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OSPF Stub Area, Totally-Stub Area,

NSSA and Totally NSSA





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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.

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 HERE.

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 10.2.0.1 to network 0.0.0.0

     10.0.0.0/8 is variably subnetted, 7 subnets, 2 masks
O IA    10.1.0.0/24 [110/2] via 10.2.0.1, 00:00:38, GigabitEthernet0/1
C       10.2.0.0/24 is directly connected, GigabitEthernet0/1
L       10.2.0.2/32 is directly connected, GigabitEthernet0/1
O IA    10.3.0.0/24 [110/3] via 10.2.0.1, 00:00:28, GigabitEthernet0/1
O IA    10.4.0.0/24 [110/4] via 10.2.0.1, 00:00:18, GigabitEthernet0/1
O IA    10.6.0.0/24 [110/2] via 10.2.0.1, 00:00:38, GigabitEthernet0/1
O IA    10.7.0.0/24 [110/3] via 10.2.0.1, 00:00:28, GigabitEthernet0/1
O*IA 0.0.0.0/0 [110/2] via 10.2.0.1, 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


To configure an area as Totally-Stub, you need to configure only the ABR of that area. Configuring an area as Totally-Stub do not affect the Hello packets. So all the routers do not need to be configured for totatly-stub in the area.

The configuration will be like below:

router ospf 1
area 10 stub no-summary

On our main topology, we will configure the Area 3 as totally stubby area. The totally stubby area configuration will be like below on both Router7 and Router1:

Router7(config)# router ospf 1
Router7(config-router)# area 3 stub no-summary

Router1(config)# router ospf 1
Router1(config-router)# area 3 stub no-summary

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

Router7#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 10.6.0.1 to network 0.0.0.0

     10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C       10.6.0.0/24 is directly connected, GigabitEthernet0/2
L       10.6.0.2/32 is directly connected, GigabitEthernet0/2
O*IA 0.0.0.0/0 [110/2] via 10.6.0.1, 00:14:26, GigabitEthernet0/2

As you can see above output, there is only one default route on routing table. There is no Type3, Type 4 and Type 5 LSAs.

Not So Stubby Area (NSSA)



Not So Stubby Area name is the most funny name in network world, I think : ) Funny and useful. With NSSA, the External LSAs (Type 5) that is not accepted by Stub Areas, accepted as Type 7.

Normally, NSSA are do not accept Type 5 LSAs. But it convert Type 5 to Type 7 and then accept. After NSSA, at the ABR, this convert process is done again and Type 7 LSAs is converted to Type 5 LSAs.

OSPF NSSA  with Accepted LSAs

OSPF NSSA with Accepted LSAs


The routes that is related to Type 7 LSAs, will be like N1 and N2 routes in the routing table.The difference between these two route type is explained before.

In NSSA, Summary LSA Type 3 is accepted like Stub Area. Beside, if a default-information originate command is used in ABR, default-route is also accepted.

To configure NSSA, all the routers in the area need to be configured as NSSA. This configuration is like below:

router ospf 1
area 10 nssa

For default-route, the below command is used:

area 10 nssa default-information-originate

On our main topology, we will configure the Area 2 as not so stubby area (NSSA). The not so stubby area (NSSA) configuration will be like below on Router2, Router4 and Router5:

Router2(config)# router ospf 1
Router2(config-router)# area 2 nssa

Router4(config)# router ospf 1
Router4(config-router)# area 2 nssa

Router6(config)# router ospf 1
Router6(config-router)# area 2 nssa

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

Router4#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 not set

     10.0.0.0/8 is variably subnetted, 9 subnets, 2 masks
O IA    10.1.0.0/24 [110/2] via 10.3.0.1, 00:19:27, GigabitEthernet0/1
O IA    10.2.0.0/24 [110/3] via 10.3.0.1, 00:19:27, GigabitEthernet0/1
C       10.3.0.0/24 is directly connected, GigabitEthernet0/1
L       10.3.0.2/32 is directly connected, GigabitEthernet0/1
C       10.4.0.0/24 is directly connected, GigabitEthernet0/0
L       10.4.0.1/32 is directly connected, GigabitEthernet0/0
O N2    10.5.0.0/24 [110/100] via 10.4.0.2, 00:19:42, GigabitEthernet0/0
O IA    10.6.0.0/24 [110/3] via 10.3.0.1, 00:19:27, GigabitEthernet0/1
O IA    10.7.0.0/24 [110/2] via 10.3.0.1, 00:19:27, GigabitEthernet0/1

Here, you will see an output like stub area, but there is one difference. This difference is Type 7 LSA and External Route, N2.

