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The stub area types

The stub area types can be summarized as follows:

Stub Type--------------LSAs-------------Default Injected

Stub-------------------1,2,3,4---- ---------------YES

Totally Stubby---------1,2,default of 3-----------YES

NSSA-------------------1,2,3,4,7------------------NO

Not-So-Totally-Stubby--1,2,default3,7-------------YES

1- Why do we need to inject two default routes (LSA3 and LSA7) into Not-So-Totally-Stubby, while we inject only one route (LSA3) into Totally Stubby ?

2- It is obvious under "Default injected" we have word "Yes" for both Totally Stubby and Not-So-Totally-Stubby,,,why do we have word "Yes" under Stub area ?

11 REPLIES
Purple

Re: The stub area types

Hi,

First of all, there are a couple of errors in your table:

-- Type-4 LSAs are NOT injected into 'Stub' areas

-- Type-4 LSAs are NOT injected into 'NSSA' areas

In answer to your questions:

1. By default, only a type-3 default is injected into Not-So-Totally-Stubby areas, not a type-7 default. If you have a "normal" NSSA area, you have the option of injecting a type-7 default into it.

2. A default needs to be injected into Stub areas since they need a default route to be able to get to external destinations (since type-5s are not flooded into stub areas).

Hope that helps,

Paresh.

New Member

Re: The stub area types

Hi Paresh

((First of all, there are a couple of errors in your table:

-- Type-4 LSAs are NOT injected into 'Stub' areas

-- Type-4 LSAs are NOT injected into 'NSSA' areas))

The table that I copied here form Internetwork Expert Lab (IEWB-RS Solution Guide),,,,Are you sure there are errors,,,because I need to report to them.

Purple

Re: The stub area types

Hi,

Yes, I am absolutely sure about this.

Paresh.

PS. Pls rate posts that you find useful

New Member

Re: The stub area types

Sorry for late reply but I has not received email notification.

((Yes, I am absolutely sure about this)).

Could you please send an email to Internetwork Expert Lab about this issue mentioning version IEWB-RS Version 1 Solution Guide Lab4 page 4-27 Task 5.10 Breakdown,,,then they can modify thier version to benefit other pepole.

Purple

Re: The stub area types

Alright, I'll send an email to the GroupStudy mailing list which is monitored by the two Brians and see if they can fix their doco.

Paresh.

Ps. Pls rate helpful posts

New Member

Re: The stub area types

New Member

Re: The stub area types

Purple

Re: The stub area types

Hi Saad,

You have to understand that type-4 LSAs are intrinsically linked to type-5 LSAs. If there are no type-5 LSAs, there will be no type-4 LSAs.

Therefore, when that document states that type-5 LSAs are not allowed, it is also implying that type-4 LSAs. Try it out in a lab and you will see what I mean.

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

Regards,

Paresh.

New Member

Re: The stub area types

((Therefore, when that document states that type-5 LSAs are not allowed, it is also implying that type-4 LSAs))

You meant the document from Internetwork Expert Lab....didn't you ?

Purple

Re: The stub area types

No, I meant the cisco doc you referred to.

I see you that are still not convinced about my statement that type-4 LSAs are not injected into stub areas. Here is an extract from RFC2328 (which describes the current version of the OSPF protocol):

"As specified in Section 12.4.3, Type 4 summary-LSAs (ASBR-summary-LSAs) are never originated into stub areas."

That quote is from section 12.4.3.1 (page 137)...

There is no more authoritative source on OSPF than RFC2328.. after, all OSPF implementations need to be compliant with that RFC.

I hope that clarifies this.

Pls remember to rate posts that help.

Paresh.

Purple

Re: The stub area types

Howdy,

Here's a bit more evidence. The following quote is from RFC3101 (The OSPF Not-So-Stubby Area (NSSA) Option):

"Since Type-5 AS-external-LSAs are not flooded into NSSAs, NSSA border routers should not originate Type-4 summary-LSAs into their NSSAs. Also an NSSA's border routers never originate Type-4 summary-LSAs or the NSSA's AS boundary routers, since Type-7 AS-external-LSAs are never flooded beyond the NSSA's border."

I hope that explains it ... pls do rate the post if it helps.

Regards,

Paresh.

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