6.0.0.0/32 is subnetted, 1 subnets
C 6.6.6.6 is directly connected, Loopback0
C 192.168.36.0/24 is directly connected, FastEthernet0/0
O*IA 0.0.0.0/0 [110/11] via 192.168.36.3, 00:00:07, FastEthernet0/0
由此可知stub区域不接收任何外部路由，用一条默认路由替代所有外部路由。
先在R4上查看路由表：
O IA 192.168.123.0/24 [110/20] via 192.168.14.1, 00:00:51, FastEthernet0/0
1.0.0.0/32 is subnetted, 1 subnets
O IA 1.1.1.1 [110/11] via 192.168.14.1, 00:00:51, FastEthernet0/0
2.0.0.0/32 is subnetted, 1 subnets
O IA 2.2.2.2 [110/21] via 192.168.14.1, 00:00:51, FastEthernet0/0
C 192.168.14.0/24 is directly connected, FastEthernet0/0
3.0.0.0/32 is subnetted, 1 subnets
O IA 3.3.3.3 [110/21] via 192.168.14.1, 00:00:51, FastEthernet0/0
O IA 192.168.25.0/24 [110/30] via 192.168.14.1, 00:00:52, FastEthernet0/0
4.0.0.0/32 is subnetted, 1 subnets
