I am searching for a book that I read a long time ago.
It is set in a world with two societies, one living in sealed, high-tech cities, and one living a primitive lifestyle in the jungle or forest - they are all human though.
Occasionally the two sides meet to trade but it is the city-dwellers who have the power, which they maintain through robot dogs patrolling outside.
The inner workings of these dogs are exposed (they are not disguised as real dogs).
One character (the protagonist, I think) finds a screwdriver and takes it to an elder in his village and asks him whether it could be used as a weapon against the dogs. The old man laughs and says that the dog would kill him before he even got the first screw out. The young man then asks what a screw is. So the old man was either privy to some handed-down knowledge, or remembers the world before the split into the two factions.
Are there any ideas what this book could be?