OSPF选路：
O路由优于OIA：
在R1和R3上同时宣告一条相同路由，R1进area 1 R3进area0,这样，R4会收到两条路由，一条是R1发送的O，一条是R2发送的OIA。
R4会选择O路由，将1过来的路由AD变大，O路由还是优于OIA
R4路由表：
44.0.0.0/32 is subnetted, 1 subnets
O 44.44.44.44 [110/2] via 14.0.0.1, 00:00:01, FastEthernet2/0
加大R1过来的AD：
44.0.0.0/32 is subnetted, 1 subnets
O 44.44.44.44 [140/2] via 14.0.0.1, 00:00:04, FastEthernet2/0
加大Metric：
R4：ip ospf cost 6000
R4路由表：
44.0.0.0/32 is subnetted, 1 subnets
O 44.44.44.44 [140/6001] via 14.0.0.1, 00:03:31, FastEthernet2/0
干掉R1上的44.44.44.44路由，再看
44.0.0.0/32 is subnetted, 1 subnets
O IA 44.44.44.44 [110/3] via 24.0.0.2, 00:00:14, FastEthernet2/1
结论1：O路由由于O IA，与AD，Metirc无关。
O路由由于OE1 OE2：
R1上通告进AREA 1一个环回口 地址为3.3.3.3
R4上看：
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [140/6001] via 14.0.0.1, 00:01:26, FastEthernet2/0
distance和metric都更改过了，还是O路由
R3上更改外部路由类型试下：
redistribute static metric-type 1 subnets
R4上看：
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [140/6001] via 14.0.0.1, 00:00:09, FastEthernet2/0
关闭R1上的环回口：
33.0.0.0/32 is subnetted, 1 subnets
O E1 33.33.33.33 [110/22] via 24.0.0.2, 00:00:00, FastEthernet2/1
3.0.0.0/32 is subnetted, 1 subnets
O E1 3.3.3.3 [110/22] via 24.0.0.2, 00:00:00, FastEthernet2/1
结论2：O路由优于O E1，O E2
在R1上起一环回口，宣告进area 2，在R4上看O IA和 O E1的区别：
R4路由表：
33.0.0.0/32 is subnetted, 1 subnets
O E1 33.33.33.33 [110/22] via 24.0.0.2, 00:03:46, FastEthernet2/1
3.0.0.0/32 is subnetted, 1 subnets
O IA 3.3.3.3 [110/5] via 24.0.0.2, 00:00:06, FastEthernet2/1
在R2上改大Metric：
3.0.0.0/32 is subnetted, 1 subnets
O IA 3.3.3.3 [110/6004] via 24.0.0.2, 00:00:00, FastEthernet2/1
改大AD：
33.0.0.0/32 is subnetted, 1 subnets
O E1 33.33.33.33 [110/22] via 24.0.0.2, 00:00:13, FastEthernet2/1
3.0.0.0/32 is subnetted, 1 subnets
O IA 3.3.3.3 [140/5] via 24.0.0.2, 00:00:13, FastEthernet2/1
R3上变换外部类型以后，同样情况：
Down掉R1上环回口：
33.0.0.0/32 is subnetted, 1 subnets
O E2 33.33.33.33 [110/20] via 24.0.0.2, 00:00:01, FastEthernet2/1
3.0.0.0/32 is subnetted, 1 subnets
O E2 3.3.3.3 [110/20] via 24.0.0.2, 00:00:01, FastEthernet2/1
结论3：O IA路由优于 O E1，O E2。
将R1的外部路由更改为R3一模一样的IP地址。将R3上的外部路由类型改为O E1
这样R1重分布进OSPF的是type2 R3重分布进OSPF的是type1
看下R4路由表：
33.0.0.0/32 is subnetted, 1 subnets
O E1 33.33.33.33 [110/22] via 24.0.0.2, 00:00:16, FastEthernet2/1
3.0.0.0/32 is subnetted, 1 subnets
O E1 3.3.3.3 [110/22] via 24.0.0.2, 00:00:16, FastEthernet2/1
200.0.0.0/32 is subnetted, 1 subnets
排除了Metric的因素。
更改distance，后依然没有效果
distance 10 1.1.1.1 0.0.0.0
干掉R3上的重分布。
R4上看路由表：
33.0.0.0/32 is subnetted, 1 subnets
O E2 33.33.33.33 [10/20] via 14.0.0.1, 00:00:12, FastEthernet2/0
3.0.0.0/32 is subnetted, 1 subnets
O E2 3.3.3.3 [10/20] via 14.0.0.1, 00:00:12, FastEthernet2/0
结论4：E1优于E2
在R3上更改外部路由类型为E2，再看：
R4：
33.0.0.0/32 is subnetted, 1 subnets
O E2 33.33.33.33 [110/20] via 14.0.0.1, 00:00:05, FastEthernet2/0
3.0.0.0/32 is subnetted, 1 subnets
O E2 3.3.3.3 [110/20] via 14.0.0.1, 00:00:05, FastEthernet2/0
200.0.0.0/32 is subnetted, 1 subnets
选择了R1的外部路由，更改R3重分布时的seed metric ：
33.0.0.0/32 is subnetted, 1 subnets
O E2 33.33.33.33 [110/10] via 24.0.0.2, 00:00:02, FastEthernet2/1
3.0.0.0/32 is subnetted, 1 subnets
O E2 3.3.3.3 [110/10] via 24.0.0.2, 00:00:02, FastEthernet2/1
改小R1过来的AD
没有影响，
更改R1上重分布的COST=10 R1，R3一致，路由还是会从R3走，更改下R1的接口COST
R4连接R1：
ip ospf cost=100
看下R4路由表
33.0.0.0/32 is subnetted, 1 subnets
O E2 33.33.33.33 [110/10] via 24.0.0.2, 00:00:04, FastEthernet2/1
3.0.0.0/32 is subnetted, 1 subnets
O E2 3.3.3.3 [110/10] via 24.0.0.2, 00:00:04, FastEthernet2/1
为什么会有这种情况
R4#show ip route 3.3.3.3
Routing entry for 3.3.3.3/32
Known via "ospf 1", distance 110, metric 10, type extern 2, forward metric 2
Last update from 24.0.0.2 on FastEthernet2/1, 00:02:03 ago
Routing Descriptor Blocks:
* 24.0.0.2, from 3.3.3.3, 00:02:03 ago, via FastEthernet2/1
Route metric is 10, traffic share count is 1
R4#show ip route 3.3.3.3
Routing entry for 3.3.3.3/32
Known via "ospf 1", distance 90, metric 10, type extern 2, forward metric 100
Last update from 14.0.0.1 on FastEthernet2/0, 00:00:11 ago
Routing Descriptor Blocks:
* 14.0.0.1, from 1.1.1.1, 00:00:11 ago, via FastEthernet2/0
Route metric is 10, traffic share count is 1
收到多条E2路由的时候，先看 metric 再看 forward metric。
在R1上看，在R2，R3上做外部路由的重分布，将area 1 设置为 stub区域。
N1 N2的关系和E1，E2一样。
E2，N2的关系，同样，先看种子 metric 再看forward metric
