ip default-network 在RIP协议中要注意的问题[文档] 默认路由系列文档3/5
2007-03-28
实验设计：
配置:
R1#show run
Building configuration...
Current configuration : 901 bytes
!
version 12.3
!
hostname R1
!
interface Loopback0
ip address 1.1.1.1 255.255.255.0
!
interface FastEthernet0/0
ip address 112.1.1.1 255.255.255.0
!
end
--------------------------------------------------------------------
R2#show run
Building configuration...
Current configuration : 939 bytes
!
version 12.3
!
hostname R2
!
interface Loopback0
ip address 2.2.2.2 255.255.255.0
!
interface FastEthernet0/0
ip address 112.1.1.2 255.255.255.0
!
interface Serial1/1
ip address 23.1.1.2 255.255.255.0
!
end
-----------------------------------------------------------------------
R3#show run
Building configuration...
Current configuration : 900 bytes
!
version 12.3
!
hostname R3
!
interface Loopback0
ip address 3.3.3.3 255.255.255.0
!
interface Serial1/0
ip address 23.1.1.3 255.255.255.0
!
end
-------------------------------------------------------------
1、R2(config)#ip default-network 23.1.1.0
R2#show ip ro
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 23.1.1.3 to network 10.0.0.0
2.0.0.0/24 is subnetted, 1 subnets
C 2.2.2.0 is directly connected, Loopback0
23.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 23.1.1.0/24 is directly connected, Serial1/1
S 23.0.0.0/8 [1/0] via 23.1.1.0
112.0.0.0/24 is subnetted, 1 subnets
C 112.1.1.0 is directly connected, FastEthernet0/0
出现了一条静态路由
我们看看配置文件
R2#show run
Building configuration...
Current configuration : 948 bytes
!
version 12.3
!
hostname R2
!
.
.
.
!
ip route 23.0.0.0 255.0.0.0 23.1.1.0
!
end
出现了一条奇怪的静态路由，尤其是下一条地址怎么可能是X.X.X.0呢。
说明ip default-network后面之可以接主类网络的网络号
删除掉上面的配置
R2(config)#no ip route 23.0.0.0 255.0.0.0 23.1.1.0
%No matching route to delete //报错
R2(config)#no ip default-network 23.1.1.0
可以(与实验手册的实验结果不同,可能是IOS版本的原因)
附：本文档实验环境
IOS (tm) 7200 Software (C7200-JK9SU2-M), Version 12.3(16a), RELEASE SOFTWARE (fc2)
2、
R2(config)#ip default-network 23.0.0.0
R2#show run
Building configuration...
Current configuration : 939 bytes
!
version 12.3
!
hostname R2
!
.
.
.
!
ip default-network 23.0.0.0
!
end
R2#show ip ro
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
2.0.0.0/24 is subnetted, 1 subnets
C 2.2.2.0 is directly connected, Loopback0
* 23.0.0.0/24 is subnetted, 1 subnets
C 23.1.1.0 is directly connected, Serial1/1
112.0.0.0/24 is subnetted, 1 subnets
C 112.1.1.0 is directly connected, FastEthernet0/0
R2#ping 3.3.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
路由表中有了星号的默认路由，但无法到达R3的环回口
3、R2(config)#router
rip
R2(config-router)#net 112.0.0.0
R1(config)#router rip
R1(config-router)#net 112.0.0.0
R1#show ip ro
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 112.1.1.2 to network 0.0.0.0
1.0.0.0/24 is subnetted, 1 subnets
C 1.1.1.0 is directly connected, Loopback0
112.0.0.0/24 is subnetted, 1 subnets
C 112.1.1.0 is directly connected, FastEthernet0/0
R* 0.0.0.0/0 [120/1] via 112.1.1.2, 00:00:09, FastEthernet0/0
对于这种没有对应接口的默认路由，RIP会通告一条0.0.0.0/0的路由条目出去
R1#ping 23.1.1.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 23.1.1.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 32/68/132 ms
4、
R2(config)#no ip default-network 23.0.0.0
R2(config)#ip default-network 10.0.0.0
R2(config)#ip route 10.0.0.0 255.0.0.0 23.1.1.3
R2#show ip ro
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 23.1.1.3 to network 10.0.0.0
2.0.0.0/24 is subnetted, 1 subnets
C 2.2.2.0 is directly connected, Loopback0
23.0.0.0/24 is subnetted, 1 subnets
C 23.1.1.0 is directly connected, Serial1/1
112.0.0.0/24 is subnetted, 1 subnets
C 112.1.1.0 is directly connected, FastEthernet0/0
S* 10.0.0.0/8 [1/0] via 23.1.1.3
R2#ping 3.3.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 28/54/100 ms
默认路由有了对应的端口，R2 的任何未知路由都会发到这个端口
R1#show ip ro
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
112.0.0.0/24 is subnetted, 1 subnets
C 112.1.1.0 is directly connected, FastEthernet0/0
此时R2不会发送0.0.0.0/0的默认路由了
总结：
1、ip default-network 后面接的网络地址要求是主类网络号
2、不手动加静态路由的时候，默认路由没有对应端口。RIP会通告出0.0.0.0/0的默认路由。
注意：此时 ip default-network 后面的网络地址必须在路由表中有，否则不起作用；但是具体是哪个地址，效果一样。也就是说这个地址没有实际作用，该路有并不可以ping到外部路由的环回口地址。
3、手动加上该主类网络的静态路由时，默认路由就有了对应端口，此时该
路由器就可以ping外部
路由器的环回口地址了。
对于ip default-network 在EIGRP协议中的应用请见
《ip default-network 在EIGRP协议中的应用[文档] 默认路由系列文档4/5》
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