双向双点重分发

steftdance

基本配置：

RT1:

routerospf 1

router-id 1.1.1.1

log-adjacency-changes

network 192.168.23.0 0.0.0.255 area 0

routerrip

version 2

network 192.168.12.0

no auto-summary

RT2:

routerrip

version 2

network 192.168.10.0

network 192.168.12.0

network 192.168.14.0

no auto-summary

RT3:

routerospf 1

router-id 3.3.3.3

log-adjacency-changes

network 192.168.23.0 0.0.0.255 area 0

network 192.168.30.0 0.0.0.255 area 0

network 192.168.34.0 0.0.0.255 area 0

RT4:

routerospf 1

router-id 4.4.4.4

log-adjacency-changes

network 192.168.34.0 0.0.0.255 area 0

routerrip

version 2

network 192.168.14.0

no auto-summary

RT1、RT2、RT3、RT4：

ints0/0     

ip ospf cost 1//设置开销和F口相同，以便形成负载均衡

查看RT1、RT2、RT3、RT4路由表：

RT1#show ip route

C    192.168.12.0/24 is directly connected,FastEthernet1/0

R    192.168.14.0/24 [120/1] via 192.168.12.2,00:00:04, FastEthernet1/0

     192.168.30.0/32 is subnetted, 1 subnets

O       192.168.30.1 [110/2] via 192.168.23.2,00:00:41, Serial0/0

R    192.168.10.0/24 [120/1] via 192.168.12.2,00:00:04, FastEthernet1/0

C    192.168.23.0/24 is directly connected,Serial0/0

O    192.168.34.0/24 [110/2] via 192.168.23.2,00:00:41, Serial0/0

RT2#showip route

C    192.168.12.0/24 is directly connected,FastEthernet1/0

C    192.168.14.0/24 is directly connected,Serial0/0

C    192.168.10.0/24 is directly connected,Loopback0

RT3#showip route

C    192.168.30.0/24 is directly connected,Loopback0

C    192.168.23.0/24 is directly connected,Serial0/0

C    192.168.34.0/24 is directly connected,FastEthernet1/0

RT4#showip route

R    192.168.12.0/24 [120/1] via 192.168.14.2,00:00:20, Serial0/0

C    192.168.14.0/24 is directly connected,Serial0/0

     192.168.30.0/32 is subnetted, 1 subnets

O       192.168.30.1 [110/2] via 192.168.34.2,00:01:39, FastEthernet1/0

R    192.168.10.0/24 [120/1] via 192.168.14.2,00:00:20, Serial0/0

O    192.168.23.0/24 [110/2] via 192.168.34.2,00:01:39, FastEthernet1/0

C    192.168.34.0/24 is directly connected,FastEthernet1/0

在RT1上将OSPF重分发进RIP

RT1：

routerrip

redistribute ospf 1 metric 3

查看RT2、RT4路由表：

RT2#show ip route

C    192.168.12.0/24 is directly connected,FastEthernet1/0

C    192.168.14.0/24 is directly connected,Serial0/0

     192.168.30.0/32 is subnetted, 1 subnets

R       192.168.30.1 [120/3]via 192.168.12.1, 00:00:13, FastEthernet1/0

C    192.168.10.0/24 is directly connected,Loopback0

R    192.168.23.0/24 [120/3]via 192.168.12.1, 00:00:13, FastEthernet1/0

R    192.168.34.0/24 [120/3]via 192.168.12.1, 00:00:13, FastEthernet1/0

RT4#showip route

R    192.168.12.0/24 [120/1] via 192.168.14.2,00:00:14, Serial0/0

C    192.168.14.0/24 is directly connected,Serial0/0

