不同协议之间的路由，是不会相互交换的。

一、路由重发布的意义：

1、把一种协议的路由注入到另一种协议当中，譬如把RIP的路由注入到OSPF当中

2、把同一种路由协议的一个进程注入到另一个进程中，譬如把OSPF的进程31注入到32当中

二、重发布需要考虑的问题：

1、只有在路由表中的路由才可以被重分发

2、路由回馈问题

首先，R4是可以通过RIP学习到192.168.1.0这个网段的路由。如果在R3上把1.0这段路由重发布到OSPF当中的话，R4又会通过OSPF学习到这段路由：R4---R2---R1---R3--R5。那么根据AD值越小越优先的原则，R4就会选择从OSPF（110）中学到的路由作为最优路径。因此，实际R4获取到的是次优路径。

3、度量值（metric）不一致的问题

不同的协议对于metric的理解是不一样的。譬如，RIP是以hop作为metric值；OSPF是以cost作为metric值。

1）重分发的时候可以指定注入后的路由的metric值

redistribute metric 20

2）或者不指定，使用默认值（种子度量值）

default metric

4、收敛时间不一致的问题

三、实验汇总：

1、不同协议路由之间的重分发

R1#show ip route
C 192.168.12.0/24 is directly connected, FastEthernet0/0
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0

R2#show ip route
C 192.168.12.0/24 is directly connected, FastEthernet1/0
R 1.0.0.0/8 [120/1] via 192.168.12.1, 00:00:00, FastEthernet1/0
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [110/2] via 192.168.23.3, 00:18:56, FastEthernet0/0
C 192.168.23.0/24 is directly connected, FastEthernet0/0

R3#show ip route
2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/2] via 192.168.23.2, 00:08:14, FastEthernet0/0
3.0.0.0/32 is subnetted, 1 subnets
C 3.3.3.3 is directly connected, Loopback0
C 192.168.23.0/24 is directly connected, FastEthernet0/0

R2配置路由重分发以后：

R2(config)#router ospf 1
R2(config-router)#redistribute rip subnets

#subnets:把rip的所有子网路由也注入到ospf当中，没有定义metric，则用默认的20

R3#show ip route
O E2 192.168.12.0/24 [110/20] via 192.168.23.2, 00:00:20, FastEthernet0/0
O E2 1.0.0.0/8 [110/20] via 192.168.23.2, 00:00:20, FastEthernet0/0
2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/2] via 192.168.23.2, 00:00:20, FastEthernet0/0
3.0.0.0/32 is subnetted, 1 subnets
C 3.3.3.3 is directly connected, Loopback0
C 192.168.23.0/24 is directly connected, FastEthernet0/0

-----------------------------------------------

R2(config)#router rip
R2(config-router)#redistribute ospf 1

R1#show ip route
C 192.168.12.0/24 is directly connected, FastEthernet0/0
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0

R1依旧没有学习到OSPF的路由，因为R2注入OSPF路由时没有指定metric，根据种子度量值，metric为0，无穷大，所以没有被写入R1的路由表当中

R2(config-router)#redistribute ospf 1 metric 5

R1#show ip route
C 192.168.12.0/24 is directly connected, FastEthernet0/0
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
R 2.0.0.0/8 [120/5] via 192.168.12.2, 00:00:04, FastEthernet0/0
R 3.0.0.0/8 [120/5] via 192.168.12.2, 00:00:04, FastEthernet0/0
R 192.168.23.0/24 [120/5] via 192.168.12.2, 00:00:04, FastEthernet0/0

2、直连路由重分发

R3的loopback0不要宣告进OSPF，而是在R3上重分发直连路由，R2也一样可以学习到.3的路由

R3(config)#router ospf 1
R3(config-router)#redistribute connected subnets metric 30

R2#show ip route
C 192.168.12.0/24 is directly connected, FastEthernet1/0
R 1.0.0.0/8 [120/1] via 192.168.12.1, 00:00:10, FastEthernet1/0
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O E2 3.3.3.3 [110/30] via 192.168.23.3, 00:01:27, FastEthernet0/0
C 192.168.23.0/24 is directly connected, FastEthernet0/0

3、静态路由重分发

R1 R2不要运行RIP，R2写一条静态路由指向.1网段，然后R2把静态路由重分发进OSPF，R3就可以学习到.1的网段了

R2(config)#ip route 1.1.1.0 255.255.255.0 192.168.12.1
R2(config)#router ospf 1
R2(config-router)#redistribute static subnets

R3#show ip route
1.0.0.0/24 is subnetted, 1 subnets
O E2 1.1.1.0 [110/20] via 192.168.23.2, 00:00:03, FastEthernet0/0
2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/2] via 192.168.23.2, 00:14:04, FastEthernet0/0
3.0.0.0/32 is subnetted, 1 subnets
C 3.3.3.3 is directly connected, Loopback0
C 192.168.23.0/24 is directly connected, FastEthernet0/0