R1
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
ip address 12.12.12.1 255.255.255.0
!
router ospf 1
router-id 1.1.1.1
log-adjacency-changes
network 1.1.1.1 0.0.0.0 area 0
network 12.12.12.1 0.0.0.0 area 1
R2
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0/0
ip address 12.12.12.2 255.255.255.0
!
!
interface FastEthernet0/0
ip address 23.23.23.2 255.255.255.0
!
router ospf 2
router-id 2.2.2.2
network 2.2.2.2 0.0.0.0 area 1
network 12.12.12.2 0.0.0.0 area 1
network 23.23.23.2 0.0.0.0 area 2
R3
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface FastEthernet0/0
ip address 23.23.23.3 255.255.255.0
!
router ospf 3
router-id 3.3.3.3
network 3.3.3.3 0.0.0.0 area 3
network 23.23.23.3 0.0.0.0 area 2
As you know, that all area must connect to area backbone (area 0). In this case we have area 3 that only connect to area 2. There are 2 ways what I know to solve the issue :
1. using virtual link that I will show now and
2. using tunneling
R1(config-if)#do sh ip rout
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
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/65] via 12.12.12.2, 00:02:55, Serial0/0
12.0.0.0/24 is subnetted, 1 subnets
C 12.12.12.0 is directly connected, Serial0/0
R2(config-if)#do sh ip rou
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
1.0.0.0/32 is subnetted, 1 subnets
O IA 1.1.1.1 [110/65] via 12.12.12.1, 00:03:14, Serial0/0
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback0
23.0.0.0/24 is subnetted, 1 subnets
C 23.23.23.0 is directly connected, FastEthernet0/0
12.0.0.0/24 is subnetted, 1 subnets
C 12.12.12.0 is directly connected, Serial0/0
R3(config-router)#do sh ip rout
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
3.0.0.0/32 is subnetted, 1 subnets
C 3.3.3.3 is directly connected, Loopback0
23.0.0.0/24 is subnetted, 1 subnets
C 23.23.23.0 is directly connected, FastEthernet0/0
R3(config-router)#do sh ip ospf int brie
Interface PID Area IP Address/Mask Cost State Nbrs F/C
Fa0/0 3 2 23.23.23.3/24 10 DR 1/1
Lo0 3 3 3.3.3.3/32 1 LOOP 0/0
So R1 do not get any route for all IP that not connect to area 0
R1(config-if)#do sh ip ospf data
OSPF Router with ID (1.1.1.1) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 301 0x80000004 0x00CD54 1
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
2.2.2.2 1.1.1.1 296 0x80000001 0x009B54
12.12.12.0 1.1.1.1 296 0x80000001 0x003C98
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 301 0x80000004 0x00CD79 2
2.2.2.2 2.2.2.2 302 0x80000003 0x002FFB 3
Summary Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
1.1.1.1 1.1.1.1 301 0x80000001 0x0047EC
R2(config)#do sh ip ospf data
OSPF Router with ID (2.2.2.2) (Process ID 2)
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 332 0x80000004 0x00CD79 2
2.2.2.2 2.2.2.2 331 0x80000003 0x002FFB 3
Summary Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
1.1.1.1 1.1.1.1 333 0x80000001 0x0047EC
Router Link States (Area 2)
Link ID ADV Router Age Seq# Checksum Link count
2.2.2.2 2.2.2.2 186 0x80000003 0x0095F2 1
3.3.3.3 3.3.3.3 188 0x80000002 0x005927 1
Net Link States (Area 2)
Link ID ADV Router Age Seq# Checksum
23.23.23.3 3.3.3.3 188 0x80000001 0x00B21F
R3(config-router)#do sh ip ospf data
OSPF Router with ID (3.3.3.3) (Process ID 3)
Router Link States (Area 2)
Link ID ADV Router Age Seq# Checksum Link count
2.2.2.2 2.2.2.2 212 0x80000003 0x0095F2 1
3.3.3.3 3.3.3.3 212 0x80000002 0x005927 1
Net Link States (Area 2)
Link ID ADV Router Age Seq# Checksum
23.23.23.3 3.3.3.3 212 0x80000001 0x00B21F
Router Link States (Area 3)
Link ID ADV Router Age Seq# Checksum Link count
3.3.3.3 3.3.3.3 307 0x80000001 0x007C91 1
Let's make a link from R2 to R1
R2(config-if)#router ospf 2
R2(config-router)#area 1 virtual-link 1.1.1.1
You will get message in R1 because no any virtual-link in R1.
