In a small hub and spoke (where spokes are stubs) you could use On Demand Routing (ODR) to achieve full readability between sites. ODR uses CDP as its transport . CDP versions must match. ODR will auto-inject a default route in the spoke routers and the spoke routers will advertise their directly connected networks to the hub router. On the hub router enable ODR and ensure you have CDP neighbours to spokes;

router odr