ospf no summary and default information originate

[fabio.marino]

Hi all,

I have very simple question and I would like to have your opinion.

I can inject default route in to a nssa area in two way

- no-summary (to be used in to the NSSA ABR or NSSA ASBR)

-default-information originate (To be used in to the NSSA ABR)

Doubts (alle the below query are referred to a nssa area)

- Case no-summary: what will happen if the nssa abr does not have a default route?

-Case default-information originate: what will happen if the nssa abr does not have a default route?

- When do I have to use no-summary and when default information originate?

-What is the benefit to use the following command area xx nssa no-summary default information originate?

Thanks!!

[Rolf Fischer]

Hi,

have a look at this document:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094a88.shtml#defaultnssa

- no-summary (to be used in to the NSSA ABR or NSSA ASBR)
-default-information originate (To be used in to the NSSA ABR or NSSA ASBR)

- Case no-summary: what will happen if the nssa abr does not have a default route?

A (summary) default-route will be injected by the NSSABR; the backbone area is supposed to have detailed routing information.

-Case default-information originate: what will happen if the nssa abr does not have a default route?

A default-route will be injected by the NSSABR; the backbone area is supposed to have detailed routing information.

- When do I have to use no-summary and when default information originate?
 -What is the benefit to use the following command area xx nssa no-summary default information originate? 

The no-summary option defines a NSSA totally stub; the NSSABR doesn't translate Backbone Area's LSAs (more precisely: their corresponding routing-table entries) into NSSA summary-LSAs, instead it injects a (summary) default route. If you want the NSSABR to do the summary-translation and also inject a default-route, you can use the default-information-originate option. A NSSABR the will inject a type-7 LSA for the default-route, which is not translated to type-5. This option can also be used on a NSSA ASBR, but in this case a non-OSPF default-route is required and a type-5 translation is possible.

[EDIT] :

Perhaps this discussion is also helpful to understand some of the design aspects of different area types:

https://supportforums.cisco.com/message/3977926#3977926

HTH

Rolf

[Rolf Fischer · Accepted solution]

-What is the benefit to use the following command area xx nssa no-summary default information originate?

This is actually a very interesting question.

Combining the no-summary- and the default-information-originate options on a NSSABR would inject a type-3 and a type-7 LSA for the default route into the NSSA (totally stub). The type-3 LSA will always be prefered over the type-7, so the default-information-originate option is somewhat redundant here.

On a NSSA (totally stub) ASBR, which is not an ABR at the same time, the no-summary option is not required, but you may however configure it for the purpose of consistent configurations, although it won't have any effect.

So an ASBR which injects a default-route into a NSSA could be an example for using both options.

HTH

Rolf

[fabio.marino]

Hi Rolf,

Thanks for the answers.

I am analising them.