CCNP13-双点双向重发布_双点双向重发布 offset-list-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_36148336/article/details/104391900

拓扑图
在这里插入图片描述
R1、R2、R4之间运行rip，其中R2的环回在rip中
R2、R3、R4之间运行ospf，其中R4的环回在ospf中
在R2和R4路由器中做双向重发布，并且将ospf重发布进rip时指定种子度量值为1，重发布的顺序为：R2：rip··>ospf R4：ospf··>rip R4：rip··>ospf R2：ospf··>rip此图构成双点双向重发布。
双点双向重发布（rip和ospf之间）会产生两个问题：
1，路由回馈
3，选路不佳
R1路由表

R1#sho ip route rip 
     34.0.0.0/24 is subnetted, 1 subnets
R       34.1.1.0 [120/1] via 14.1.1.1, 00:00:27, Serial1/0
                 [120/1] via 12.1.1.2, 00:00:20, Serial1/1
     2.0.0.0/24 is subnetted, 1 subnets
R       2.2.2.0 [120/1] via 14.1.1.1, 00:00:27, Serial1/0
                [120/1] via 12.1.1.2, 00:00:20, Serial1/1
     3.0.0.0/24 is subnetted, 1 subnets
R       3.3.3.0 [120/1] via 14.1.1.1, 00:00:27, Serial1/0
                [120/1] via 12.1.1.2, 00:00:20, Serial1/1
     4.0.0.0/24 is subnetted, 1 subnets
R       4.4.4.0 [120/1] via 14.1.1.1, 00:00:27, Serial1/0
                [120/1] via 12.1.1.2, 00:00:20, Serial1/1
     23.0.0.0/24 is subnetted, 1 subnets
R       23.1.1.0 [120/1] via 14.1.1.1, 00:00:27, Serial1/0
                 [120/1] via 12.1.1.2, 00:00:20, Serial1/1

R1到达所有网段全部负载均衡，这显然不正确。
R1到达3.3.3.0/24应该负载均衡才是正确的。
比如R1到达2.2.2.0/24网段负载均衡，走12.1.1.2没问题（通过rip学习到metric值为1），但是不能走14.1.1.1，这是因为，R2将2.2.2.0/24这条路由重发布进ospf，R4又将这条路由重发布进rip，由于重发布时种子度量值为1，AD值相同，R1通过R2和R4学习到的这条路由metric值一样，所以负载均衡。
其他网段负载均衡也是一样的原因。这就是路由回馈现象，属于rip的路由重发布进ospf，又被ospf重发布回到rip，路由回馈导致的选路不佳。

R4的路由表

R4#sho ip route 
     34.0.0.0/24 is subnetted, 1 subnets
C       34.1.1.0 is directly connected, Serial1/0
     1.0.0.0/24 is subnetted, 1 subnets
O E2    1.1.1.0 [110/20] via 34.1.1.1, 00:39:41, Serial1/0
     2.0.0.0/24 is subnetted, 1 subnets
O E2    2.2.2.0 [110/20] via 34.1.1.1, 00:39:41, Serial1/0
     3.0.0.0/24 is subnetted, 1 subnets
O       3.3.3.0 [110/65] via 34.1.1.1, 00:40:39, Serial1/0
     4.0.0.0/24 is subnetted, 1 subnets
C       4.4.4.0 is directly connected, Loopback0
     23.0.0.0/24 is subnetted, 1 subnets
O       23.1.1.0 [110/128] via 34.1.1.1, 00:40:39, Serial1/0
     12.0.0.0/24 is subnetted, 1 subnets
O E2    12.1.1.0 [110/20] via 34.1.1.1, 00:39:42, Serial1/0
     14.0.0.0/24 is subnetted, 1 subnets
C       14.1.1.0 is directly connected, Serial1/1

R4通过ospf学习到的三条OE2路由本应该通过rip学习才是正确的，这是因为通过rip学习到的这三条路由AD值为120，而这三条路由被R2重发布进ospf时AD值为110，故R4优选了ospf的路由，从而导致的选路不佳，那么只要让R4学到的这三条路由AD大于120，那么R4就不会优选ospf的路由。

R4(config)#access-list 1 permit 1.1.1.0	//通过acl抓取到这三条路由
R4(config)#access-list 1 permit 2.2.2.0
R4(config)#access-list 1 permit 12.1.1.0
R4(config-router)#distance 121 92.2.2.2 0.0.0.0 1	//把R2传给我的三条路由AD值改为121

