实验环境：

操作系统：Mac OS X 10.11.4（当时最新正式版），模拟器：GNS3 IOU for Mac 1.4.4（当时最新版本）
注：当然，只要有思科模拟器都可以做这个实验

实验过程：

完成上述配置后，我们在IOU3上看一下来自IOU5的5.5.5.5的路由：

IOU3#sh ip ro
Codes: L - local, 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, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override

Gateway of last resort is not set

      1.0.0.0/32 is subnetted, 1 subnets
O IA     1.1.1.1 [110/21] via 23.1.1.2, 00:01:59, Ethernet0/1
      2.0.0.0/32 is subnetted, 1 subnets
O IA     2.2.2.2 [110/11] via 23.1.1.2, 00:01:59, Ethernet0/1
      3.0.0.0/32 is subnetted, 1 subnets
C        3.3.3.3 is directly connected, Loopback0
      4.0.0.0/32 is subnetted, 1 subnets
O IA     4.4.4.4 [110/21] via 35.1.1.5, 00:01:13, Ethernet0/0
      5.0.0.0/32 is subnetted, 1 subnets
O        5.5.5.5 [110/11] via 35.1.1.5, 00:01:13, Ethernet0/0
                                          —— 这里是O的路由，因为他们同属于area 1
......

然后我们到IOU3上shutdown掉e 0/0：

IOU3#sh ip ro
Codes: L - local, 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, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override

Gateway of last resort is not set

      1.0.0.0/32 is subnetted, 1 subnets
O IA     1.1.1.1 [110/21] via 23.1.1.2, 00:03:45, Ethernet0/1
      2.0.0.0/32 is subnetted, 1 subnets
O IA     2.2.2.2 [110/11] via 23.1.1.2, 00:03:45, Ethernet0/1
      3.0.0.0/32 is subnetted, 1 subnets
C        3.3.3.3 is directly connected, Loopback0
      4.0.0.0/32 is subnetted, 1 subnets
O IA     4.4.4.4 [110/31] via 23.1.1.2, 00:00:20, Ethernet0/1
      5.0.0.0/32 is subnetted, 1 subnets
O IA     5.5.5.5 [110/41] via 23.1.1.2, 00:00:20, Ethernet0/1
               —— 虽然同属于area 1，但是这条路由来自骨干区域area 0，所以是O IA的路由了