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 |
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 |
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) |
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# |
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) |
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 |
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 |
10、通过以上的方法，我们可以通过改某一个链路的管理距离让它走最佳的网络到达目的地。同时为了链路的稳定和使R2到这一网段也走R1，我们也应该在R2上做相同的操作，先看一下没改之前的route：
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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# |
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) |
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 |
两条都变成R了，都通过R1到目的网段。不会走ospf网络。
