在自己的2501上研究这三种默认路由的区别. 指定默认路由（last resort gateway）的指令供有3种，可以分成两类： 1、ip default-gateway 当路由器上的ip routing无效时，使用它指定默认路由，用于RXBoot模式（no ip routing）下安装IOS等。或者关闭ip routing 让路由器当主机用,此时需要配置默认网关 2、ip default-network和ip route 0.0.0.0 0.0.0.0 两者都用于ip routing有效的路由器上，区别主要在于路由协议是否传播这条路由信息。比如：IGRP无法识别0.0.0.0，因此传播默认路由时必须用ip default-network。 当用ip default-network指令设定多条默认路由时，administrative distance最短的成为最终的默认路由；如果有复数条路由distance值相等，那么在路由表（show ip route）中靠上的成为默认路由。 同时使用ip default-network和ip route 0.0.0.0 0.0.0.0双方设定默认路由时，如果ip default-network设定的网络是直连（静态、且已知）的，那么它就成为默认路由；如果ip default-network指定的网络是由交换路由信息得来的，则ip route 0.0.0.0 0.0.0.0指定的表项成为默认路由。 最后，如果使用多条ip route 0.0.0.0 0.0.0.0指令，则流量会自动在多条链路上负载均衡。 官方详细文档点这里 例子: 关闭ip routing 举例: mycisco(config)#no ip routing mycisco(config)#ip default-gateway 192.168.0.1 mycisco(config)#end mycisco#ping www.flashku.com Type escape sequence to abort. Sending 5, 100-byte ICMP Echoes to 61.152.167.75, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 60/60/60 ms mycisco#show ip route Default gateway is 192.168.0.1 Host               Gateway           Last Use    Total Uses  Interface ICMP redirect cache is empty mycisco# ip route例子: ip route 0.0.0.0 0.0.0.0 192.168.0.1 mycisco#ping www.flashku.com Type escape sequence to abort. Sending 5, 100-byte ICMP Echoes to 61.152.167.75, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 56/56/60 ms mycisco#show 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        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route Gateway of last resort is 192.168.0.1 to network 0.0.0.0 C    1.0.0.0/8 is directly connected, Loopback0 C    192.168.0.0/24 is directly connected, Ethernet0 S*   0.0.0.0/0 [1/0] via 192.168.0.1 mycisco# ip default-network 必须是在所到网络已经存在路由的情况下,否则执行无效. mycisco(config)#ip route 61.0.0.0 255.0.0.0 192.168.0.1 mycisco#show 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        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route Gateway of last resort is not set C    1.0.0.0/8 is directly connected, Loopback0 S    61.0.0.0/8 [1/0] via 192.168.0.1 C    192.168.0.0/24 is directly connected, Ethernet0 接着我们执行: mycisco(config)#ip default-network 61.0.0.0 再看路由表: mycisco#show 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        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route Gateway of last resort is 192.168.0.1 to network 61.0.0.0 C    1.0.0.0/8 is directly connected, Loopback0 S*   61.0.0.0/8 [1/0] via 192.168.0.1 C    192.168.0.0/24 is directly connected, Ethernet0 文章录入：csh    责任编辑：csh