Re: Why a transit area cannot be a stub area?

Hi everyone,

One really good OSPF question is asking what the following feature
does when enabled or disabled:
http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/ospfatc.html.
The feature is directly related to the transit area concept and causes
a lot of confusion sometimes :)

-- 
Petr Lapukhov, petr_at_INE.com
CCIE #16379 (R&S/Security/SP/Voice)
Internetwork Expert, Inc.
http://www.INE.com
Toll Free: 877-224-8987
Outside US: 775-826-4344
2009/8/24 Bryan Bartik <bbartik_at_ipexpert.com>:
> Stubs were also created with the option of not allowing type 3 LSAs (this is
> from page 133 of Moy's book "OSPF: Anatomy of an Internet Routing Protocol).
> I think this would blackhole traffic heading from the backbone toward the
> disconnected area because the stub would not have the type 3 LSAs for the
> disconnected area, just like it would type 5 LSAs. Section 12.4.3.1 of RFC
> 2328 may give a little more insight regarding this "option" for summary
> LSAs.
>
> On Mon, Aug 24, 2009 at 5:34 PM, Hoogen <hoogen82_at_gmail.com> wrote:
>
>> Hi Darby,
>> I was referring a transit area which connects disconnected area's. Sorry
>> for
>> the confusion.
>>
>> The question was Why can't we have the area's that have virtual-links to be
>> a stub area. RFC says you can't " the only reason being if the disconnected
>> area had ASBR's we have a problem transmitting Type 5 LSA's
>>
>>
>> http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094aaa.shtml#virtuallinks
>>
>> Please have a look @ line 3 of the first paragraph.." The transit area
>> cannot be a stub area". I understand it why.. like Scott pointed out.. but
>> I
>> was hoping if we do not have asbr's in the disconnected area.. there should
>> be a better answer. Best practice you do not configure it.. but just was
>> digging around for a better explanation.
>>
>> -Hoogen
>>
>>
>>
>> On Mon, Aug 24, 2009 at 4:13 PM, Darby Weaver <darby.weaver_at_gmail.com
>> >wrote:
>>
>> > Hmm...
>> >
>> > I define area a transit Area as "The Transit area" aka Area 0.
>> >
>> > Now since Area 0 is connected to every other area it seems contracdictory
>> > to me and my viewpoint to ever declare it a stub area.
>> >
>> > Each area attached to Area 0 sends its information to Area 0.
>> >
>> > Virtual-links are an extension of Area 0.
>> >
>> > So with all that said... what was the question again?
>> >
>> > I have a pretty nice powerpoint that kinda illustrates the whole picture
>> > and I guess if you stare at it long enough it starts to make sense. :)
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> > On Mon, Aug 24, 2009 at 5:15 PM, Hoogen <hoogen82_at_gmail.com> wrote:
>> >
>> >> Hi All,
>> >> I have been trying to look around but any more information would be
>> >> great...
>> >>
>> >> The only thing I understand it can't be done is because RFC says so..
>> and
>> >> because just in case the disconnected area has ASBR type 5 external
>> lsa's
>> >> cannot pass through.
>> >>
>> >> Anyone has any more information other than this?
>> >>
>> >> -Hoogen
>> >>
>> >>
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>>
>>
>>
>
>
> --
> Bryan Bartik
> CCIE #23707 (R&S), CCNP
> Sr. Support Engineer - IPexpert, Inc.
> URL: http://www.IPexpert.com
>
>
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