1、网络拓扑
2、第三种方式配置默认路由（接口下汇总的方式）
R3# R3#config t Enter configuration commands, one per line. End with CNTL/Z. R3(config)#interface s1/0 R3(config-if)#ip summary-address eigrp 100 0.0.0.0 0.0.0.0 R3(config-if)#end 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 0.0.0.0 to network 0.0.0.0 1.0.0.0/24 is subnetted, 1 subnets D 1.1.1.0 [90/2300416] via 192.168.23.1, 00:00:05, Serial1/0 3.0.0.0/24 is subnetted, 1 subnets C 3.3.3.0 is directly connected, Loopback0 172.16.0.0/24 is subnetted, 1 subnets D 172.16.12.0 [90/2172416] via 192.168.23.1, 00:00:05, Serial1/0 C 192.168.23.0/24 is directly connected, Serial1/0 D* 0.0.0.0/0 is a summary, 00:00:05, Null0 R3# R2# R2#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 192.168.23.2 to network 0.0.0.0 1.0.0.0/24 is subnetted, 1 subnets D 1.1.1.0 [90/156160] via 172.16.12.1, 02:26:25, FastEthernet0/0 172.16.0.0/24 is subnetted, 1 subnets C 172.16.12.0 is directly connected, FastEthernet0/0 C 192.168.23.0/24 is directly connected, Serial1/0 D* 0.0.0.0/0 [90/2297856] via 192.168.23.2, 00:00:26, Serial1/0 R2# R1# R1#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 172.16.12.2 to network 0.0.0.0 1.0.0.0/24 is subnetted, 1 subnets C 1.1.1.0 is directly connected, Loopback0 172.16.0.0/24 is subnetted, 1 subnets C 172.16.12.0 is directly connected, FastEthernet0/0 D 192.168.23.0/24 [90/2172416] via 172.16.12.2, 02:26:47, FastEthernet0/0 D* 0.0.0.0/0 [90/2300416] via 172.16.12.2, 00:00:40, FastEthernet0/0 R1#
3、第四种方式配置默认路由（特定路由的默认路由）
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 D 1.1.1.0 [90/2300416] via 192.168.23.1, 00:00:39, Serial1/0 3.0.0.0/24 is subnetted, 1 subnets C 3.3.3.0 is directly connected, Loopback0 172.16.0.0/24 is subnetted, 1 subnets D 172.16.12.0 [90/2172416] via 192.168.23.1, 00:00:39, Serial1/0 C 192.168.23.0/24 is directly connected, Serial1/0 R3#config t Enter configuration commands, one per line. End with CNTL/Z. R3(config)#interface loopback 33 R3(config-if)#ip add 33.0.0.33 255.0.0.0 R3(config-if)#no shutdown R3(config-if)#exit R3(config)#router eigrp 100 R3(config-router)#network 33.0.0.33 0.0.0.0 R3(config-router)#end R3#show ip *Nov 25 13:04:08.023: %SYS-5-CONFIG_I: Configured from console by console 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 D 1.1.1.0 [90/2300416] via 192.168.23.1, 00:01:42, Serial1/0 C 33.0.0.0/8 is directly connected, Loopback33 3.0.0.0/24 is subnetted, 1 subnets C 3.3.3.0 is directly connected, Loopback0 172.16.0.0/24 is subnetted, 1 subnets D 172.16.12.0 [90/2172416] via 192.168.23.1, 00:01:42, Serial1/0 C 192.168.23.0/24 is directly connected, Serial1/0 R3# R3#config t Enter configuration commands, one per line. End with CNTL/Z. R3(config)#ip default-network 33.0.0.0 R3(config)#end R3#shiw *Nov 25 13:06:15.331: %SYS-5-CONFIG_I: Configured from console by console 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 D 1.1.1.0 [90/2300416] via 192.168.23.1, 00:03:49, Serial1/0 C* 33.0.0.0/8 is directly connected, Loopback33 3.0.0.0/24 is subnetted, 1 subnets C 3.3.3.0 is directly connected, Loopback0 172.16.0.0/24 is subnetted, 1 subnets D 172.16.12.0 [90/2172416] via 192.168.23.1, 00:03:49, Serial1/0 C 192.168.23.0/24 is directly connected, Serial1/0 R3# R2#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 D 1.1.1.0 [90/156160] via 172.16.12.1, 02:41:09, FastEthernet0/0 D 33.0.0.0/8 [90/2297856] via 192.168.23.2, 00:00:19, Serial1/0 3.0.0.0/24 is subnetted, 1 subnets D 3.3.3.0 [90/2297856] via 192.168.23.2, 00:01:53, Serial1/0 172.16.0.0/24 is subnetted, 1 subnets C 172.16.12.0 is directly connected, FastEthernet0/0 C 192.168.23.0/24 is directly connected, Serial1/0 R2# R2# R2# R2#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 192.168.23.2 to network 33.0.0.0 1.0.0.0/24 is subnetted, 1 subnets D 1.1.1.0 [90/156160] via 172.16.12.1, 02:43:41, FastEthernet0/0 D* 33.0.0.0/8 [90/2297856] via 192.168.23.2, 00:00:42, Serial1/0 3.0.0.0/24 is subnetted, 1 subnets D 3.3.3.0 [90/2297856] via 192.168.23.2, 00:04:24, Serial1/0 172.16.0.0/24 is subnetted, 1 subnets C 172.16.12.0 is directly connected, FastEthernet0/0 C 192.168.23.0/24 is directly connected, Serial1/0 R2# R1#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 C 1.1.1.0 is directly connected, Loopback0 3.0.0.0/24 is subnetted, 1 subnets D 3.3.3.0 [90/2300416] via 172.16.12.2, 00:00:03, FastEthernet0/0 172.16.0.0/24 is subnetted, 1 subnets C 172.16.12.0 is directly connected, FastEthernet0/0 D 192.168.23.0/24 [90/2172416] via 172.16.12.2, 02:39:28, FastEthernet0/0 R1# R1# R1# R1#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 172.16.12.2 to network 33.0.0.0 1.0.0.0/24 is subnetted, 1 subnets C 1.1.1.0 is directly connected, Loopback0 D* 33.0.0.0/8 [90/2300416] via 172.16.12.2, 00:01:11, FastEthernet0/0 3.0.0.0/24 is subnetted, 1 subnets D 3.3.3.0 [90/2300416] via 172.16.12.2, 00:04:53, FastEthernet0/0 172.16.0.0/24 is subnetted, 1 subnets C 172.16.12.0 is directly connected, FastEthernet0/0 D 192.168.23.0/24 [90/2172416] via 172.16.12.2, 02:44:18, FastEthernet0/0 R1#
原文地址：http://www.cnblogs.com/leishu/p/16924995.html
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