Re: 3 OSPF non-zero areas

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
>
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> Q: What is the BGP synchronization rule?
> A: This rule states that a router will not use or advertise a route
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>
> 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
>>>>
>>>>
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>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>> --
>>> Regards
>>> Roy
>>>
>>
>>
>>
>> --
>> Regards
>> Roy
>>
>>
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Received on Wed May 06 2009 - 00:05:21 ART