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

　　1.0.0.0/24 is subnetted, 1 subnets

　　S 1.1.1.0 [1/0] via 172.1.1.1

　　2.0.0.0/24 is subnetted, 1 subnets

　　C 2.2.2.0 is directly connected, Loopback0

　　3.0.0.0/24 is subnetted, 1 subnets

　　i L1 3.3.3.0 [115/20] via 172.2.1.2, Serial0/1

　　172.1.0.0/24 is subnetted, 1 subnets

　　C 172.1.1.0 is directly connected, Serial0/0

　　172.2.0.0/24 is subnetted, 1 subnets

　　C 172.2.1.0 is directly connected, Serial0/1

　　在路由器3上查看路由表

　　r3#show 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

　　1.0.0.0/24 is subnetted, 1 subnets

　　i L2 1.1.1.0 [115/20] via 172.2.1.1, Serial0/0

　　2.0.0.0/24 is subnetted, 1 subnets

　　i L1 2.2.2.0 [115/20] via 172.2.1.1, Serial0/0

　　3.0.0.0/24 is subnetted, 1 subnets

　　C 3.3.3.0 is directly connected, Loopback0

　　172.1.0.0/24 is subnetted, 1 subnets

　　i L1 172.1.1.0 [115/20] via 172.2.1.1, Serial0/0

　　172.2.0.0/24 is subnetted, 1 subnets

　　C 172.2.1.0 is directly connected, Serial0/0

　　用PING命令测试

　　r1#ping 2.2.2.2 source 1.1.1.1

　　Type escape sequence to abort.

　　Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:

　　Packet sent with a source address of 1.1.1.1

　　!!!!!

　　Success rate is 100 percent (5/5), round-trip min/avg/max = 48/126/256 ms

　　r1#ping 3.3.3.3 source 1.1.1.1

　　Type escape sequence to abort.

　　Sending 5, 100-byte ICM