OSPF中非backbone区域被分割的解决方法 推荐

area 2被area 0和area 5分割，

预配置：
R1



R2



R3



R5



R4



按照拓扑启用OSPF
R1


R2



R3



R4



R5





这时全网已经启用了OSPF，我们只看R2和R5上路由表的状态

R2(config-router)#
R2(config-router)#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, 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
12.0.0.0/8 is variably subnetted, 10 subnets, 2 masks
O IA 12.12.5.5/32 [110/85] via 12.12.12.1, 00:05:18, Ethernet0/0
O IA 12.12.4.4/32 [110/65] via 12.12.24.4, 00:05:23, Serial0/1
O IA 12.12.3.3/32 [110/75] via 12.12.12.1, 00:05:23, Ethernet0/0
C 12.12.2.2/32 is directly connected, Loopback0
O IA 12.12.1.1/32 [110/11] via 12.12.12.1, 00:05:23, Ethernet0/0
C 12.12.12.0/24 is directly connected, Ethernet0/0
C 12.12.24.0/24 is directly connected, Serial0/1
O IA 12.12.34.0/24 [110/74] via 12.12.12.1, 00:05:24, Ethernet0/0
O IA 12.12.35.0/24 [110/84] via 12.12.12.1, 00:05:24, Ethernet0/0
O IA 12.12.50.0/24 [110/94] via 12.12.12.1, 00:00:41, Ethernet0/0
R2(config-router)#

R5(config-router)#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
12.0.0.0/8 is variably subnetted, 10 subnets, 2 masks
C 12.12.5.5/32 is directly connected, Loopback0
O 12.12.4.4/32 [110/75] via 12.12.35.3, 00:01:04, Ethernet0
O 12.12.3.3/32 [110/11] via 12.12.35.3, 00:01:04, Ethernet0
O IA 12.12.2.2/32 [110/85] via 12.12.35.3, 00:01:04, Ethernet0
O 12.12.1.1/32 [110/75] via 12.12.35.3, 00:01:04, Ethernet0
O IA 12.12.12.0/24 [110/84] via 12.12.35.3, 00:01:04, Ethernet0
O IA 12.12.24.0/24 [110/138] via 12.12.35.3, 00:01:04, Ethernet0
O 12.12.34.0/24 [110/74] via 12.12.35.3, 00:01:05, Ethernet0
C 12.12.35.0/24 is directly connected, Ethernet0
C 12.12.50.0/24 is directly connected, Ethernet1

虽然R2和R5的e0口在同一个区域，但是显示收到对方路由状态显示为O IA，这说明在R2和R5上都认为是通过外部区域学到的路由，

解决方法
通过在R1到R5，R4到R5上建立GRE tunnel









这时R2和R5路由表的状态
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, 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
12.0.0.0/8 is variably subnetted, 10 subnets, 2 masks
O IA 12.12.5.5/32 [110/85] via 12.12.12.1, 00:01:29, Ethernet0/0
O IA 12.12.4.4/32 [110/65] via 12.12.24.4, 00:01:29, Serial0/1
O IA 12.12.3.3/32 [110/75] via 12.12.12.1, 00:01:29, Ethernet0/0
C 12.12.2.2/32 is directly connected, Loopback0
O IA 12.12.1.1/32 [110/11] via 12.12.12.1, 00:01:29, Ethernet0/0
C 12.12.12.0/24 is directly connected, Ethernet0/0
C 12.12.24.0/24 is directly connected, Serial0/1
O IA 12.12.34.0/24 [110/74] via 12.12.12.1, 00:01:30, Ethernet0/0
O IA 12.12.35.0/24 [110/84] via 12.12.12.1, 00:01:30, Ethernet0/0
O 12.12.50.0/24 [110/11131] via 12.12.12.1, 00:01:30, Ethernet0/0

R5#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
12.0.0.0/8 is variably subnetted, 10 subnets, 2 masks
C 12.12.5.5/32 is directly connected, Loopback0
O IA 12.12.4.4/32 [110/75] via 12.12.35.3, 00:01:40, Ethernet0
O IA 12.12.3.3/32 [110/11] via 12.12.35.3, 00:01:40, Ethernet0
O 12.12.2.2/32 [110/11122] via 12.12.12.1, 00:01:40, Tunnel0
O IA 12.12.1.1/32 [110/75] via 12.12.35.3, 00:01:40, Ethernet0
O 12.12.12.0/24 [110/11121] via 12.12.12.1, 00:01:40, Tunnel0
O 12.12.24.0/24 [110/11175] via 12.12.24.4, 00:01:40, Tunnel1
O IA 12.12.34.0/24 [110/74] via 12.12.35.3, 00:01:41, Ethernet0
C 12.12.35.0/24 is directly connected, Ethernet0
C 12.12.50.0/24 is directly connected, Ethernet1

这时路由表显示的状态说明，R2和R5的e0接口为同一区域