If RC is a stub router in an OSPF network, it requires a default route to be injected so that it can send traffic outside the OSPF domain. In OSPF, stub routers do not have any routes external to the OSPF domain in their routing tables. To allow these routers to reach networks outside of their OSPF domain, a default route should be injected into the stub area by the Area Border Router (ABR). This allows all routers in the stub area, including RC, to forward traffic for unknown destinations to the ABR, which then forwards it appropriately. References: Implementing and Operating Cisco Service Provider Network Core Technologies source documents or study guide