Totally Not So Stubby Area (NSSA)



Totally Not So Stubby Area is like Not So Stubby Area except one diffference. In Totally NSSA, Summary LSAs(Type 3 and Type 4) are also not accepted. It get these with only one default route. And this is configured ar ABR by default-information-originate command.

OSPF Totally NSSA  with Accepted LSAs

OSPF Totally NSSA with Accepted LSAs


To configure an area as totally NSSA, only the ABR is configured. This is enough, because it do not change anythin in Hello Packet.

This configuretion is done like below:

router ospf 1
area 10 nssa no-summary

On our main topology, we will configure the Area 4 as totally not so stubby area (Totally NSSA). Totally NSSA configuration will be like below on Router2 and Router4:

Router2(config)# router ospf 1
Router2(config-router)# area 2 nssa no-summary

Router4(config)# router ospf 1
Router4(config-router)# area 2 nssa no-summary

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

Router8#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 10.7.0.1 to network 0.0.0.0

     10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C       10.7.0.0/24 is directly connected, GigabitEthernet0/2
L       10.7.0.2/32 is directly connected, GigabitEthernet0/2
O*IA 0.0.0.0/0 [110/2] via 10.7.0.1, 00:22:54, GigabitEthernet0/2

Here, in the output you will see only a default route.

In this article, we have talked about the OSPF Area Types and their configurations.You can find the packet tracer example below.

You can DOWNLOAD the Packet Tracer example with .pkt format HERE.



************************************************************
WouLd YoU LiKe To Learn How to Use PAcket TraceR and PracTice CCNA LAbs
on PaCKet TrAcEr??? Here is My Courses on UDemY!!
CISCO PACKET TRACER HOW TO GUIDE
CISCO PACKET TRACER CCNA LABS ADVENTURE 1
CISCO PACKET TRACER CCNA LABS ADVENTURE 2
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You can download “Packet Tracer” in Tools section.

OSPF Area Types on Packet Tracer – Part 1 (Standard Area, Backbone Area, Virtual-Link)
OSPF Area Types on Packet Tracer – Part 2 (OSPF External Routes)
OSPF Area Types on Packet Tracer – Part 3 (Stub Area, Totally-Stub Area, NSSA, Totally NSSA)

You can check some of the other Packet Tracer Examples below:

Common Cisco Router Configuration Example on Packet Tracer
Router DHCP Configuration Example on Packet Tracer
VTP Configuration Example on Packet Tracer
VLAN Configuration Example on Packet Tracer
STP Configuration Example on Packet Tracer
BGP Configuration Example on Packet Tracer
Port Security Configuration Example on Packet Tracer
RIP Configuration Example on Packet Tracer
CDP Configuration Example on Packet Tracer
OSPF Area Types Example on Packet Tracer (Standard and Backbone Areas)
OSPF External Routes Example on Packet Tracer
OSPF Area Types Example on Packet Tracer (Stub, NSSA, Totally Stubby, Totally NSSA Areas)

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About the Author
Gokhan Kosem is a telecommunation and network engineer. His ambition to IP networks and end-to-end system installation made him to prepare this web-site. By sharing his experiences about various networking protocols beside different system installation experiences and Cisco, Juniper, Alcatel-Lucent devices configurations, he is aimed to be helpful for his collegues in all over the world. He is currently lives in Istanbul, Turkey.

One comment for “OSPF Area Types on Packet Tracer – Part 3 (Stub Area, Totally-Stub Area, NSSA, Totally NSSA)”

1
jamal

this website is amazing . simple and full of knowledge . thank you

January 2nd, 2017 at 17:52

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