此时查看R4的路由表

R4#sho ip route 
     34.0.0.0/24 is subnetted, 1 subnets
C       34.1.1.0 is directly connected, Serial1/0
     1.0.0.0/24 is subnetted, 1 subnets
R       1.1.1.0 [120/1] via 14.1.1.2, 00:00:18, Serial1/1
     2.0.0.0/24 is subnetted, 1 subnets
O E2    2.2.2.0 [121/20] via 34.1.1.1, 00:03:14, Serial1/0
     3.0.0.0/24 is subnetted, 1 subnets
O       3.3.3.0 [110/65] via 34.1.1.1, 00:03:14, Serial1/0
     4.0.0.0/24 is subnetted, 1 subnets
C       4.4.4.0 is directly connected, Loopback0
     23.0.0.0/24 is subnetted, 1 subnets
O       23.1.1.0 [110/128] via 34.1.1.1, 00:03:14, Serial1/0
     12.0.0.0/24 is subnetted, 1 subnets
R       12.1.1.0 [120/1] via 14.1.1.2, 00:00:18, Serial1/1
     14.0.0.0/24 is subnetted, 1 subnets
C       14.1.1.0 is directly connected, Serial1/1

发现2.2.2.0/24还是没改过来，这是因为R1没有给R4传递这条路由，所以R4只能通过ospf学习这条路由，为什么R1不给R4传递这条路由了呢？R1通过rip学习到metric值为1，R4把这条路由重发布给rip，metric值也为1，所以R1负载均衡，由于水平分割机制，R1不会把这条路由在传回给R2和R4。
那么就把这条路由在R4上重发布给rip时的metric值增大即可。

R4(config)#access-list 2 permit 2.2.2.0
R4(config)#route-map c1 permit 10
R4(config-route-map)#match ip address 2
R4(config-route-map)#set metric 3
R4(config-route-map)#exi
R4(config)#route-map c1 permit 20
R4(config-route-map)#exi
R4(config)#router rip 
R4(config-router)#redistribute ospf 100 metric 1 route-map c1
R4(config-router)#en
R4#sho ip route 
     34.0.0.0/24 is subnetted, 1 subnets
C       34.1.1.0 is directly connected, Serial1/0
     1.0.0.0/24 is subnetted, 1 subnets
R       1.1.1.0 [120/1] via 14.1.1.2, 00:00:05, Serial1/1
     2.0.0.0/24 is subnetted, 1 subnets
R       2.2.2.0 [120/2] via 14.1.1.2, 00:00:05, Serial1/1
     3.0.0.0/24 is subnetted, 1 subnets
O       3.3.3.0 [110/65] via 34.1.1.1, 00:15:06, Serial1/0
     4.0.0.0/24 is subnetted, 1 subnets
C       4.4.4.0 is directly connected, Loopback0
     23.0.0.0/24 is subnetted, 1 subnets
O       23.1.1.0 [110/128] via 34.1.1.1, 00:15:06, Serial1/0
     12.0.0.0/24 is subnetted, 1 subnets
R       12.1.1.0 [120/1] via 14.1.1.2, 00:00:06, Serial1/1
     14.0.0.0/24 is subnetted, 1 subnets
C       14.1.1.0 is directly connected, Serial1/1

此时R4路由表正常
看R2的路由表

R2#sho ip route 
     34.0.0.0/24 is subnetted, 1 subnets
O       34.1.1.0 [110/128] via 23.1.1.2, 01:35:33, Serial1/1
     1.0.0.0/24 is subnetted, 1 subnets
O E2    1.1.1.0 [110/20] via 23.1.1.2, 00:17:55, Serial1/1
     2.0.0.0/24 is subnetted, 1 subnets
C       2.2.2.0 is directly connected, Loopback0
     3.0.0.0/24 is subnetted, 1 subnets
O       3.3.3.0 [110/65] via 23.1.1.2, 01:33:29, Serial1/1
     4.0.0.0/24 is subnetted, 1 subnets
O       4.4.4.0 [110/129] via 23.1.1.2, 01:33:19, Serial1/1
     23.0.0.0/24 is subnetted, 1 subnets
C       23.1.1.0 is directly connected, Serial1/1
     12.0.0.0/24 is subnetted, 1 subnets
C       12.1.1.0 is directly connected, Serial1/0
     14.0.0.0/24 is subnetted, 1 subnets
O E2    14.1.1.0 [110/20] via 23.1.1.2, 01:31:33, Serial1/1

