OSPF NSSA Area

[vpalania]

Hi,

Consider there are two ABRs connecting a NSSA area to the backbone, do both ABRs convert the Type7 LSA into Type5 LSA for backbone.Also, clear what is the case of stub area , do both ABRs arvertise routes into backbone area ?

Thanks,

Vijay

[pkhatri]

Hi Vijay,

In such a case, only one of the ABRs will perform the translation - this will be the ABR with the highest router ID.

In case of a stub area, both ABRs will advertise routes for that area into the backbone.

Hope that helps - pls rate the post if it does.

Paresh

[Harold Ritter]

Vijay,

Only the the ABR with the highest RID will assume the type 7 to type 5 translation as specified in RFC 1587 paragraph 4.1:

"4.1 Translating Type-7 LSAs Into Type-5 LSAs

This step is performed as part of the NSSA's Dijkstra calculation after type-5 and type-7 routes have been calculated. If the calculating router is not an area border router this translation algorithm should be skipped. All reachable area border routers in the NSSA should now be examined noting the one with the highest router ID. If this router has the highest router ID, it will be the one translating type-7 LSAs into type-5 LSAs for the NSSA, otherwise the translation algorithm should not be performed."

In a non-NSA stub area, all ABRs advertise routes from the specific area to the backbone.

Hope this helps,

[pkhatri]

Hey Harold,

While you are here, I might as well ask you something that I've never been able to clear up - does Cisco support RFC3101 ? In my experience, it does not appear that IOS currently has support for it. If not, could you advise if it's in the roadmap ?

Thanks,

Paresh

[Harold Ritter]

Paresh,

According to the following document, IOS is RFC3101 compliant. Can you please tell me which specific feature you are referring to when you say that IOS doesn't appear to be compliant.

Thanks,

http://www.cisco.com/en/US/products/ps6350/prod_bulletin0900aecd802eaa4f.html

[pkhatri]

Thanks for looking that up, Harold.

RFC3101 introduces the NSSATranslatorRole parameter which can be used to influence the selection of the NSSA Translator. The last time I checked, I could not find a way to configure that within IOS....

Paresh

[Harold Ritter]

Paresh,

This doesn't seem to be available indeed. I will try to get more information on this.

Thanks,