一、网络拓扑

20200816102433

为了深入理解OSPF。如上图，R1、R2、R3处于MA网络中，网段为10.0.0.0/24。每台路由器除了配置接口IP地址外，需要配置L0地址为X.X.X.X/32，同时不将L0通告进任何网络。将EIGRP网络和OSPF网络做双向重分布

二、实验准备

R1#
Int e0/0
Ip address 10.0.0.1 255.255.255.0
No sh
Int e0/1
Ip address 192.168.0.1 255.255.255.0
No sh
Int lo0
Ip address 1.1.1.1 255.255.255.255

Router ospf 1
Router-id 1.1.1.1
int e0/0
ip ospf 1 a 0
int e0/1
ip ospf 1 a 1

int e0/0
ip ospf message 1 md5 epiol
ip ospf auth message 


R2#
Int e0/0
Ip address 10.0.0.2 255.255.255.0
No sh
Int e0/1
Ip address 192.168.1.2 255.255.255.0
No sh
Ip address 2.2.2.2 255.255.255.255

int e0/0
ip ospf message 1 md5 epiol
ip ospf auth message 


Router ospf 1
Router-id 2.2.2.2
Int e0/0
Ip ospf 1 a 0
Int e0/1
Ip ospf 1 a 2

R3#
Int e0/0
Ip address 10.0.0.3 255.255.255.0
No sh
Int e0/1
Ip address 192.168.2.3 255.255.255.0
No sh
Ip address 3.3.3.3 255.255.255.255


Router ospf 1
Router-id 3.3.3.3
Int e0/0
Ip ospf 1 a 0
Int e0/1
Ip ospf 1 a 3
int e0/0
ip ospf message 1 md5 epiol
ip ospf auth message 


R4#
Int e0/0
Ip address 192.168.2.4 255.255.255.0
No sh
Int e0/1
Ip address 192.168.3.4 255.255.255.0
No sh
Ip address 4.4.4.4 255.255.255.255

Router ospf 1
Router-id 4.4.4.4
Red eigrp 1 subnets
Int e0/0
Ip ospf 1 a 3


Router eigrp 1
No auto-summary
Network 192.168.4.0 0.0.0.255
Red ospf 1 metric 10000 100 255 1 1500

R5#
Int e0/0
Ip address 192.168.0.5 255.255.255.0
No sh
Ip address 5.5.5.5 255.255.255.255


Router ospf 1
Router-id 5.5.5.5
Int e0/0
Ip ospf 1 a 1

R6#
Int e0/0
Ip address 192.168.1.6 255.255.255.0
No sh
Ip address 6.6.6.6 255.255.255.255

Router ospf 1
Router-id 6.6.6.6
Int e0/0
Ip ospf 1 a 2

R7#
Int e0/0
Ip address 192.168.3.7 255.255.255.0
No sh
Int e0/1
Ip address 192.168.4.7 255.255.255.0
No sh
Ip address 7.7.7.7 255.255.255.255

Router eigrp 1
No auto-summary
Network 192.168.3.0 0.0.0.255
Network 192.168.4.0 0.0.0.255

三、对标OSPF原理分析

1.查看OSPF信息

查看接口优先级、所属OSPF区域、IP地址/子网掩码、接口cost、state

20200816102707

2.cost计算

2.1 路由cost

20200816102811

以R5 O IA路由为例：
10.0.0.0路由的cost为20，R5 e0/0、R1 e0/0，如下图

20200816102832

192.168.1.0路由的cost为30，结论就是cost值得计算是路由学习途径的入接口总和，上图中的192.168.3.0和192.168.4.0为O E2，重分布进入OSPF后是固定的cost=20

2.2 接口cost

接口cost= (100*1000K)/接口带宽=10

20200816102942

3.组播地址

20200816103002

路由器开启OSPF后，就会自动加入到224.0.0.5和224.0.0.6中

4.DR与BDR选举流程

20200816103029

由于DR和BDR的选举在MA网络（network type BROADCAST）进行，这里的area 0 、area 1、area 2、area 3 都是MA网络，所以选取area 0来解释DR和BDR选举流程。首先R1、R2、R3各自发送hello报文以建立OSPF邻居关系，建立成功后。首先根据HELLO包中的priority来选举BDR，但是一般接口优先级都是不会更改的，默认为1。随后根据OSPF报文中的OSPF header中的router-id来比较大小，router-id大的为DR，router-id次大的为BDR，router-id小的接口为DRother。

20200816103047