How to configure OSPF Stub Area – Network Professional Member Site

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 two areas…area 0 and area 1. I’ll use this topology to demonstrate all the OSPF area types. 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, becoming an 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
     1.0.0.0/24 is subnetted, 1 subnets
O E2    1.1.1.0 [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 1.1.1.0 /24 as external type 2 (LSA Type 5). Now let’s change area 1 to a stub area:

R2(config)#router ospf 1
R2(config-router)#area 1 stub

R3(config)#router ospf 1
R3(config-router)#area 1 stub

This is how you change it into a stub area. Now let’s see what has changed:

R3#show ip route ospf 
O IA 192.168.12.0/24 [110/2] via 192.168.23.2, 00:00:42, FastEthernet0/0
O*IA 0.0.0.0/0 [110/2] via 192.168.23.2, 00:00:42, FastEthernet0/0

The stub area blocks LSA type 5, so you no longer see network 1.1.1.0 /24. It does, however, insert a default route. That’s all there is to it.

Unit 1: Introduction to OSPF

Unit 2: OSPF Neighbor Adjacency

Unit 3: OSPF Network Types

Unit 4: OSPF Stub Areas

Unit 5: Advanced OSPF Topics