2024年5月8日发(作者：手机音乐格式转换器)

缺省网关和默认路由的区别

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。

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

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

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

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补充：

-默认路由用于把数据包转发到不在路由表里的地址中

-在那些不需要完整的路由信息的地方，比如STUB区域，默认路由可以减少内存使用并降

低CPU的开销