一、拓扑图：
二、配置说明与分析：
1、按照拓扑图配置各路由器的IP地址和协议，并在R2和R5上做重分发，保证所有的链路的连通性。看一下R2上的重分发配置：
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R2#show run
router ospf 1
log-adjacency-changes
redistribute rip metric 200 subnets (把RIP发进OSPF过来的cost 我定义为200)
network 172.16.255.0 0.0.0.3 area 0
!
router rip
redistribute ospf 1 metric 11 (把ospf 发进RIP过来的cost 我定义为 11)
network 192.168.1.0
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2、那么应该说通过
R2这个路由后：
ospf 区域到
rip区域后
cost 将会为成为我们定义的值
11
Rip区域到
ospf 区域后
cost 将会成为我们定义的值
200
3、在RIP区域看一下ospf 区域过来的路由：
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R1# sh ip route
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
R 172.16.0.0/16 [120/11] via 192.168.1.2, 00:00:07, Serial1/1(ospf那边过来的,RIP把它当R)
10.0.0.0/24 is subnetted, 1 subnets
C 10.1.1.0 is directly connected, Loopback0
C 192.168.1.0/24 is directly connected, Serial1/1
C 192.168.2.0/24 is directly connected, FastEthernet0/0
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4、在OSPF区域看一下RIP区域过来的路由：
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R3#show ip route
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
172.16.0.0/30 is subnetted, 3 subnets
C 172.16.255.0 is directly connected, Serial1/0
C 172.16.255.4 is directly connected, Serial1/1
O 172.16.255.8 [110/128] via 172.16.255.6, 00:49:26, Serial1/1
O E2 10.0.0.0/8 [110/200] via 172.16.255.1, 00:49:26, Serial1/0
O E2 192.168.1.0/24 [110/200] via 172.16.255.1, 00:49:26, Serial1/0 (通过R2过来的定义了200)
O E1 192.168.2.0/24 [110/328] via 172.16.255.6, 00:49:26, Serial1/1(通过R5过来的，那么为什么是328呢？这条路由经过R5过来的，它会以R5上的重分发的cost值计算，因为我在R5重发布的时候做了redistribute rip metric 200 metric-type 1 subnets 这样就会叠加经过ospf 区域的cost：RIPàOSPF (cost 200) + R4—>R5 (cost 64) + R3—>R4 (cost 64) = cost 328)
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5、通过上面的图示我们弄清了rip和ospf 区域的cost值之后,现在我们在R5上看一下路由表:
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R5#show ip route
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
172.16.0.0/30 is subnetted, 3 subnets
O 172.16.255.0 [110/192] via 172.16.255.9, 00:03:00, Serial1/0
O 172.16.255.4 [110/128] via 172.16.255.9, 00:03:00, Serial1/0
C 172.16.255.8 is directly connected, Serial1/0
O E2 10.0.0.0/8 [110/200] via 172.16.255.9, 00:02:59, Serial1/0 (居然绕了4个路由器)
O E2 192.168.1.0/24 [110/200] via 172.16.255.9, 00:02:59, Serial1/0 (也绕远了,不直接通过R1走)
C 192.168.2.0/24 is directly connected, FastEthernet0/0
R5#
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6、我们看到
R5到
10.0.0.0/8和
192.168.1.0/24都是绕了个大圈通过
ospf 区域来走，那它为什么不直接通过
R1这一跳来走呢。这样路径更近，只要通过
R1一个路由器转发就行啊。呵呵！这是因为
R5认为
R2重分发过进来路由的管理距离是
110。
rip是
120，走
ospf更短。所以不选择
R1走，而是走
R4。看来管理距离决定着路由器选择那个路由协议的路径过去。所以在这种情况之后。我们要去手动地在
R5上修改到达
R1的管理距离，强制让它选择最佳路由走
R1。
7、我们可以通过一个
acl加指定链路的
distance来做：
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R5(config)#access-list 1 permit 10.0.0.0 0.255.255.255(建立一个对目的网络的访问控制列表)
R5(config)#router rip
R5(config-router)#distance 85 192.168.2.0 0.0.0.255 1(定义到R1的管理距离为85匹配access-list1)
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8、我们来看一下
access-list 1：
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R5#show access-lists 1
Standard IP access list 1
10
ermit 10.0.0.0, wildcard bits 0.255.255.255 (1 match) 已经有1个匹配了
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9、看一下
R5 的路由表：
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R5#show ip route
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
172.16.0.0/30 is subnetted, 3 subnets
O 172.16.255.0 [110/192] via 172.16.255.9, 02:32:03, Serial1/0
O 172.16.255.4 [110/128] via 172.16.255.9, 02:32:03, Serial1/0
C 172.16.255.8 is directly connected, Serial1/0
R 10.0.0.0/8 [85/1] via 192.168.2.1, 00:00:11, FastEthernet0/0 (现在变成R了，并且走R1了)
O E2 192.168.1.0/24 [110/200] via 172.16.255.9, 00:09:57, Serial1/0(这条路径加一条ACL就能改到走R1了，那样将会变成R不会是O E2)
C 192.168.2.0/24 is directly connected, FastEthernet0/0
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10
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R2#sh ip route
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
172.16.0.0/30 is subnetted, 3 subnets
C 172.16.255.0 is directly connected, Serial1/1
O 172.16.255.4 [110/128] via 172.16.255.2, 02:46:52, Serial1/1
O 172.16.255.8 [110/192] via 172.16.255.2, 02:46:52, Serial1/1
O E1 10.0.0.0/8 [110/392] via 172.16.255.2, 00:15:01, Serial1/1
C 192.168.1.0/24 is directly connected, Serial1/0
O E1 192.168.2.0/24 [110/392] via 172.16.255.2, 02:46:52, Serial1/1
R2#
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11、这次我来把两条都改掉管理距离让它们走
R1：
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R2(config)#access-list 1 permit 10.0.0.0 0.0.0.255 (建立第一个到目的网络的访问控制列表)
R2(config)#access-list 1 permit 192.168.2.0 0.0.0.255(建立第二个到目的网络的访问控制列表)
R2(config)#router rip
R2(config-router)#distance 85 192.168.1.1 0.0.0.0 1 (设定到R1的管理距离)
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12、再来看一下R2的route:
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R2(config-router)#do sho ip route
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
172.16.0.0/30 is subnetted, 3 subnets
C 172.16.255.0 is directly connected, Serial1/1
O 172.16.255.4 [110/128] via 172.16.255.2, 04:12:19, Serial1/1
O 172.16.255.8 [110/192] via 172.16.255.2, 04:12:19, Serial1/1
R 10.0.0.0/8 [85/1] via 192.168.1.1, 00:00:18, Serial1/0
C 192.168.1.0/24 is directly connected, Serial1/0
R 192.168.2.0/24 [85/1] via 192.168.1.1, 00:00:18, Serial1/0
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两条都变成
R了，都通过
R1到目的网段。不会走ospf网络。
本文转自wxs-163 51CTO博客，原文链接:http://blog.51cto.com/supercisco/251983
