r1----
sys
sysnam r1
int g0/0/1
ip add 12.0.0.1 24
ospf netw p2p
int g0/0/0
ip add 10.0.0.1 24
ospf netw p2p
int l0
ip add 1.1.1.1 32
ospf 1 rou 1.1.1.1 
a 0
netw 12.0.0.1 0.0.0.0
netw 1.1.1.1 0.0.0.0
a 1 
netw 10.0.0.1 0.0.0.0

r2---------
sys
sysnam r2
int g0/0/1
ip add 12.0.0.2 24
ospf netw p2p
int g0/0/0
ip add 20.0.0.1 24
ospf netw p2p
int l0
ip add 2.2.2.2 32
ospf 1 rou 2.2.2.2
a 0
netw 12.0.0.2 0.0.0.0
netw 2.2.2.2 0.0.0.0
a 2
netw 20.0.0.1 0.0.0.0

r3-----
sys
sysnam r3
int g0/0/0
ip add 10.0.0.2 24
ospf netw p2p
int l0
ip add 3.3.3.3 32
ospf 1 rou 3.3.3.3 
a 1
netw 3.3.3.3 0.0.0.0
netw 10.0.0.2 0.0.0.0

r4-----
sys
sysnam r4
int g0/0/0
ip add 20.0.0.2 24
ospf netw p2p
int l0
ip add 4.4.4.4 32
ospf 1 rou 4.4.4.4
a 2
netw 4.4.4.4 0.0.0.0
netw 20.0.0.2 0.0.0.0