*Mar 1 00:34:20.567: %OSPF-4-ERRRCV: Received invalid packet: mismatch area ID, from backbone area must be virtual-link but not found from 12.12.12.2, Serial0/0
R1(config-router)#router ospf 1
R1(config-router)#area 1 virtual-link 2.2.2.2
Now area 1 already connect to area backbone. You can check in R1
R3(config-router)#do sh ip rou
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
1.0.0.0/32 is subnetted, 1 subnets
O IA 1.1.1.1 [110/75] via 23.23.23.2, 00:01:04, FastEthernet0/0
2.0.0.0/32 is subnetted, 1 subnets
O IA 2.2.2.2 [110/11] via 23.23.23.2, 00:01:27, FastEthernet0/0
3.0.0.0/32 is subnetted, 1 subnets
C 3.3.3.3 is directly connected, Loopback0
23.0.0.0/24 is subnetted, 1 subnets
C 23.23.23.0 is directly connected, FastEthernet0/0
12.0.0.0/24 is subnetted, 1 subnets
O IA 12.12.12.0 [110/74] via 23.23.23.2, 00:01:27, FastEthernet0/0
Let's connect area 2 and 3 to area backbone
R3(config-router)#area 2 virtual-link 2.2.2.2
R2(config-router)#area 2 virtual-link 3.3.3.3
Now area 2 & 3 already connect to area backbone. Please check again!
R1(config-router)#do sh ip rout
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
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/65] via 12.12.12.2, 00:10:22, Serial0/0
3.0.0.0/32 is subnetted, 1 subnets
O IA 3.3.3.3 [110/75] via 12.12.12.2, 00:00:38, Serial0/0
23.0.0.0/24 is subnetted, 1 subnets
O IA 23.23.23.0 [110/74] via 12.12.12.2, 00:03:20, Serial0/0
12.0.0.0/24 is subnetted, 1 subnets
C 12.12.12.0 is directly connected, Serial0/0
R2(config-router)#do sh ip rout
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
1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/65] via 12.12.12.1, 00:03:42, Serial0/0
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O IA 3.3.3.3 [110/11] via 23.23.23.3, 00:01:10, FastEthernet0/0
23.0.0.0/24 is subnetted, 1 subnets
C 23.23.23.0 is directly connected, FastEthernet0/0
12.0.0.0/24 is subnetted, 1 subnets
C 12.12.12.0 is directly connected, Serial0/0
R3(config-router)#do sh ip rou
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
1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/75] via 23.23.23.2, 00:01:29, FastEthernet0/0
2.0.0.0/32 is subnetted, 1 subnets
O IA 2.2.2.2 [110/11] via 23.23.23.2, 00:01:29, FastEthernet0/0
3.0.0.0/32 is subnetted, 1 subnets
C 3.3.3.3 is directly connected, Loopback0
23.0.0.0/24 is subnetted, 1 subnets
C 23.23.23.0 is directly connected, FastEthernet0/0
12.0.0.0/24 is subnetted, 1 subnets
O IA 12.12.12.0 [110/74] via 23.23.23.2, 00:01:29, FastEthernet0/0
In OSPF all database should be the same within one area. Please note that make it virtual-link using router-id. If no router-id, it will choose from loopback or if no loopback will choose from interface. For checking router-id in OSPF can use command "show ip ospf" or "show ip ospf database".
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