Edit the intra area comment clearly a poor guess.
Ok just read Petr's PDF too he's basically referring to what we'd not consider #3 to actually be #3 i.e non-zero area to non-zero area by means of a VL, essentially the requirement of a type 3 LSA is still valid to cross areas.
-- BR Tony Sent from my iPhone on 3 On 27 Sep 2013, at 08:40, Tony Singh <mothafungla_at_gmail.com> wrote: > > For what it's worth I totally agree as we're transiting through area 0 and the newly established ABR (after a VL has been established to a genuine area 0 ABR) to exit into an say fir example O E2 destination..... > > I think by #3 they mean O intra this is my only thinking, but for OIA we'd have to traverse an area 0 ABR for a non zero area to get to another non zero area i.e it would have to receive a type 3 LSA in the first place from the ABR. > > -- > BR > > Tony > > Sent from my iPhone on 3 > > On 27 Sep 2013, at 07:43, Joe Astorino <joeastorino1982_at_gmail.com> wrote: > >> With the default capability transit all you are doing is taking a transit area to get to area 0 instead of taking a VL through the same transit area. In both cases you still end up in area 0 then pass through area 0 to get to the other nonbackbone area. >> >> >> Sent from my iPhone >> >>> On Sep 27, 2013, at 2:41 AM, Joe Astorino <joeastorino1982_at_gmail.com> wrote: >>> >>> In my mind no because the stated rule 3 says for "a path crossing areas" "take the shortest path to the destination without crossing area 0" >>> >>> With a virtual link scenario, you ride the VL which is in area 0 to an ABR. For a router in a nonzero area to reach a route in another nonzero area, even with the virtual link you still pass through area 0 at some stage. >>> >>> Say you have area3---area0---area1---area2 >>> You would build a VL from area 2 to area 0 transmitting through area 1. If a packet wants to get to area 3 from area 2 , it rides an area 0 link to the backbone (the VL) first (rule 1) Then it would take the shortest path through area 0 (rule 2) >>> >>> Once I to area 0 though I don't see how it would get to area 3 "without crossing area 0" >>> >>> >>> >>> Sent from my iPhone >>> >>>> On Sep 27, 2013, at 1:59 AM, Tony Singh <mothafungla_at_gmail.com> wrote: >>>> >>>> >>>> The non-zero router becomes an ABR when it connects via a VL into an area 0 router. >>>> >>>> So technically is this really point 3? >>>> >>>> -- >>>> BR >>>> >>>> Tony >>>> >>>> Sent from my iPhone on 3 >>>> >>>>> On 27 Sep 2013, at 06:26, Joe Astorino <joeastorino1982_at_gmail.com> wrote: >>>>> >>>>> Yes of course, but as we know the VL is just a link in area 0 so that is not really what I'm getting at. There is also the case with the default capability transit where you can ride a transit area INTO the backbone instead of the VL but one way or another for inter area traffic you end up in the backbone >>>>> >>>>> Sent from my iPhone >>>>> >>>>>> On Sep 27, 2013, at 1:03 AM, daniel.dib_at_reaper.nu wrote: >>>>>> >>>>>> Hi Joe! >>>>>> >>>>>> This could happen if you have a virtual link between ABRs >>>>>> meaning that you have something Like Area 0 - Area 1 - Area 2. Check >>>>>> this INE blog post for the full info: >>>>>> >>>>>> >>>>>> http://blog.ine.com/2009/09/14/understanding-ospf-transit-capability/ >>>>>> [4] >>>>>> >>>>>> Regards Daniel >>>>>> >>>>>> CCIE #37149 >>>>>> >>>>>> 2013-09-27 06:17 skrev Joe >>>>>> Astorino: >>>>>> >>>>>>> So this has actually been bothering me now for YEARS. In >>>>>> the CCIE RS Exam >>>>>>> Certification Guide, there is a paragraph that goes >>>>>> something like this: >>>>>>> >>>>>>> *OSPF has specific rules for selecting a path >>>>>> that crosses areas. * >>>>>>> >>>>>>> *1) Take the shortest path to area 0. >>>>>>> 2) >>>>>> Take the shortest path across area 0 without traversing a nonzero >>>>>> area. >>>>>>> 3) Take the shortest path to the destination without traversing >>>>>> area 0.* >>>>>>> >>>>>>> This has always been somewhat vague and even disturbing to >>>>>> me. It's >>>>>>> seemingly vague and no other explanation is given about this >>>>>> process. Rule >>>>>>> 1, take the shortest path to area 0 makes sense. Once >>>>>> you get to the >>>>>>> backbone area, rule #2 even makes sense. But rule #3 >>>>>> has never and does not >>>>>>> make sense to me >>>>>>> >>>>>>> So far as I recall, an >>>>>> OSPF ABR will never accept type 3 summary LSA >>>>>>> information from a >>>>>> non-backbone area. In other words, If an ABR receives >>>>>>> inter-area >>>>>> routing information for a non-backbone area from a non-backbone >>>>>>> area >>>>>> it is ignored. This makes sure that inter area routing information is >>>>>> only learned from the backbone area, and is also a loop prevention >>>>>> mechanism. Further, in my mind it guarantees that all inter-area >>>>>> traffic >>>>>>> must transit the backbone. >>>>>>> >>>>>>> With that being said, can >>>>>> anybody think of ANY case EVER where rule #3 is >>>>>>> even valid? How would >>>>>> it ever be possible for inter-area traffic to get to >>>>>>> a destination >>>>>> without traversing area 0? >>>>>>> >>>>>>> -- >>>>>>> Regards, >>>>>>> >>>>>>> Joe Astorino >>>>>>> CCIE >>>>>> #24347 >>>>>>> http://astorinonetworks.com [1] >>>>>>> >>>>>>> "He not busy being born is >>>>>> busy dying" - Dylan >>>>>>> >>>>>>> Blogs and organic groups at http://www.ccie.net >>>>>> [2] >>>>>> _______________________________________________________________________ >>>>>> Subscription information may be found at: >>>>>> http://www.groupstudy.com/list/CCIELab.html [3] >>>>>> >>>>>> >>>>>> >>>>>> Links: >>>>>> ------ >>>>>> [1] >>>>>> http://astorinonetworks.com >>>>>> [2] http://www.ccie.net >>>>>> [3] >>>>>> http://www.groupstudy.com/list/CCIELab.html >>>>>> [4] >>>>>> http://blog.ine.com/2009/09/14/understanding-ospf-transit-capability/ >>>>>> >>>>>> >>>>>> Blogs and organic groups at http://www.ccie.net >>>>>> >>>>>> _______________________________________________________________________ >>>>>> Subscription information may be found at: >>>>>> http://www.groupstudy.com/list/CCIELab.html >>>>> >>>>> >>>>> Blogs and organic groups at http://www.ccie.net >>>>> >>>>> _______________________________________________________________________ >>>>> Subscription information may be found at: >>>>> http://www.groupstudy.com/list/CCIELab.html Blogs and organic groups at http://www.ccie.netReceived on Fri Sep 27 2013 - 09:48:12 ART
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