Hi Mahesh,
The purpose of defining a virtual link is to "connect" an area to Area 0. If I understand correctly from your post, you have Area 12 which is not directly connected to Area 0. In this case, you have to make a virtual link between one of the ABRs of Area 0 to one of the ABRs of Area 12.
In the above case, you have to make a virtual link between R2 and R3 and it will look like that:
R2:
router ospf 1
router-id 2.2.2.2
log-adjacency-changes
area 20 virtual-link 3.3.3.3
network 10.10.12.2 0.0.0.0 area 0
network 10.10.23.2 0.0.0.0 area 20
R2#sh ip os int b
Interface PID Area IP Address/Mask Cost State Nbrs F/C
VL0 1 0 10.10.23.2/24 10 P2P 1/1
Fa0/0 1 0 10.10.12.2/24 10 DR 1/1
Fa0/1 1 20 10.10.23.2/24 10 BDR 1/1
R3:
router ospf 1
router-id 3.3.3.3
log-adjacency-changes
area 20 virtual-link 2.2.2.2
network 10.10.23.3 0.0.0.0 area 20
network 10.10.34.3 0.0.0.0 area 12
R3#sh ip os int b
Interface PID Area IP Address/Mask Cost State Nbrs F/C
VL0 1 0 10.10.23.3/24 10 P2P 1/1
Fa0/0 1 12 10.10.34.3/24 10 BDR 1/1
Fa0/1 1 20 10.10.23.3/24 10 DR 1/1
Now, R3 virtually has an interface in Area 0, even though it is not connected to Area 0.
Hope this helps.
Hey Mahesh18,
Based on the information you've provided above...below I've drawn your OSPF design (dashed line is the virtual link).
If my drawing is accurate then the following steps will connect area 12 to area 0 and get you on your way. Note: This assumes all interfaces are up and reachable.
1. On R4 - under the OSPF process configure the following
- area 20 virtual-link [R2 router-id]
2. On R2 - uncer the OSPF process configure the following
- area 20 virtual-link [R4 router-id]
That's all there is... Hope this helps!
