For full reachability between AS 1000 and AS 2000, R1 needs to advertise network 192.168.0.0 (option A) and R2 needs to advertise network 209.165.201.0 (option D). These commands ensure that both Autonomous Systems are aware of each other's networks, enabling full reachability between them as per the BGP routing protocol's operation.References := Cisco BGP Configuration Guide