG models are used. Apologies for the really basic question but I am a fairly new user in netgen.

sorry, periodic boundaries with STL are not possible.
It’s also not something one could add in an afternoon.