From: Salau, Yemi (yemi.salau@siemens.com)
Date: Wed May 21 2008 - 09:27:54 ART
No it's not, for the so called discontiguous networks, you can use
tunnel interfaces/vpn to bridge into the backbone area, be careful
though on the real environment.
You don't want to have 2 Area0's do you, at least not what the RFC
recommends if you don't want to confuse the hell out of your OSPF
routers ... ie. which link-database to believe. So, you ideally also
want to "bridge" the two Area0s. What of if you're merging two different
companies' OSPF networks, well ... that's where BGP comes in handy, I'm
sure there are other ways to achieve this also.
One thing I need to also note is that it's possible to have multiple
instances of a non-backbone area as long as they have ABR connecting to
the Backbone area, and you don't need a virtual link in this case.
Although, the Design/Architect guys would normally object to this, as
it's suboptimal and can cause issues. Still looking/digging through the
RFC that mitigates against the fundamental design principles for this
though.
So if you have Area2-------Area0------Area2 This needs no virtual
link/tunnel interfaces, and will work, I've done it several times in my
office; but is not best practise from design perspective
But if you have Area0------Area1-------Area2 You have to hook Area2 up
back to Area0 (hope this make some sense); Golden OSPF Area Rules: All
areas must have a link/leg in Area0, and there should only be one Area0
Many Thanks
Yemi Salau
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
ahmed badr
Sent: Wednesday, May 21, 2008 12:53 PM
To: Ina&Laurean
Cc: Miguel Trejo; Cisco certification
Subject: Re: OSPF areas
In cisco CCIE Exam certification guide, the author recommends that if
you
have discontiguous or partitioned area, you should link it by Virtual
link.
this is to have the same LSA database in the area.
I LABed it without virtual links and it worked. *is this a MUST??*
Also the more important question is that: what if the discontiguous area
is
area 0. i.e I have
area 0 ---->area 5 ----> area 0
should I connect area0s together using a virtual link?
I also LABed that and it worked ok without virtual links. *is this a
MUST
too?*
2008/5/15 Ina&Laurean <ina.laurean@gmail.com>:
> Depending on IP address space on Area 5 you may experince problems if
you
> want to summarize.
> A single summary route for Area 5 won't work if you don't link the two
> sections together.
>
> Laurean
>
>
>
> On Wed, May 14, 2008 at 9:31 PM, Miguel Trejo <mike.trejo@gmail.com>
> wrote:
>
>> The main reason behind this working with no problem is that LSA
doesn't
>> carry out area information once they are injected as inter-area
routes. So
>> when they reach the "other"area 5 that ABR doesn't care about the
original
>> area this belonged to, only about the ABR that originated the route
as the
>> routers inside the "other" area 5 only care that this ABR knows how
to
>> reach
>> the remote networks. OSPF is alink state protocol only at area level,
when
>> talking about routes to networks in other areas we rely on what the
ABR
>> says, pretty much like distance vector.
>>
>>
>> On Sat, May 10, 2008 at 3:51 PM, ahmed badr <eng.ahmedbadr@gmail.com>
>> wrote:
>>
>> > ok I got it. thnx
>> >
>> >
>> >
>> > 2008/5/10 Ibrahim kabir <kebramccie@live.com>:
>> >
>> > > yeah jason i meant OI i.e inter-area routes. The terms keep
confusing
>> me
>> > > inter(btween areas) and intra(within same) area.
>> > >
>> > > Kabir K Ibrahim
>> > > B.sc CCNA CCNP CCDP CCNP MCP
>> > > +2348036477283
>> > >
>> > >
>> > > > Date: Sat, 10 May 2008 08:23:43 -0600
>> > > > From: madsen.jason@gmail.com
>> > > > To: kebramccie@live.com
>> > > > Subject: Re: OSPF areas
>> > > > CC: eng.ahmedbadr@gmail.com; ccielab@groupstudy.com
>> > >
>> > > >
>> > > > correct, a virtual link doesn't seem appropriate here. Kebram,
I
>> think
>> > > you
>> > > > meant that the discontiguous area 5s are seeing each other as
>> > inter-area
>> > > > routes and not intra-area routes, right? each area 5 should end
up
>> > being
>> > > > it's own unique area unless a tunnel is used.
>> > > >
>> > > > Jason
>> > > >
>> > > > On Sat, May 10, 2008 at 6:15 AM, Ibrahim kabir
<kebramccie@live.com
>> >
>> > > wrote:
>> > > >
>> > > > > Ahmed,
>> > > > >
>> > > > > neva thought about this type of design at all. bt i labbed it
and
>> it
>> > > worked
>> > > > > without gre or virtual-links. The main thing to look out for
is
>> that
>> > > each
>> > > > > area
>> > > > > should be connected to the backbone area (Area 0). and
looking at
>> > your
>> > > > > diagram the condition is true. only that the discontigious
area
>> 5's
>> > see
>> > > > > each
>> > > > > others routes as intra-area routes.
>> > > > > Lab it and see for urself.
>> > > > > cheers,
>> > > > > kebram
>> > > > >
>> > > > >
>> > > > > > Date: Sat, 10 May 2008 13:30:06 +0300> From:
>> > eng.ahmedbadr@gmail.com
>> > > >
>> > > > > To:
>> > > > > ccielab@groupstudy.com> Subject: OSPF areas> > Dears,> >
>> according
>> > to
>> > > the
>> > > > > diagram below, should I link area 5 in the two sides by any>
mean
>> (eg
>> > > > > tunnel)
>> > > > > or it should work fine.> > > > Area5 Area0 Area5>
>> -------------------
>> > > > > ----------- ------------------> - - - - - -> -
--R1-----------
>> > > > > R2------------R3------------R4-- -> - - - - - ->
>> -------------------
>> > > > > ----------- -------------------> > >
>> > > > >
>> > >
>>
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