Categories R&S

OSPF – Implement and troubleshoot area types – Not-so-totally-stubby area

Let’s move on to the last OSPF area type , the Not-so-totally-stubby area.

 

Theory:

 

With a Not-so-totally-stubby area, type-3 Summary LSAs, type-4 ASBR Summary LSAs, and type-5 External LSAs are removed and replaced with a type-3 Summary LSA default route.

Type-7 NSSA External LSAs are allowed to be originated inside the area.

This will reduce the routing table compare to NSSA as it will suppress all the O IA  routes.

 

 

Requirements:

 

To configure Not-so-totally-stubby area, I have remove the default-information-originate option on R10.

 

Diagram:

 

OSPF - Implement and troubleshoot area types - Not-so-totally-stubby area

 

Configuration and verification:

 

Configuration is easy, we just had to add the no-summary command on R10.

 

R10(config)#router ospf 10
R10(config-router)#area 100 nssa no-summary

 

On R11, the routing table is drastically reduce and a default route is injected by R10.

R11#sh ip route
Gateway of last resort is 10.10.101.1 to network 0.0.0.0
O*IA  0.0.0.0/0 [110/11] via 10.10.101.1, 00:43:50, Ethernet0/0
      10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

 

R10 is still translating type 7 LSAs into type 5 LSAs.

R10#            sh ip ospf 10
 Routing Process "ospf 10" with ID 100.100.100.100
 Start time: 00:00:22.413, Time elapsed: 04:35:29.678
SNIP
    Area 100
        Number of interfaces in this area is 1
        It is a NSSA area
        Perform type-7/type-5 LSA translation

 

And on R9, external route redistributed into OSPF on R11 are seen as OSPF external type 2.

R9#            sh ip route 111.11.11.11
Routing entry for 111.11.11.11/32
  Known via "ospf 10", distance 110, metric 20, type extern 2, forward metric 21
  Last update from 10.10.3.10 on Ethernet0/1, 03:57:44 ago
  Routing Descriptor Blocks:
  * 10.10.3.10, from 100.100.100.100, 03:57:44 ago, via Ethernet0/1
      Route metric is 20, traffic share count is 1

 

 

We have covered all the OSPF area type.

In the next post, we will work on multiple exit point when using stub areas.

 

 

Thank you for reading.

 

 

OSPF – Implement and troubleshoot area types – Not-so-totally-stubby area

OSPF – Implement and troubleshoot area types – Not-so-totally-stubby area