同样的问题，R2学习AD值为110的ospf路由，不学习AD值为120的rip路由

R2(config)#access-list 1 permit 1.1.1.0
R2(config)#access-list 1 permit 14.1.1.0
R2(config)#router ospf 100
R2(config-router)#distance 121 94.4.4.4 0.0.0.0 1
R2(config-router)#en
R2#sho ip route 
     34.0.0.0/24 is subnetted, 1 subnets
O       34.1.1.0 [110/128] via 23.1.1.2, 00:00:26, Serial1/1
     1.0.0.0/24 is subnetted, 1 subnets
R       1.1.1.0 [120/1] via 12.1.1.1, 00:00:11, Serial1/0
     2.0.0.0/24 is subnetted, 1 subnets
C       2.2.2.0 is directly connected, Loopback0
     3.0.0.0/24 is subnetted, 1 subnets
O       3.3.3.0 [110/65] via 23.1.1.2, 00:00:26, Serial1/1
     4.0.0.0/24 is subnetted, 1 subnets
O       4.4.4.0 [110/129] via 23.1.1.2, 00:00:26, Serial1/1
     23.0.0.0/24 is subnetted, 1 subnets
C       23.1.1.0 is directly connected, Serial1/1
     12.0.0.0/24 is subnetted, 1 subnets
C       12.1.1.0 is directly connected, Serial1/0
     14.0.0.0/24 is subnetted, 1 subnets
R       14.1.1.0 [120/1] via 12.1.1.1, 00:00:12, Serial1/0

此时R4的路由已经正常
看R1的路由表

R1#sho ip route 
     34.0.0.0/24 is subnetted, 1 subnets
R       34.1.1.0 [120/1] via 14.1.1.1, 00:00:17, Serial1/0
                 [120/1] via 12.1.1.2, 00:00:14, Serial1/1
     1.0.0.0/24 is subnetted, 1 subnets
C       1.1.1.0 is directly connected, Loopback0
     2.0.0.0/24 is subnetted, 1 subnets
R       2.2.2.0 [120/1] via 12.1.1.2, 00:00:14, Serial1/1
     3.0.0.0/24 is subnetted, 1 subnets
R       3.3.3.0 [120/1] via 14.1.1.1, 00:00:17, Serial1/0
                [120/1] via 12.1.1.2, 00:00:14, Serial1/1
     4.0.0.0/24 is subnetted, 1 subnets
R       4.4.4.0 [120/1] via 14.1.1.1, 00:00:17, Serial1/0
                [120/1] via 12.1.1.2, 00:00:14, Serial1/1
     23.0.0.0/24 is subnetted, 1 subnets
R       23.1.1.0 [120/1] via 14.1.1.1, 00:00:18, Serial1/0
                 [120/1] via 12.1.1.2, 00:00:15, Serial1/1
     12.0.0.0/24 is subnetted, 1 subnets
C       12.1.1.0 is directly connected, Serial1/1
     14.0.0.0/24 is subnetted, 1 subnets
C       14.1.1.0 is directly connected, Serial1/0

34.1.1.0/24、4.4.4.0/24、23.1.1.0/24这三条路由，在R2和R4重发布进rip时种子度量值都为1，故R1负载均衡，只需在R2上把重发布进rip的34.1.1.0/24、4.4.4.0/24路由的metric增大，把R4上重发布进rip的23.1.1.0/24路由metric值增大即可。这里使用offset-list

R1(config)#access-list 1 permit 34.1.1.0
R1(config)#access-list 1 permit 4.4.4.0
R1(config)#access-list 2 permit 23.1.1.0
R1(config)#router rip 
R1(config-router)#offset-list 1 in 3 serial 1/1
R1(config-router)#offset-list 2 in 3 serial 1/0
R1#sho ip route rip 
     34.0.0.0/24 is subnetted, 1 subnets
R       34.1.1.0 [120/1] via 14.1.1.1, 00:00:07, Serial1/0
     2.0.0.0/24 is subnetted, 1 subnets
R       2.2.2.0 [120/1] via 12.1.1.2, 00:00:17, Serial1/1
     3.0.0.0/24 is subnetted, 1 subnets
R       3.3.3.0 [120/1] via 14.1.1.1, 00:00:07, Serial1/0
                [120/1] via 12.1.1.2, 00:00:17, Serial1/1
     4.0.0.0/24 is subnetted, 1 subnets
R       4.4.4.0 [120/1] via 14.1.1.1, 00:00:07, Serial1/0
     23.0.0.0/24 is subnetted, 1 subnets
R       23.1.1.0 [120/1] via 12.1.1.2, 00:00:17, Serial1/1

