Day 3 - OSPF Stub Area

Selain standar area, dalam OSPF kita juga mengenal stub area.

Stub area artinya router atau area yang paling ujung yang tidak memiliki cabang lain serta tidak memili jalan lain untuk menuju jaringan dengan segment yang lain.

Semua external LSA tipe 4 dan 5 tidak dimasukkan kedalam routing table.

Sebagai gantinya, maka digunakan default route untuk menuju network yang lain.

Hal ini akan mengurangi kinerja CPU dan Memory router, mengurangi jumlah routing table.

Stub area harus dikonfigurasikan disemua router yang berada dalam satu stub area.

Lab kali ini kita akan membahas bagaimana cara konfigurasi stub area OSPF.

Lab 4 - OSPF Stub Area

Topologi yang digunakan adalah sbb :


Skenarionya adalah untuk Area 1 akan kita jadikan stub area.
 
Konfigurasi R1 :

interface Loopback0
 ip address 1.1.1.1 255.255.255.255
!
interface Loopback1
 ip address 100.100.100.1 255.255.255.255
!
interface Loopback2
 ip address 100.100.100.2 255.255.255.255
!
interface Loopback3
 ip address 100.100.100.3 255.255.255.255
!
interface Loopback4
 ip address 100.100.100.4 255.255.255.255
!
interface Loopback5
 ip address 100.100.100.5 255.255.255.255
!
interface Loopback6
 ip address 100.100.100.6 255.255.255.255
!
interface Loopback7
 ip address 100.100.100.7 255.255.255.255
!
interface Serial0/0
 ip address 12.12.12.1 255.255.255.0
!
router eigrp 1
 network 100.100.100.4 0.0.0.0
 network 100.100.100.5 0.0.0.0
 network 100.100.100.6 0.0.0.0
 network 100.100.100.7 0.0.0.0
!

router ospf 1
 router-id 1.1.1.1
 log-adjacency-changes
 redistribute eigrp 1 subnets
 network 1.1.1.1 0.0.0.0 area 0
 network 12.12.12.1 0.0.0.0 area 0
 network 100.100.100.1 0.0.0.0 area 100
 network 100.100.100.2 0.0.0.0 area 100
 network 100.100.100.3 0.0.0.0 area 100

Konfigurasi R2 :

interface Loopback0
 ip address 2.2.2.2 255.255.255.255
!
interface FastEthernet0/0
 ip address 23.23.23.2 255.255.255.0
!
interface Serial0/0
 ip address 12.12.12.2 255.255.255.0
!

router ospf 2
 router-id 2.2.2.2
 log-adjacency-changes
 network 2.2.2.2 0.0.0.0 area 1
 network 12.12.12.2 0.0.0.0 area 0
 network 23.23.23.2 0.0.0.0 area 1

Konfigurasi 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
 log-adjacency-changes
 network 3.3.3.3 0.0.0.0 area 1
 network 23.23.23.3 0.0.0.0 area 1

Sekarang kita coba rubah untuk area 1 menjadi stub area.
Perubahan dilakukan pada router yang terhubung ke area 1, yaitu di R2 dan R3.

R2(config)#router ospf 2
R2(config-router)#area 1 stub
*Mar  1 00:25:52.859: %OSPF-5-ADJCHG: Process 2, Nbr 3.3.3.3 on FastEthernet0/0 from FULL to DOWN, Neighbor Down: Adjacency forced to reset
 

R3(config-router)#area 1 stub
R3(config-router)#
*Mar  1 00:25:53.243: %OSPF-5-ADJCHG: Process 3, Nbr 2.2.2.2 on FastEthernet0/0 from FULL to DOWN, Neighbor Down: Adjacency forced to reset

Setelah kita tunggu beberapa saat, sekarang kita cek routing table di R3 :

R3(config-router)#do sh ip route
Gateway of last resort is 23.23.23.2 to network 0.0.0.0

     1.0.0.0/32 is subnetted, 1 subnets
O IA    1.1.1.1 [110/75] via 23.23.23.2, 00:00:53, FastEthernet0/0
     2.0.0.0/32 is subnetted, 1 subnets
O       2.2.2.2 [110/11] via 23.23.23.2, 00:00:53, FastEthernet0/0
     100.0.0.0/32 is subnetted, 3 subnets
O IA    100.100.100.1 [110/75] via 23.23.23.2, 00:00:53, FastEthernet0/0
O IA    100.100.100.2 [110/75] via 23.23.23.2, 00:00:53, FastEthernet0/0
O IA    100.100.100.3 [110/75] via 23.23.23.2, 00:00:53, 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, 00:00:56, FastEthernet0/0
O*IA 0.0.0.0/0 [110/11] via 23.23.23.2, 00:00:56, FastEthernet0/0

Terlihat di R3 sudah tidak menerima routing IP Loopback R1 yang masuk ke Area 100.
Dan saat ini sudah ada default route dengan tanda O*IA yang diterima dari router R2.


Kita cek juga di ip ospf database :

R3(config-router)#do sh ip ospf database
            OSPF Router with ID (3.3.3.3) (Process ID 3)
                Router Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum Link count
2.2.2.2         2.2.2.2         89          0x80000005 0x00E489 2
3.3.3.3         3.3.3.3         88          0x80000005 0x00F56C 2

                Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
23.23.23.3      3.3.3.3         88          0x80000003 0x00CC05

                Summary Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
0.0.0.0         2.2.2.2         94          0x80000001 0x0075C0
1.1.1.1         2.2.2.2         94          0x80000002 0x00C729
12.12.12.0      2.2.2.2         94          0x80000002 0x003A97
100.100.100.1   2.2.2.2         94          0x80000002 0x00CDF8
100.100.100.2   2.2.2.2         94          0x80000002 0x00C302
100.100.100.3   2.2.2.2         94          0x80000002 0x00B90B

Terlihat bahwa dalam database OSPF, LSA tipe 4 dan 5 sudah tidak ada lagi :)