Sesuai topology diatas ospf area 0 terpisah, kemudian ditengah tengahnya terdapat area 333. Disini jika saya konfigurasikan OSPF standard maka dari R1 belum dapat berkomunikasi dengan R4.

 

R1#sh ip route
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 [110/11] via 12.12.12.2, 00:24:49, FastEthernet0/0
23.0.0.0/24 is subnetted, 1 subnets
O IA 23.23.23.0 [110/74] via 12.12.12.2, 00:24:10, FastEthernet0/0
12.0.0.0/24 is subnetted, 1 subnets
C 12.12.12.0 is directly connected, FastEthernet0/0
R1#

R1#ping 1.1.1.4
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.4, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
R1#

Sebelumnya dalam pembahasan sebelumnya (lain postingan) entah dimana lupa. Jika kita punya masalah sebuah area (selain area 0) tidak terhubung langsung dengan area 0, padahal syarat OSPF sendiri haruslah terhubung langsung dengan area 0. Untuk menghubungkanya kita perlu menggunakan virtual-link atau GRE Tunnel. Nah di OSPF Discontiguous Area ini kita juga akan memanfaatkan keduanya (bisa dipilih salah satu) untuk menghubungkan 2 area yang terpisah ini (area 0).

1. Virtual-link

Pertama kita akan mencoba menggunakan virtual-link. Kalo pake virtual-link kita cuman perlu bikin virtual-link diantara R2 dan R3. Seperti begini…

R3

router ospf 1
area 333 virtual-link 3.3.3.3

R4

router ospf 1
area 333 virtual-link 2.2.2.2

Coba kita cek hasilnya

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

34.0.0.0/24 is subnetted, 1 subnets
O 34.34.34.0 [110/84] via 12.12.12.2, 00:01:03, FastEthernet0/0
1.0.0.0/32 is subnetted, 2 subnets
C 1.1.1.1 is directly connected, Loopback0
O 1.1.1.4 [110/85] via 12.12.12.2, 00:01:03, FastEthernet0/0
2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/11] via 12.12.12.2, 00:37:17, FastEthernet0/0
23.0.0.0/24 is subnetted, 1 subnets
O IA 23.23.23.0 [110/74] via 12.12.12.2, 00:36:38, FastEthernet0/0
12.0.0.0/24 is subnetted, 1 subnets
C 12.12.12.0 is directly connected, FastEthernet0/0
R1#

Nah akhir R4 sudah terlihat di tabel routing R1. Kemudian tes ping

R1#ping 1.1.1.4

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 44/103/144 ms
R1#

Noted: command area 333 virtual-link 2.2.2.2 <- pada 2.2.2.2 itu adalah router-id

2. GRE Tunnel

Kemudian kita coba pake GRE Tunnel. Pertama kita perlu bikin interface tunnelnya dulu

R2

int Tunnel1
ip addr 172.16.1.1 255.255.255.0
tunnel source 23.23.23.2
tunnel destination 23.23.23.3

R3

int Tunnel1
ip addr 172.16.1.2 255.255.255.0
tunnel source 23.23.23.3
tunnel destination 23.23.23.2

Setelah kita bikin interface tunnel lantas apakah udah langsung bisa jalan OSPFnya ? jawabanya belum. Kita perlu menambahkanya juga ke OSPF.

R2(config-if)#router ospf 1
R2(config-router)#network 172.16.1.1 0.0.0.0 area 0
*Mar 1 01:12:20.775: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on Tunnel1 from LOADING to FULL, Loading Done
R2(config-router)#

R3(config-if)#router ospf 1
R3(config-router)#network 172.16.1.2 0.0.0.0 area 0
*Mar 1 01:12:20.163: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Tunnel1 from LOADING to FULL, Loading Done
R3(config-router)#

Nah muncul notifikasi kalau OSPF tunnelnya sudah UP. Kemudian kita cek di R1, sudah ada atau belum di tabel routingnya untuk menuju R4.

<br />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
34.0.0.0/24 is subnetted, 1 subnets
O 34.34.34.0 [110/11131] via 12.12.12.2, 00:06:21, FastEthernet0/0
1.0.0.0/32 is subnetted, 2 subnets
C 1.1.1.1 is directly connected, Loopback0
O 1.1.1.4 [110/11132] via 12.12.12.2, 00:06:21, FastEthernet0/0
2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/11] via 12.12.12.2, 00:56:36, FastEthernet0/0
23.0.0.0/24 is subnetted, 1 subnets
O IA 23.23.23.0 [110/74] via 12.12.12.2, 00:55:57, FastEthernet0/0
172.16.0.0/24 is subnetted, 1 subnets
O 172.16.1.0 [110/11121] via 12.12.12.2, 00:06:39, FastEthernet0/0
12.0.0.0/24 is subnetted, 1 subnets
C 12.12.12.0 is directly connected, FastEthernet0/0
R1#

Kemudian kita cek ping

R1#ping 1.1.1.4
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 28/286/1020 ms
R1#