OSPF選路：
O路由優於OIA：
在R1和R3上同時宣告一條相同路由，R1進area 1 R3進area0,這樣，R4會收到兩條路由，一條是R1發送的O，一條是R2發送的OIA。
R4會選擇O路由，將1過來的路由AD變大，O路由還是優於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過來的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
幹掉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
結論1：O路由由於O IA，與AD，Metirc無關。
O路由由於OE1 OE2：
R1上通告進AREA 1一個環回口 地址爲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都更改過了，還是O路由
R3上更改外部路由類型試下：
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
關閉R1上的環回口：
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
結論2：O路由優於O E1，O E2
在R1上起一環回口，宣告進area 2，在R4上看O IA和 O E1的區別：
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上變換外部類型以後，同樣情況：
Down掉R1上環回口：
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
結論3：O IA路由優於 O E1，O E2。
將R1的外部路由更改爲R3一模一樣的IP地址。將R3上的外部路由類型改爲O E1
這樣R1重分佈進OSPF的是type2 R3重分佈進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，後依然沒有效果
distance 10 1.1.1.1 0.0.0.0
幹掉R3上的重分佈。
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
結論4：E1優於E2
在R3上更改外部路由類型爲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
選擇了R1的外部路由，更改R3重分佈時的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過來的AD
沒有影響，
更改R1上重分佈的COST=10 R1，R3一致，路由還是會從R3走，更改下R1的接口COST
R4連接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
爲什麼會有這種情況
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
收到多條E2路由的時候，先看 metric 再看 forward metric。
在R1上看，在R2，R3上做外部路由的重分佈，將area 1 設置爲 stub區域。
N1 N2的關係和E1，E2一樣。
E2，N2的關係，同樣，先看種子 metric 再看forward metric