r1 must send a default route to r2 and r3.
r2 must not advertise 2.0.0.0/8 to r3.
r3 must not advertise 3.0.0.0/8 to r3.
On r1:
!
router rip
version 2
redistribute connected metric 2 route-map CONNECTED->RIP
network 12.0.0.0
network 13.0.0.0
default-information originate
distribute-list prefix F0/0 out
!
ip prefix-list F0/0 seq 10 deny 3.0.0.0/8
ip prefix-list F0/0 seq 20 deny 2.0.0.0/8
ip prefix-list F0/0 seq 30 permit 0.0.0.0/0 le 32
!
On r2 and r3, there is now a default route to r1:
r3#sh ip route rip
R 1.0.0.0/8 [120/2] via 13.0.0.1, 00:00:16, Serial0/0
R 12.0.0.0/8 [120/1] via 13.0.0.1, 00:00:16, Serial0/0
R* 0.0.0.0/0 [120/1] via 13.0.0.1, 00:00:16, Serial0/0
R2#sh ip route rip
R 1.0.0.0/8 [120/2] via 12.0.0.1, 00:00:03, Serial0/0
R 13.0.0.0/8 [120/1] via 12.0.0.1, 00:00:03, Serial0/0
R* 0.0.0.0/0 [120/1] via 12.0.0.1, 00:00:03, Serial0/0
R2#
