Question about Type 5 route availability within NSSA

[craj]

Hi,

I have a topology as below:

                                      bgp1 [multiple specific route]
                                       |
                                       |
rip1 [specific route]----asbr-area1----abr----area(0)----abr----asbr-area2-nssa [injecting default route]----bgp3 [internet]
                                        |
                                        |
                                      rip2 [multiple specific route]

rip 1/2 & bgp1 was redistributed into area0, which will appear as type 5, and will not pass nssa area 2

-----------------------------------------------

Question is:
1. I need to allow rip specific routes within area 2 - which is not working as type 5 route from area 2 will never reach a nssa area
2. Need to stop all other updates towards area 2 - so created a nssa
3. Cannot inject a default route within area 2 from area0 abr, as a default route already coming from internet

Any suggestion?

regards,

[Giuseppe Larosa]

Hello @craj ,

in a case like yours you need to revert area 2 NSSA to a standard area so that specific RIP injected routes in form of LSA type 5 can reach all routers in area 2.

Unfortunately you cannot achieve all the three points that you have listed at the same time:

>>1. I need to allow rip specific routes within area 2 - which is not working as type 5 route from area 2 will never reach a nssa area
>>2. Need to stop all other updates towards area 2 - so created a nssa
>>3. Cannot inject a default route within area 2 from area0 abr, as a default route already coming from internet

Of course if area 2 will become a standard OSPF area it will receive all the external routes that are injected into OSPF domain by ASBR in area 1.

OSPF does not provide a granular control / filtering over external routes it is an ON/OFF or you get all of them using a standard area or you get none of them using a stub area or NSSA area.

An NSSA area can perform selective "upload" of external routes by creating LSA type 7 and converting them (if the P bit is set) at the ABR router with the highest OSPF RID.

Hope to help

Giuseppe

[Joseph W. Doherty]

Have you considered making area 2 a different OSPF domain? If you do, then you should be able to have full control over what routes are redistributed, both ways.