     192.168.30.0/32 is subnetted, 1 subnets

O       192.168.30.1 [110/2] via 192.168.34.2,00:07:21, FastEthernet1/0

R    192.168.10.0/24 [120/1] via 192.168.14.2,00:00:14, Serial0/0

O    192.168.23.0/24 [110/2] via 192.168.34.2,00:07:22, FastEthernet1/0

C    192.168.34.0/24 is directly connected,FastEthernet1/0

可知：RT2学习到了OSPF区域中的路由且路由正常；RT4路由表没有发生变化。

再在RT4上将OSPF重分发进RIP：

RT4：

routerrip

redistribute ospf 1 metric 3

查看RT2、RT4路由表：

RT2#show ip route

C    192.168.12.0/24 is directly connected,FastEthernet1/0

C    192.168.14.0/24 is directly connected,Serial0/0

     192.168.30.0/32 is subnetted, 1 subnets

R       192.168.30.1 [120/3] via192.168.14.1, 00:00:03, Serial0/0

                     [120/3]via 192.168.12.1, 00:00:10, FastEthernet1/0

C    192.168.10.0/24 is directly connected,Loopback0

R    192.168.23.0/24 [120/3]via 192.168.14.1, 00:00:03, Serial0/0

                     [120/3]via 192.168.12.1, 00:00:10, FastEthernet1/0

R    192.168.34.0/24 [120/3]via 192.168.14.1, 00:00:03, Serial0/0

                     [120/3] via 192.168.12.1,00:00:10, FastEthernet1/0

可知：RT2上关于OSPF区域中的路由正常，形成了负载均衡。

小结：将OSPF进RIP路由表正常，没有出现问题。

在RT1上将RIP重分发进OSPF

RT1：

routerospf 1

redistribute rip  metric 3 subnets

查看RT1、RT3、RT4路由表：

RT1(config-router)#do show ip ro

C    192.168.12.0/24 is directly connected,FastEthernet1/0

R    192.168.14.0/24 [120/1] via 192.168.12.2,00:00:07, FastEthernet1/0

     192.168.30.0/32 is subnetted, 1 subnets

O       192.168.30.1 [110/65] via 192.168.23.2,00:02:24, Serial0/0

R    192.168.10.0/24 [120/1] via 192.168.12.2,00:00:07, FastEthernet1/0

C    192.168.23.0/24 is directly connected,Serial0/0

O    192.168.34.0/24 [110/65] via 192.168.23.2,00:02:24, Serial0/0

RT3#showip route

O E2192.168.12.0/24 [110/3] via 192.168.23.1, 00:00:15, Serial0/0

O E2192.168.14.0/24 [110/3] via 192.168.23.1, 00:00:15, Serial0/0

C    192.168.30.0/24 is directly connected,Loopback0

O E2192.168.10.0/24 [110/3] via 192.168.23.1, 00:00:15, Serial0/0

C    192.168.23.0/24 is directly connected,Serial0/0

C    192.168.34.0/24 is directly connected,FastEthernet1/0

RT4(config-router)#doshow ip route

O E2 192.168.12.0/24 [110/3] via 192.168.34.2, 00:01:00,FastEthernet1/0

C    192.168.14.0/24 is directly connected,Serial0/0

     192.168.30.0/32 is subnetted, 1 subnets

O       192.168.30.1 [110/2] via 192.168.34.2,00:01:00, FastEthernet1/0

O E2 192.168.10.0/24 [110/3] via 192.168.34.2, 00:01:00,FastEthernet1/0

O    192.168.23.0/24 [110/2] via 192.168.34.2,00:01:00, FastEthernet1/0

C    192.168.34.0/24 is directly connected,FastEthernet1/0

可知：RT1路由表没有变化；RT3学习到了RIP区域的路由，且单点重分发RIP进OSPF时路由正常；RT4出现了次佳路径，192.168.10.0/24、192.168.12.0/24网段的下一跳变为了RT3。

