From: Howard C. Berkowitz (hcb@gettcomm.com)
Date: Wed Jun 11 2003 - 23:59:21 GMT-3
At 8:42 AM +0800 6/12/03, huang gang wrote:
>hi,
> ospf don't require that all areas except area 0 should be continuous.
>huangg
Only in a very, very limited sense, that there's nothing violated by
having more than one area with the same ID. Another limited sense is
that a nonzero area can be discontiguous with area 0.0.0.0 if it uses
a virtual link.
But WHY would anyone deliberately want to have multiple area x's
(other than as a failure mode as a result of a partition)? There
have been a lot of questions about doing this, and I am utterly
mystified why anyone would WANT to do this deliberately. If nothing
else, it's a nightmare for documentation. If you moved a router from
one area 0.0.0.2 to another 0.0.0.2, do you really want the same
network statements?
Even if one is exploring the effect of nonzero area partitioning, set
it up as an single area with two ABRs, and perhaps one critical
internal link. By taking that link up and down, you'll get better
understanding of what happens when an area is partitioned.
The idea of having multiple areas with the same number comes up often
enough on the list that I wonder if some practice lab somewhere is
using it as a horrible example. I'd never permit it in any
operational network for which I had responsibility.
I've heard of many strange configurations rumored to be on the CCIE
lab, but this would be beyond my worst imagination if Cisco actually
asked you to do it.
>
>> Hi all,
>>
>> In the following scenario-
>>
>>
>> Area0---------Area2
>> \ |
>> \ |
>> \ |
>> \ |
>> Area2
>>
>> If the link between Area2 fails, it becomes discontiguos, this makes the
>> intra area routes to be shown as inter area routes in both the area 2
>> routers, I tested this in the lab and found no visible reachability issues.
>> Does this disconinuity create any hidden problems?
>>
>> The other question is, that if we need to repair this, can i use a virtual
>> link between Aree2 to Area 0 and then to Area 2
>> or should I use a tunnel interface on each router putting them into area 2??
>> I actually tried it using tunnel but was not able to make it work , as I was
>> still seeing some of the Area 2 routes as O IA routes.
>>
>> Thanks as always for your inputs.
>>
>> Smiles,
>>
>> Mohit.
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