To ensure that all Internet traffic is directed through R1, the local preference BGP attribute should be used. Local preference is an attribute that influences the outbound traffic from an Autonomous System (AS). By setting a higher local preference on the route received via R1 compared to the route received via R2, the routers within the AS will prefer the path through R1 for outgoing traffic. This allows you to control the exit point for specific traffic within your network, making R1 the primary route for all Internet traffic.