再在RT4:上将RIP重分发进OSPF

RT4：

routerospf 1

redistribute rip metric 3 subnets

查看RT1、RT3、RT4路由表：

RT1(config-router)#do show ip ro

C    192.168.12.0/24 is directly connected,FastEthernet1/0

O E2 192.168.14.0/24 [110/3] via 192.168.23.2, 00:00:13, Serial0/0

     192.168.30.0/32 is subnetted, 1 subnets

O       192.168.30.1 [110/2] via 192.168.23.2,00:00:13, Serial0/0

R    192.168.10.0/24 [120/1] via 192.168.12.2,00:00:23, FastEthernet1/0

C    192.168.23.0/24 is directly connected,Serial0/0

O    192.168.34.0/24 [110/2] via 192.168.23.2,00:00:13, Serial0/0

RT3#showip route

O E2 192.168.12.0/24 [110/3] via 192.168.23.1, 00:00:47, Serial0/0

O E2 192.168.14.0/24 [110/3] via 192.168.34.1, 00:00:47,FastEthernet1/0

C    192.168.30.0/24 is directly connected, Loopback0

O E2 192.168.14.0/24 [110/3] via 192.168.23.1, 00:00:47, Serial0/0

C    192.168.23.0/24 is directly connected,Serial0/0

C    192.168.34.0/24 is directly connected,FastEthernet1/0

RT4(config-router)#doshow ip ro

O E2192.168.12.0/24 [110/3] via 192.168.34.2, 00:01:35, FastEthernet1/0

C    192.168.14.0/24 is directly connected,Serial0/0

     192.168.30.0/32 is subnetted, 1 subnets

O       192.168.30.1 [110/2] via 192.168.34.2,00:01:35, FastEthernet1/0

O E2192.168.10.0/24 [110/3] via 192.168.34.2, 00:01:35, FastEthernet1/0

O    192.168.23.0/24 [110/2] via 192.168.34.2,00:01:35, FastEthernet1/0

C    192.168.34.0/24 is directly connected,FastEthernet1/0

可知：RT1出现了次佳路径，192.168.10.0/24网段的下一跳变为了RT3；RT3学习到了RIP区域的路由，但路由不正常，双点重分发RIP进OSPF时RIP区域的路由没有形成负载均衡；RT4路由表较上次没有变化，依然存在次佳路径。

小结：

RIP重分发进OSPF时，OSPF的ASBR的路由表会出现次佳路径，因OSPF的AD（110）值小于RIP（120）的AD值，故当进行重分发后，会选择OSPF路由放到全局路由表中，形成了次佳路径，

而其他路由器在双点重分发时关于RIP的路由没有形成负载均衡的原因，因其中一台ASBR中的RIP路由已变成了OSPF路由，重分发时不会将该路由再进行重分发。

上例的RT3的RIP路由没有形成负载均衡即是因为RT4重分发后，192.168.10.0/24、192.168.12.0/24没有进行重分发。RT1的192.168.14.0/24也没有进行重分发。

解决方法：

修改OSPF外部AD值，使其大于RIP的AD值。

配置：

RT1、RT4：

routerospf 1

distance ospf external 130

查看RT1、RT3、RT4路由表：

RT3#show ip route

O E2 192.168.12.0/24 [110/3] via 192.168.34.1, 00:00:21,FastEthernet1/0

                     [110/3] via 192.168.23.1,00:00:21, Serial0/0

O E2 192.168.14.0/24 [110/3] via 192.168.34.1, 00:00:36,FastEthernet1/0

                     [110/3]via 192.168.23.1, 00:00:36, Serial0/0

C    192.168.30.0/24 is directly connected,Loopback0

O E2 192.168.10.0/24 [110/3] via 192.168.34.1, 00:00:36,FastEthernet1/0

                     [110/3]via 192.168.23.1, 00:00:36, Serial0/0

C    192.168.23.0/24 is directly connected,Serial0/0

C    192.168.34.0/24 is directly connected,FastEthernet1/0

RT1(config-router)#doshow ip ro                      

C    192.168.12.0/24 is directly connected,FastEthernet1/0

R    192.168.14.0/24 [120/1]via 192.168.12.2, 00:00:22, FastEthernet1/0

     192.168.30.0/32 is subnetted, 1 subnets

O       192.168.30.1 [110/2] via 192.168.23.2,00:01:36, Serial0/0

R    192.168.10.0/24 [120/1]via 192.168.12.2, 00:00:22, FastEthernet1/0

C    192.168.23.0/24 is directly connected,Serial0/0

O    192.168.34.0/24 [110/2] via 192.168.23.2,00:01:36, Serial0/0

RT4(config-router)#doshow ip ro                        

R    192.168.12.0/24 [120/1]via 192.168.14.2, 00:00:04, Serial0/0

C    192.168.14.0/24 is directly connected,Serial0/0

     192.168.30.0/32 is subnetted, 1 subnets

O       192.168.30.1 [110/2] via 192.168.34.2,00:01:14, FastEthernet1/0

R    192.168.10.0/24 [120/1]via 192.168.14.2, 00:00:04, Serial0/0

O    192.168.23.0/24 [110/2] via 192.168.34.2,00:01:14, FastEthernet1/0

C    192.168.34.0/24 is directly connected,FastEthernet1/0

可知：RT3关于RIP区域的路由形成负载均衡，RT1、RT4也没有出现次佳路径，问题已解决。

总结：

双点双向重分发时，需要注意两边路由协议进入全局路由表的优先级即AD值，AD值小的重分发进AD值大的不会出现问题，对于AD值大的重分发进AD值小的情况，应修改AD值，使其不会出现次佳路径等问题。还需注意的是：外部AD值、内部AD值，以及重分发的顺序问题。