此时R1路由表正常
看R3路由表

R3#sho ip route ospf 
     1.0.0.0/24 is subnetted, 1 subnets
O E2    1.1.1.0 [110/20] via 34.1.1.2, 00:35:22, Serial1/1
                [110/20] via 23.1.1.1, 00:14:11, Serial1/0
     2.0.0.0/24 is subnetted, 1 subnets
O E2    2.2.2.0 [110/20] via 34.1.1.2, 00:20:33, Serial1/1
                [110/20] via 23.1.1.1, 01:49:49, Serial1/0
     4.0.0.0/24 is subnetted, 1 subnets
O       4.4.4.0 [110/65] via 34.1.1.2, 01:50:47, Serial1/1
     12.0.0.0/24 is subnetted, 1 subnets
O E2    12.1.1.0 [110/20] via 34.1.1.2, 00:35:22, Serial1/1
                 [110/20] via 23.1.1.1, 01:49:49, Serial1/0
     14.0.0.0/24 is subnetted, 1 subnets
O E2    14.1.1.0 [110/20] via 34.1.1.2, 01:49:00, Serial1/1
                 [110/20] via 23.1.1.1, 00:14:11, Serial1/0

R3到达2.2.2.0/24、12.1.1.0/24、14.1.1.0/24网段负载均衡，因为R2和R4重发布进ospf时AD值都为110，故负载均衡，但ospf中一个路由器学习到两条相同AD值的路由，不能通过修改AD值来优选路由
我们知道OE1类型优于OE2，metric值小优，故我们在R2上把2.2.2.0/24、12.1.1.0/24重发布时类型改为OE1，R3优选R2的这两条路由，把14.1.1.0/24metric值改为21，R3优选R4的这条路由

R2(config)#access-list 2 permit 2.2.2.0
R2(config)#access-list 2 permit 12.1.1.0
R2(config)#access-list 3 permit 14.1.1.0
R2(config)#route-map c2 permit 10
R2(config-route-map)#match ip address 2
R2(config-route-map)#set metric-type type-1
R2(config-route-map)#exi
R2(config)#route-map c2 permit 20
R2(config-route-map)#match ip address 3
R2(config-route-map)#set metric 21
R2(config-route-map)#exi
R2(config)#route-map c2 permit 30
R2(config-route-map)#exi
R2(config)#router ospf 100
R2(config-router)#redistribute rip subnets route-map c2

此时R3的路由表已经正常

R3#sho ip route ospf 
     1.0.0.0/24 is subnetted, 1 subnets
O E2    1.1.1.0 [110/20] via 34.1.1.2, 00:57:22, Serial1/1
                [110/20] via 23.1.1.1, 00:36:10, Serial1/0
     2.0.0.0/24 is subnetted, 1 subnets
O E1    2.2.2.0 [110/84] via 23.1.1.1, 00:00:06, Serial1/0
     4.0.0.0/24 is subnetted, 1 subnets
O       4.4.4.0 [110/65] via 34.1.1.2, 02:12:46, Serial1/1
     12.0.0.0/24 is subnetted, 1 subnets
O E1    12.1.1.0 [110/84] via 23.1.1.1, 00:00:06, Serial1/0
     14.0.0.0/24 is subnetted, 1 subnets
O E2    14.1.1.0 [110/20] via 34.1.1.2, 02:10:59, Serial1/1

总结：
1，路由器优选路由时先比较AD值，再比较metric值；
2，先解决重发布路由器上的路由回馈及选路不加问题；
3，解决其他路由器选路不佳问题。
4，抓取路由，改变指定更新源的AD值
5，抓取路由，重发布时使用route-map改变其metric值
6，抓取路由，使用offset-list增大in或out方向的metric值