r1: 
conf t 
int s1 
clockrate 64000 
ip add 12.0.0.1 255.255.255.252 
no shut 
int e0 
ip add 1.1.1.1 255.255.255.0 
no shut 
exit 
router ospf 10 
network 1.1.1.0 0.0.0.255 area 0 
network 12.0.0.0 0.0.0.3 area 0 
r2: 
conf t 
int s1 
ip add 12.0.0.2 255.255.255.252 
no shut 
int e0 
ip add 2.2.2.1 255.255.255.0 
no shut 
int s2 
clockrate 64000 
ip add 23.0.0.1 255.255.255.252 
no shut 
exit 
router ospf 10 
network 2.2.2.0 0.0.0.255 area 0 
network 23.0.0.0 0.0.0.3 area 0 
r3: 
conf t 
int s2 
ip add 23.0.0.2 255.255.255.252 
no shut 
int e0 
ip add 3.3.3.1 255.255.255.0 
no shut 
exit 
router ospf 10 
network 3.3.3.0 0.0.0.255 area 0 
network 23.0.0.0 0.0.0.3 area 0