OSPF Stub Area and Totally-Stub Area on Cisco Packet Tracer

OSPF Area Types 3

In the previous posts we had talked about Standard and Bacbone Area types of OSPF beside Virtual-links. In this article, we will talk about the other area types of OSPF. Generally these area types are confused by the new network engieers. But after this post, I am sure that you will understand these OSPF area types very well. If you would like to learn Single Area OSPF Configuration with Packet Tracer, you can also check the relarted lesson.

In this post we will focus on configuration again, but firstly, let’s talk about the theorical part of this lesson.

You can DOWNLOAD the Packet Tracer example with .pkt format at the end of this lesson.

Stub Areas, Totally-Stub Areas, Not So Stubby Areas and Totally Not So Stubby Areas are the other area types of OSPF. These area types are prevent some routes to enter the Area routers. We will check all of these one by one.

For this article, the below topology will be our reference topology.

OSPF Area Types Example Topology, Stub, Totally-Stub, NSSA, Totatlly NSSA

Stub Area

Stub Area is the area that do not accept the External LSAs(Type 5). Stub Areas accept the summary LSAs Type 3 beside the Default Route from the Backbone Area. They also do not accept Type 4 LSAs.

OSPF Stub Area with Accepted LSAs

OSPF Stub Area with Accepted LSAs

To configure an area as a Stub Area, we need to configure all the routers in this area as Stub. Because, configuring a router interface as a Stub, changes the option bits in the Hello Packets. To form a new neigbourship, the other end router need to be configured as Stub.

The cofiguration is like below:

router ospf 1
area 10 stub

On our main topology, we will configure the Area 1 as stub. The stub area configuration will be like below on both Router1 and Router3:

Router1(config)# router ospf 1
Router1(config-router)# area 1 stub
Router3(config)# router ospf 1
Router3(config-router)# area 1 stub

After this configuration, the show ip route output will be like below:

Router3#show ip route
Codes: L - local, 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, E - EGP
       i - IS-IS, 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 to network is variably subnetted, 7 subnets, 2 masks
O IA [110/2] via, 00:00:38, GigabitEthernet0/1
C is directly connected, GigabitEthernet0/1
L is directly connected, GigabitEthernet0/1
O IA [110/3] via, 00:00:28, GigabitEthernet0/1
O IA [110/4] via, 00:00:18, GigabitEthernet0/1
O IA [110/2] via, 00:00:38, GigabitEthernet0/1
O IA [110/3] via, 00:00:28, GigabitEthernet0/1
O*IA [110/2] via, 00:00:38, GigabitEthernet0/1

As you can see, Type 3, Type 4 LSAs and Default Route is in the routing table. External LSAs, Type 5 is not accepted.

Totally-Stub Area

In this Area type, beside External LSAs(Type 5), LSAs Type 3 and Type 4 are also not accepted. Only a default-route is accepted by a Totally-Stub Area.

OSPF Totally-Stubby Area with Accepted LSAs

OSPF Totally-Stubby Area with Accepted LSAs

Lesson tags: ospf, routing
Back to: CCNP Enterprise 350-401 ENCOR > OSPF

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