Previously I explained the different OSPF special area types called “stub areas”. In the next series of lessons I will show you the configuration of each OSPF stub type. Let’s start with the “normal” stub type. This is the topology that we will use:
In the picture above we have 2 areas…area 0 and area 1. I’ll use this topology to demonstrate all the OSPF area types to you. Let me show you the configuration:
R1(config)#router ospf 1 R1(config-router)#network 192.168.12.0 0.0.0.255 area 0 R1(config-router)#redistribute connected subnets
R2(config)#router ospf 1 R2(config-router)#network 192.168.12.0 0.0.0.255 area 0 R2(config-router)#network 192.168.23.0 0.0.0.255 area 1
R3(config)#router ospf 1 R3(config-router)#network 192.168.23.0 0.0.0.255 area 1
I advertised all the interfaces in the correct OSPF areas with the exception of the loopback0 interface on R1. This interface is redistributed into OSPF so it becomes a LSA Type 5.
R3#show ip route ospf O IA 192.168.12.0/24 [110/2] via 192.168.23.2, 00:08:53, FastEthernet0/0 18.104.22.168/24 is subnetted, 1 subnets O E2 22.214.171.124 [110/20] via 192.168.23.2, 00:01:16, FastEthernet0/0
When we look at R3 you’ll see network 192.168.12.0 /24 as inter-area (LSA Type 3) and 126.96.36.199 /24 as external type 2 (LSA Type 5). Now let’s change area 1 in a stub area: