路由重发布相关知识
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
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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
CCIE - 重分发路由控制（Tag过滤）
R2:
route-map RIP_TO_OSPF deny 10
match tag 110
!
route-map RIP_TO_OSPF permit 20
set tag 120
!
router ospf 1
redistribute rip subnets route-map RIP_TO_OSPF
!
route-map OSPF_TO_RIP deny 10
match tag 120
!
route-map OSPF_TO_RIP permit 20
set tag 110
!
router rip
redistribute ospf 1 metric 1 route-map OSPF_TO_RIP
在双向重分布时，将OSPF自己的路由打上Tag 110，将RIP自己的路由打上Tag 120，并且通过匹配Tag拒绝原本属于自己的路由再返回，也就是OSPF重分布进RIP时，拒绝Tag为120的路由返回，RIP重分布进OSPF时，拒绝Tag为110的路由返回，因为它们原本就是自己的路由。
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R4:
route-map RIP_TO_OSPF deny 10
match tag 110
!
route-map RIP_TO_OSPF permit 20
set tag 120
!
router ospf 1
redistribute rip subnets route-map RIP_TO_OSPF
!
route-map OSPF_TO_RIP deny 10
match tag 120
!
route-map OSPF_TO_RIP permit 20
set tag 110
!
router rip
redistribute ospf 1 metric 1 route-map OSPF_TO_RIP
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R5#sh ip route 100.1.1.0
Routing entry for 100.1.1.0/24
Known via "ospf 1", distance 110, metric 20
Tag 120, type extern 2, forward metric 1
Last update from 45.1.1.4 on FastEthernet1/0, 00:20:20 ago
Routing Descriptor Blocks:
* 45.1.1.4, from 45.1.1.4, 00:20:20 ago, via FastEthernet1/0
Route metric is 20, traffic share count is 1
Route tag 120