Re: 3 OSPF non-zero areas

Jared's actually right on target with this method of thinking... As a
cool way of studying (even though there's a plethora of variety between
all the vendors!) a candidate should be able to take any existing
scenario and start thinking about "what if....?".

Never fear to create your own modifications to things, or even your own
labs for that matter. For years, I've been telling people to work
towards this. The cool thing (as seen below) is that you'll end up
creating some REALLY ugly scenarios. But if you can think your way
through them, you're doing great on your comfort level with the technology!

Don't fear making mistakes! Every once and a while, you will
create/dream an impossible scenario. Something that simply cannot
happen. By the time you've worked at it, thought about it, labbed at it
and tried to make it work, you have at least been spending time thinking
about the protocol. No value is lost there.

Any complicated task before you can be broken down into a series of
simple tasks. That level of visualization though, requires a lot of
work! :)

*Scott Morris*, CCIE/x4/ (R&S/ISP-Dial/Security/Service Provider) #4713,

JNCIE-M #153, JNCIS-ER, CISSP, et al.

JNCI-M, JNCI-ER

smorris_at_internetworkexpert.com

Internetwork Expert, Inc.

http://www.InternetworkExpert.com

Toll Free: 877-224-8987

Outside US: 775-826-4344

Knowledge is power.

Power corrupts.

Study hard and be Eeeeviiiil......

Jared Scrivener wrote:
> Every router has a connected route between them. Forget the numbered
> areas - Would the 3 contiguous GRE tunnels create a contiguous Area 0?
> I can't see why not. From there it follows that every other router's
> numbered area interfaces could be advertised into OSPF without
> incident (as if they were loopbacks). This won't force the control
> plane path via the data plane path to build the control plane path (my
> description of tunnel recursion) as the numbered OSPF areas are going
> to be learned via OSPF with a Tunnel interface next hop (which is
> fine) and the GRE packets that carry the OSPF packets will be routed
> via the connected routes as each GRE packet is going over a single hop
> to a directly connected neighbor.
>
> A more difficult question (here's a gauntlet thrown down) is what
> would happen if there was an area router in the middle of each area
> (between R1 and R2, R2 and R3 etc)? Please don't lab this up and paste
> the configs until everyone has a chance to visualize and discuss this
> (explain your reasoning from first principles). It's a great thought
> experiment so pick an answer THEN prove it on hardware (if you can
> visualize this, you can do anything - this kind if puzzle is as hard
> as it gets).
>
> Game on. :)
>
> Cheers,
>
> Jared
>
> PS If you see three numbered areas and can't create area zero you can
> redistribute each area into the adjacent one other by putting them in
> separate processes (ASBRs and no ABRs). No need for tunnels (the least
> preferable method). Redistributing between multiple processes should
> be your second preferred method (VLs between routers and adding a
> loopback in Area 0 is method number one of course, if allowed).
>
>
> On May 5, 2009, at 10:28 PM, Anthony Sequeira
> <asequeira_at_internetworkexpert.com> wrote:
>
>> I think Anantha is really going "outside the box" here as he has NO
>> area 0 at all.
>>
>> It is really late for me, but I am thinking the only time we can go
>> without an Area 0 in OSPF is when we only have a single area.
>>
>> Warmest Regards,
>>
>> Anthony J. Sequeira, CCIE #15626
>> Senior CCIE Instructor
>> http://www.InternetworkExpert.com
>>
>> Internetwork Expert, Inc.
>> Toll Free: 877-224-8987
>> Outside US: 775-826-4344
>>
>> Test your Core Knowledge today!
>> Q: What is the BGP synchronization rule?
>> A: This rule states that a router will not use or advertise a route
>> learned by IBGP until a matching route has been learned from an IGP.
>> More Info:
>> www.cisco.com/en/US/docs/ios/12_2/ip/configuration/guide/1cfbgp.html#wp1002910
>>
>>
>> On May 6, 2009, at 1:01 AM, Roy Waterman wrote:
>>
>>> Sorry what i meant to say was:
>>>
>>> You can create a virtual link to extend area 0 to area 4, and then
>>> create a
>>> 2nd virtual link to extend area 0 (which was extended to area 4) to
>>> area 5.
>>>
>>> 2009/5/6 Roy Waterman <roy.waterman_at_gmail.com>
>>>
>>>> Hi Anantha
>>>> You can create a virtual link to extend area 0 to area 4, and then
>>>> create a
>>>> 2nd virtual link to extend area4 to area 5.
>>>>
>>>>
>>>> 2009/5/6 Anantha Subramanian Natarajan
>>>> <anantha.natarajan_at_gravitant.com>
>>>>
>>>> Hi All,
>>>>>
>>>>> Is it possible to run OSPF when there are three OSPF areas as
>>>>> shown below
>>>>> and none of them is not a area 0.
>>>>>
>>>>> R1 --ospf area3 --R2 ---ospf area4 ---R3 ----ospf area5 --R4
>>>>>
>>>>> My understanding is that, virtual-link would be only useful when
>>>>> to join a
>>>>> non-zero area to connect to area0 which is seperated by another
>>>>> non-zero area.Also the virtual links would be useful in case where
>>>>> area 0
>>>>> is
>>>>> broken in between a non-zero area.Assuming my above understanding is
>>>>> right,I
>>>>> am thinking the above scenario will not be able to use virtual
>>>>> links to
>>>>> propagate OSPF routes among R1,R2,R3,R4.
>>>>>
>>>>> In this case,if I would be able to build GRE tunnel between
>>>>> R1-R2,R2-R3,R3-R4 and run OSPF on area0 over them,In that
>>>>> case,will the
>>>>> OSPF
>>>>> routes would be able to get propagated ?
>>>>>
>>>>> Thanks for the help
>>>>>
>>>>> Regards
>>>>> Anantha Subramanian Natarajan
>>>>>
>>>>>
>>>>> Blogs and organic groups at http://www.ccie.net
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>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> Regards
>>>> Roy
>>>>
>>>
>>>
>>>
>>> --
>>> Regards
>>> Roy
>>>
>>>
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Received on Wed May 06 2009 - 06:49:09 ART