■

再配送はちょっと難しいですね。
CCNAの試験で設定はでないものと思われます。
実質、CCNPの内容じゃないでしょうか。
この程度が出来ただけでは、再配送が理解できていることにはならないと思うのでなんか腑に落ちない感じです。
ということで、この勝負CCNPに持ち越しですね。

■R1
R1(config)#int fa0/0
R1(config-if)#ip address 172.16.0.1 255.255.0.0
R1(config-if)#no shut
R1(config-if)#int s1/0
R1(config-if)#ip address 172.20.0.1 255.255.0.0
R1(config-if)#no shut
R1(config-if)#end
R1#conf t
R1(config)#router rip
R1(config-router)#network 172.16.0.0
R1(config-router)#network 172.20.0.0

■R2
R2(config)#int s1/0
R2(config-if)#ip address 172.20.0.2 255.255.0.0
R2(config-if)#clock rate 64000
R2(config-if)#no shut
R2(config-if)#int s1/1
R2(config-if)#ip address 172.21.0.2 255.255.0.0
R2(config-if)#clock rate 64000
R2(config-if)#no shut
R2(config-if)#exit

■R3
R3(config)#int s2/0
R3(config-if)#ip address 172.21.0.3 255.255.0.0
R3(config-if)#no shut
R3(config-if)#int fa0/0
R3(config-if)#ip address 172.31.0.3 255.255.255.0
R3(config-if)#no shut
R3(config-if)#end
R3(config)#router ospf 100
R3(config-router)#network 172.31.0.0 0.0.0.255 area 0
R3(config-router)#network 172.21.0.0 0.0.255.255 area 0
R3(config-router)#end

■R2で再配送の設定をする←ここが本題です。
R2(config)#router ospf 100
R2(config-router)#redistribute rip metric 100 subnets
R2(config-router)#network 172.21.0.0 0.0.255.255 area 0
R2(config-router)#
00:20:13: %OSPF-5-ADJCHG: Process 100, Nbr 172.31.0.3 on Serial1/1 from LOADING to FULL, Loading Done←アジャセンシーの関係を形成しました。
R2(config-router)#exit
R2(config)#router rip
R2(config-router)#redistribute ospf 100 metric 2
R2(config-router)#network 172.20.0.0
R2(config-router)#exit

■R2のルーティングテーブルを確認する
R2#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

R 172.16.0.0/16 [120/1] via 172.20.0.1, 00:00:15, Serial1/0
C 172.21.0.0/16 is directly connected, Serial1/1
C 172.20.0.0/16 is directly connected, Serial1/0
172.31.0.0/24 is subnetted, 1 subnets
O 172.31.0.0 [110/65] via 172.21.0.3, 00:02:06, Serial1/1

■R1のルーティングテーブルを確認する
R1#sh ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

C 172.16.0.0/16 is directly connected, FastEthernet0/0
R 172.21.0.0/16 [120/2] via 172.20.0.2, 00:00:25, Serial1/0
C 172.20.0.0/16 is directly connected, Serial1/0
R 172.31.0.0/16 [120/2] via 172.20.0.2, 00:00:25, Serial1/0

■R3のルーティングテーブルを確認する
R3#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

O E2 172.16.0.0/16 [110/100] via 172.21.0.2, 00:03:10, Serial2/0
C 172.21.0.0/16 is directly connected, Serial2/0
O E2 172.20.0.0/16 [110/100] via 172.21.0.2, 00:03:10, Serial2/0
172.31.0.0/24 is subnetted, 1 subnets
C 172.31.0.0 is directly connected, FastEthernet0/0