Flushing Active Route Table

I still can’t see why it should be a problem to give the second interface a separate network. After all, you have to assign some address to it, so why not make it one that will effectively isolate the networks in the way that you require? It’s much more difficult to isolate some device from others on the same network (I’d use a firewall if I had that requirement).

Having said that, I’m not sure why a specific persistant route shouldn’t work, although it is more work, if you specify the appropriate interface. But it’s not something that I have ever had the occasion to try; I’ve always found a private network for the isolated devices to be the most logical solution.

Perhaps I still don’t understand your requirements.