上面一個實驗，兩個區域，不同區域之間有相同的router-id 暫時沒有出現問題，現在這個實驗不同區域間有相同的router-id就出問題了。拓撲如下：
其中R3是ASBR，RIP與OSPF之間互相進行了重分佈，正常情況上，如果router-id沒有相同的話，R1應該可以學到R4的路由。但情況是R1的路由如下：
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
10.0.0.0/30 is subnetted, 2 subnets
C 10.10.12.0 is directly connected, Serial1/1
O IA 10.10.23.0 [110/128] via 10.10.12.2, 00:57:28, Serial1/1
C 192.168.1.0/24 is directly connected, Loopback0
R1#
再看R2路由，R2的路由多看幾次就會發現不同。
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
10.0.0.0/30 is subnetted, 3 subnets
C 10.10.12.0 is directly connected, Serial1/0
C 10.10.23.0 is directly connected, Serial1/1
O E2 10.10.34.0 [110/20] via 10.10.23.2, 00:00:05, Serial1/1
192.168.1.0/32 is subnetted, 1 subnets
O 192.168.1.1 [110/65] via 10.10.12.1, 00:09:50, Serial1/0
O E2 192.168.2.0/24 [110/20] via 10.10.23.2, 00:00:05, Serial1/1
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
10.0.0.0/30 is subnetted, 2 subnets
C 10.10.12.0 is directly connected, Serial1/0
C 10.10.23.0 is directly connected, Serial1/1
192.168.1.0/32 is subnetted, 1 subnets
O 192.168.1.1 [110/65] via 10.10.12.1, 00:09:51, Serial1/0
兩個E2路由時有時無，但R1始終沒有E2的路由。
再看一個R2的database
R2#sh ip ospf database
OSPF Router with ID (2.2.2.2) (Process ID 100)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 827 0x80000012 0x006068 3
2.2.2.2 2.2.2.2 820 0x8000000F 0x008CB5 2
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
10.10.23.0 2.2.2.2 815 0x80000001 0x00C408
Summary ASB Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
1.1.1.1 2.2.2.2 512 0x80000001 0x00935C
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 518 0x80000003 0x008DAD 2
2.2.2.2 2.2.2.2 800 0x80000002 0x00102A 2
Summary Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
10.10.12.0 2.2.2.2 821 0x80000001 0x003E99
192.168.1.1 2.2.2.2 821 0x80000001 0x001375
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
10.10.34.0 1.1.1.1 3600 0x80000066 0x00B166 0
192.168.2.0 1.1.1.1 3600 0x80000066 0x006E71 0
_____________________________________________________
好，現在修改R3的router-id 爲3.3.3.3看效果：
R3(config)#router ospf 100
R3(config-router)#router
R3(config-router)#router-id 3.3.3.3
Reload or use "clear ip ospf process" command, for this to take effect
R3(config-router)#
R3(config-router)#
R3(config-router)#
R3(config-router)#do clear ip ospf pr
% Ambiguous command: "do clear ip ospf pr"
R3(config-router)#do clear ip ospf pr
Reset ALL OSPF processes? [no]: y
再來看R1的路由，正常了。
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
10.0.0.0/30 is subnetted, 3 subnets
C 10.10.12.0 is directly connected, Serial1/1
O IA 10.10.23.0 [110/128] via 10.10.12.2, 01:01:03, Serial1/1
O E2 10.10.34.0 [110/20] via 10.10.12.2, 00:00:00, Serial1/1
C 192.168.1.0/24 is directly connected, Loopback0
O E2 192.168.2.0/24 [110/20] via 10.10.12.2, 00:00:00, Serial1/1
至於爲什麼出現這個現象，我的理解是，因爲外部路由重發布到OSPF中，在ABR傳播中， ABR不能修改其router-id ，所以當ASBR的route-id 與區域中的某一臺路由器router-id相同時就會出問題。