OSPf区域路由选路实验（原创）

看到一道题如下拓扑，问R4到达R2为选择哪条路，当时拿不准，所以设计了这个拓扑加以证明，最后证明了自己的结论。如果R4通过两条链接到达R2的COST均相等的话，就会进行负载均衡。

在这个拓扑里，根本就没有O路由与OIA路由的区别，因为OSPF是链路状态路由协议，R4从两条不同链路到达R2均是OIA的路由。

 

拓扑如下：

 

 

配置如下：

R1的配置

interface Loopback0
 ip address 1.1.1.1 255.255.255.255

interface Serial1/1
 ip address 10.10.12.1 255.255.255.252
 serial restart-delay 0
!
interface Serial1/2
 ip address 10.10.14.1 255.255.255.252
 encapsulation frame-relay
 serial restart-delay 0
 frame-relay map ip 10.10.14.2 104 broadcast //这里的广播参数并不代表OSPF在HELLO包可以广播出去。
 no frame-relay inverse-arp
!

router ospf 100
 router-id 1.1.1.1
 log-adjacency-changes
 network 1.1.1.1 0.0.0.0 area 1
 network 10.10.12.0 0.0.0.3 area 1
 network 10.10.14.0 0.0.0.3 area 1
 neighbor 10.10.14.2    //这里一定要指定邻居，使用单播建立邻居，因为在帧中继网络中，OSPF的网络类型为非广播多路访问，必须指定邻居。

//指定邻居，一定要使用直连接口，使用环回口建立不成功。

R2的配置

interface Loopback0
 ip address 2.2.2.2 255.255.255.255

interface Serial1/0
 ip address 10.10.12.2 255.255.255.252
 serial restart-delay 0
 clock rate 64000
!
interface Serial1/1
 ip address 10.10.23.1 255.255.255.252
 serial restart-delay 0
 clock rate 64000

router ospf 100
 router-id 2.2.2.2
 log-adjacency-changes
 network 2.2.2.2 0.0.0.0 area 0
 network 10.10.12.0 0.0.0.3 area 1
 network 10.10.23.0 0.0.0.3 area 0
!

R3的配置

interface Loopback0
 ip address 3.3.3.3 255.255.255.255

interface Serial1/0
 ip address 10.10.23.2 255.255.255.252
 serial restart-delay 0
!
interface Serial1/1
 ip address 10.10.34.1 255.255.255.252
 serial restart-delay 0
 clock rate 64000

router ospf 100
 router-id 3.3.3.3
 log-adjacency-changes
 network 3.3.3.3 0.0.0.0 area 0
 network 10.10.23.0 0.0.0.3 area 0
 network 10.10.34.0 0.0.0.3 area 1

R4的配置

interface Loopback0
 ip address 4.4.4.4 255.255.255.255

interface Serial1/0
 ip address 10.10.34.2 255.255.255.252
 serial restart-delay 0

 

interface Serial1/2
 ip address 10.10.14.2 255.255.255.252
 encapsulation frame-relay
 ip ospf priority 100
 serial restart-delay 0
 frame-relay map ip 10.10.14.1 401 broadcast
 no frame-relay inverse-arp

router ospf 100
 router-id 4.4.4.4
 log-adjacency-changes
 network 4.4.4.4 0.0.0.0 area 1
 network 10.10.14.0 0.0.0.3 area 1
 network 10.10.34.0 0.0.0.3 area 1
 neighbor 10.10.14.1 //指定邻居，一定要使用直连接口，使用环回口建立不成功。

R1的路由表：

R1(config)#do 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

     1.0.0.0/32 is subnetted, 1 subnets
C       1.1.1.1 is directly connected, Loopback0
     2.0.0.0/32 is subnetted, 1 subnets
O IA    2.2.2.2 [110/65] via 10.10.12.2, 01:57:18, Serial1/1
     3.0.0.0/32 is subnetted, 1 subnets
O IA    3.3.3.3 [110/129] via 10.10.14.2, 01:57:18, Serial1/2
                [110/129] via 10.10.12.2, 01:57:18, Serial1/1
     4.0.0.0/32 is subnetted, 1 subnets
O       4.4.4.4 [110/65] via 10.10.14.2, 01:57:18, Serial1/2
     10.0.0.0/30 is subnetted, 4 subnets
C       10.10.12.0 is directly connected, Serial1/1
C       10.10.14.0 is directly connected, Serial1/2
O IA    10.10.23.0 [110/128] via 10.10.12.2, 01:57:18, Serial1/1
O       10.10.34.0 [110/128] via 10.10.14.2, 01:57:29, Serial1/2

R1#traceroute 3.3.3.3

Type escape sequence to abort.
Tracing the route to 3.3.3.3

  1 10.10.14.2 40 msec
    10.10.12.2 8 msec
    10.10.14.2 24 msec
  2 10.10.23.2 80 msec
    10.10.34.1 76 msec *

我们看到，由于R1到R3有两条链路，而且COST相等，进行了负载。

 

R4#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

     1.0.0.0/32 is subnetted, 1 subnets
O       1.1.1.1 [110/65] via 10.10.14.1, 02:03:32, Serial1/2
     2.0.0.0/32 is subnetted, 1 subnets
O IA    2.2.2.2 [110/129] via 10.10.34.1, 02:03:32, Serial1/0
                [110/129] via 10.10.14.1, 02:03:32, Serial1/2
     3.0.0.0/32 is subnetted, 1 subnets
O IA    3.3.3.3 [110/65] via 10.10.34.1, 02:03:32, Serial1/0
     4.0.0.0/32 is subnetted, 1 subnets
C       4.4.4.4 is directly connected, Loopback0
     10.0.0.0/30 is subnetted, 4 subnets
O       10.10.12.0 [110/128] via 10.10.14.1, 02:03:32, Serial1/2
C       10.10.14.0 is directly connected, Serial1/2
O IA    10.10.23.0 [110/128] via 10.10.34.1, 02:03:32, Serial1/0
C       10.10.34.0 is directly connected, Serial1/0
R4#
R4#tr
R4#traceroute 2.2.2.2

Type escape sequence to abort.
Tracing the route to 2.2.2.2

  1 10.10.34.1 68 msec
    10.10.14.1 4 msec
    10.10.34.1 16 msec
  2 10.10.12.2 52 msec
    10.10.23.1 28 msec *
R4#

R4上面也是这样，出现了负载。