I can answer the question, sir, if you want.
If you look at the occupied territories—and I wish I had my map here—a significant portion of the Ukrainian territory, or the border that used to be the Ukrainian border with Russia, right now is not controlled by Ukrainian forces at all. It is under the control of the Russian forces and the Russian proxy forces.
To answer your question, no, it is not porous; it is completely open. Equipment, troops, FSB agents, or whoever, are being moved freely back and forth between the occupied territories and Russia. Ukraine has no control over those border lengths in the occupied regions whatsoever.