R1:
interface Loopback0
 ip address 1.1.1.1 255.255.255.255
interface FastEthernet0/0
 ip address 12.1.1.1 255.255.255.0
router ospf 1
 router-id 1.1.1.1
 area 1 nssa
 network 1.1.1.1 0.0.0.0 area 1
 network 12.1.1.0 0.0.0.255 area 1

R2:
interface Loopback0
 ip address 2.2.2.2 255.255.255.255
interface FastEthernet0/0
 ip address 12.1.1.2 255.255.255.0
interface FastEthernet0/1
 ip address 23.1.1.2 255.255.255.0
router ospf 1
 router-id 2.2.2.2
 area 1 nssa default-information-originate //解决外部rip路由无法传递过来。
 network 2.2.2.2 0.0.0.0 area 0
 network 12.1.1.0 0.0.0.255 area 1
 network 23.1.1.0 0.0.0.255 area 0

R3:
interface Loopback0
 ip address 3.3.3.3 255.255.255.255
interface FastEthernet0/0
 ip address 34.1.1.3 255.255.255.0
interface FastEthernet0/1
 ip address 23.1.1.3 255.255.255.0
router ospf 1
 router-id 3.3.3.3
 redistribute rip subnets
 network 3.3.3.3 0.0.0.0 area 0
 network 23.1.1.0 0.0.0.255 area 0
router rip
 version 2
 redistribute ospf 1 metric 2
 network 34.0.0.0
 no auto-summary

R4:
interface Loopback0
 ip address 4.4.4.4 255.255.255.255
interface FastEthernet0/0
 ip address 34.1.1.4 255.255.255.0
router rip
 version 2
 network 4.0.0.0
 network 34.0.0.0
 no auto-summary


R4(config)#do show ip route rip
     1.0.0.0/32 is subnetted, 1 subnets
R       1.1.1.1 [120/2] via 34.1.1.3, 00:00:00, FastEthernet0/0
     2.0.0.0/32 is subnetted, 1 subnets
R       2.2.2.2 [120/2] via 34.1.1.3, 00:00:00, FastEthernet0/0
     3.0.0.0/32 is subnetted, 1 subnets
R       3.3.3.3 [120/2] via 34.1.1.3, 00:00:00, FastEthernet0/0
     23.0.0.0/24 is subnetted, 1 subnets
R       23.1.1.0 [120/2] via 34.1.1.3, 00:00:00, FastEthernet0/0
     12.0.0.0/24 is subnetted, 1 subnets
R       12.1.1.0 [120/2] via 34.1.1.3, 00:00:00, FastEthernet0/0

R4(config)#do ping 1.1.1.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 44/50/60 ms